JP5810742B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a printer, a copying machine, or the like that heat-fixes an unfixed image on a recording sheet by using a heating element including a magnetic shunt alloy layer that generates heat by electromagnetic induction and has a Curie temperature higher than a fixing temperature. The present invention relates to an image forming apparatus, and more particularly, to a technique for preventing occurrence of uneven gloss due to a temperature difference between a paper passing area and a non-paper passing area that occurs when a recording sheet having a predetermined width is continuously passed.

In image forming apparatuses such as printers and copiers, an electromagnetic induction heating type image forming apparatus is used which is superior to a heater heating type image forming apparatus in terms of shortening the warm-up time and saving power. It has become to.
On the other hand, in an electromagnetic induction heating type image forming apparatus, since the heat capacity of a fixing member used for heat-fixing an unfixed image on a recording sheet is small, the temperature of the sheet passing area is likely to decrease due to the passing of the recording sheet. In order to maintain the temperature of the sheet passing area at the fixing temperature, the entire fixing member is heated at any time during the heat fixing operation. For this reason, when the sheet is continuously passed, the temperature difference between the sheet passing area and the non-sheet passing area of the fixing member becomes large, and as a result, the recording sheet of a small size (for example, A4 size) continues. When the heat fixing operation is performed on a large size (for example, A3 size) recording sheet after the heat fixing operation is performed, gloss unevenness caused by the temperature difference in the image after the heat fixing of the large size recording sheet is performed. May occur.

  As a technique for reducing the temperature difference generated between the paper passing area and the non-paper passing area of the fixing member, for example, Patent Document 1 includes heat generation including a magnetic shunt alloy that is set to have a Curie temperature higher than the fixing temperature. An image forming apparatus that heats a fixing member using a body and electromagnetically heats the heating element between heat fixing jobs after the end of the previous heat fixing job and the start of the next heat fixing job is disclosed. Has been.

  In the image forming apparatus of Patent Document 1, since a magnetic shunt alloy is used as a heating element, when the temperature of the heating element becomes equal to or higher than the Curie temperature, the magnetism is lost, and the temperature of the non-sheet passing region does not rise above the Curie temperature. To be suppressed. Further, the heating rate of the heating element is gradually decreased as the temperature increases toward the Curie temperature (see the description of paragraph 44 and FIG. 7), and electromagnetic induction heating of the heating element is performed between heat fixing jobs. By performing the above, the temperature difference generated between the sheet passing area and the non-sheet passing area of the fixing member is reduced.

  Specifically, when the heating element is heated by electromagnetic induction, the temperature increase rate increases in the sheet passing area where the temperature is lower than that in the non-sheet passing area. . As a result, the temperature difference generated between the sheet passing area and the non-sheet passing area of the fixing member in the previously executed heat fixing job can be effectively reduced. Even when heat fixing is performed on a recording sheet having a larger width than that of a heat fixing job, the fixing temperature in the width direction of the recording sheet is made uniform so that gloss unevenness does not occur in the image after heat fixing. Can do.

JP 2008-70757 A

However, in the technique disclosed in Patent Document 1 described above, an electromagnetic induction heating operation is performed to reduce a temperature difference generated between the sheet passing area and the non-sheet passing area of the fixing member between heat fixing jobs. In the meantime, the execution of the next heat fixing job is delayed, and the productivity of the heat fixing job is reduced accordingly.
The present invention has been made in view of the above-described problems, and is intended to reduce the temperature difference generated between the sheet passing area and the non-sheet passing area of the fixing member, and is caused by the temperature difference. An object of the present invention is to provide an image forming apparatus capable of improving the productivity of executing a heat fixing job while effectively preventing the occurrence of uneven gloss.

  In order to achieve the above object, an image forming apparatus according to an aspect of the present invention includes a magnetic shunt alloy layer that generates heat by electromagnetic induction and has a Curie temperature higher than a fixing temperature. Using a heating element whose heating rate is reduced, heat fixing of an unfixed image on a recording sheet is performed, and during execution of a print job, the temperature of the area corresponding to the sheet passing area in the heating element and its non-sheet passing area are set. When the temperature difference from the temperature of the corresponding area exceeds the limit value where gloss unevenness is allowed due to the latter temperature increase, the temperature difference becomes within the limit value after the thermal fixing of the print job is completed. An image forming apparatus that suppresses execution of heat fixing of the next print job until the temperature difference exceeds the limit value due to a temperature rise in the area corresponding to the non-sheet passing area during execution of the print job. Determine whether or not And an area corresponding to the sheet passing area by raising the temperature of the heating element from the fixing temperature within a period until the print job being executed is completed after the limit value is exceeded. Temperature control means for raising the temperature of the print job at a faster temperature rise rate than the area corresponding to the non-sheet passing area, and within the period until the thermal fixing of the print job is completed by the temperature rise by the temperature control means. And a release unit that cancels the suppression of execution of thermal fixing of the next print job when the temperature difference returns within the limit value.

Here, the determination unit may determine that the temperature difference has exceeded the limit value when the temperature of the region corresponding to the non-sheet-passing region reaches the Curie temperature.
A size specifying unit that specifies a size of a recording sheet of a print job, and the temperature control unit sets the heating element to a fixing temperature when the size of the recording sheet of the current print job and the next print job is the same. The temperature raising operation for further raising the temperature can be suppressed, and the canceling unit can cancel the suppression of execution of thermal fixing of the next print job.

  By providing the above configuration, the temperature difference with the area corresponding to the non-sheet passing area in the heating element during the execution of the print job causes a temperature difference with the area corresponding to the non-sheet passing area to be a limit value at which gloss unevenness is allowed. In the period until the current print job is completed, the heating element is heated from the fixing temperature and the temperature of the area corresponding to the sheet passing area is changed to the non-sheet passing area. If the temperature difference between the two returns to within the limit within the period until the thermal fixing of the print job is completed due to the temperature increase, the temperature Since the suppression of execution of thermal fixing of print jobs is canceled, the occurrence of uneven gloss due to the temperature difference between the two is effectively prevented, and the productivity of execution of thermal fixing jobs is increased by the amount canceled. Can do.

  Here, if the temperature difference does not return within the limit value within a period until the thermal fixing of the print job is completed, the temperature control unit may perform the process after the thermal fixing of the print job is completed. The heating element is further heated until the temperature difference returns within the limit value, and the release means further increases the temperature of the heating element, so that the temperature difference returns within the limit value. In addition, the suppression of execution of thermal fixing of the next print job may be canceled.

  As a result, the temperature difference between the temperature of the heating element in the area corresponding to the paper passing area and the temperature of the area corresponding to the non-sheet passing area is returned to the limit value within the period until the thermal fixing of the print job is completed. Even if there is not, the temperature of the area corresponding to the paper passing area of the heating element is raised at a faster heating rate than the area corresponding to the non-paper passing area during the execution of the print job. Since the heating element is further heated until the difference falls within the limit value, the time until the temperature difference between the two reaches the limit value can be shortened by the amount raised during execution of the print job. Accordingly, the execution of the next heat fixing job can be started earlier, and the productivity of executing the heat fixing job can be improved.

Here, each time the thermal fixing is performed on the recording sheet within the period until the thermal fixing of the print job is completed until the temperature difference falls within the limit value, the temperature control unit performs each thermal fixing. The temperature of the heating element may be raised in stages so that the temperature rise amount during the period does not exceed the limit temperature at which gloss unevenness does not occur during the thermal fixing process for one sheet .
As a result, heat generation is performed so that the amount of temperature increase during the period in which the thermal fixing of each recording sheet is performed within the period until the thermal fixing of the print job is completed does not exceed a limit value in which gloss unevenness is allowed. Since the body temperature is raised stepwise, it is possible to effectively prevent the occurrence of uneven glossiness on the recording sheet after heat fixing by the temperature raising operation.

Here, when the temperature difference returns to within the limit value , the temperature control unit performs the recording sheet recording within a period from the start of the thermal fixing of the next print job until the end of the thermal fixing. Each time heat fixing is performed, the amount of temperature decrease during each heat fixing is gradually increased so that the temperature does not exceed a limit temperature at which gloss unevenness does not occur during the heat fixing process for one sheet. The body temperature may be lowered until reaching the fixing temperature.
As a result, after the start of the thermal fixing of the next print job, the amount of temperature decrease during the period in which the thermal fixing of each recording sheet is performed does not exceed the limit value where the uneven glossiness is allowed. Since the temperature is gradually lowered until the temperature reaches the fixing temperature, the heat fixing operation is continued at a temperature higher than necessary, so that power consumption is not increased unnecessarily.

The thickness includes specific means, said temperature control means for specifying the thickness of the recording sheet of the print job, the thickness of the recording sheet of the print job in execution, if thinner than the thickness of the recording sheet in the next print job , in the period of Made Netsu fixing print job in execution ends, the Mai heat Teichaku is performed on Kiroku Shito, Yutaka Noboru Ryo period Kaku Netsu Teichaku is being performed, the one Netsu Teichaku Shori The temperature of the heating element is raised stepwise so as not to exceed a limit temperature at which gloss unevenness does not occur during the operation, and the release means finishes the thermal fixing of the print job by the temperature rise by the temperature control means. If the temperature of the heating element reaches a predetermined temperature suitable for thermal fixing of the recording sheet of the next print job within the period up to the fixing temperature related to the print job being executed, Thermal fixing of print jobs It may be and Turkey to release the suppression of the line.

  As a result, the thickness of the recording sheet of the current print job is thinner than the thickness of the recording sheet of the next print job, and in order to prevent fixing failure, the fixing related to the print job that is performing the thermal fixing of the next print job is performed. When it is necessary to carry out at a predetermined temperature higher than the temperature, the temperature rise amount during the period in which the thermal fixing of each recording sheet is performed within the period until the thermal fixing of the print job being executed is finished is glossy. The temperature of the heating element is raised stepwise so that the unevenness does not exceed the allowable limit value, and the temperature of the heating element is within the predetermined period within the period until the thermal fixing of the print job being executed is completed. When the temperature is reached, the suppression of the execution of thermal fixing for the next print job is canceled, so the thermal fixing of the next print job is executed when the fixing temperature is changed due to the change in the recording sheet thickness. To prevent delays Door can be.

  Here, when the temperature of the heating element does not reach the predetermined temperature within a period until the thermal fixing of the print job is completed, the temperature control means sets the temperature of the heating element to the predetermined temperature. The heating element is further heated until the temperature reaches a predetermined temperature, and the releasing means performs the thermal fixing of the next print job when the temperature of the heating element that has been further increased reaches the predetermined temperature. It is also possible to cancel the suppression.

  As a result, even if the temperature of the heating element does not reach the predetermined temperature within the period until the thermal fixing of the print job being executed is completed, the temperature of the heating element is stepwise within the period. After the temperature is raised, the heating element is further heated until the temperature of the heating element reaches the predetermined temperature. Therefore, the thickness of the recording sheet is changed by the amount raised during execution of the print job. It is possible to reduce the delay in execution of thermal fixing of the next print job due to the change in the fixing temperature.

1 is a diagram illustrating a configuration of a printer. 2 is a partial cross-sectional perspective view showing a configuration of a fixing device 5. FIG. FIG. 3 is a cross-sectional view of a main part of the fixing device 5. 3 is a diagram illustrating a relationship between a configuration of a control unit 60 and main components that are controlled by the control unit 60. FIG. It is a figure which shows the specific example of a frequency control table. FIG. 6 shows a graph formed by plotting the correspondence between control frequency and expected supply power, and control frequency and threshold supply power in the frequency control table of FIG. 2 is a circuit diagram showing an outline of an IH power supply 190. FIG. 4 is a flowchart illustrating an operation of a print job interruption control process performed by a control unit 60. 7 is a flowchart illustrating an operation of an inter-job printing process interruption temperature difference adjustment process performed by a control unit 60. FIG. 10 is a diagram schematically illustrating how the temperature of the surface temperature (t) of the fixing belt 155 is adjusted by executing the inter-job printing process interruption temperature difference adjustment process of FIG. 9. 7 is a flowchart illustrating an operation of an inter-job printing process non-interrupted temperature difference adjustment process performed by a control unit 60. FIG. 12 is a diagram schematically showing how the temperature of the surface temperature (t) of the fixing belt 155 is adjusted by executing the inter-job printing process non-interrupting temperature difference adjustment process of FIG. 11. 10 is a flowchart illustrating a modified example of the operation of the print job interruption control process. 7 is a flowchart showing an operation of inter-job printing process interruption cardboard temperature difference adjustment process 1 performed by a control unit 60. 7 is a flowchart showing an operation of an inter-job printing process uninterrupted cardboard large temperature difference adjustment process 1 performed by a control unit 60. 6 is a flowchart showing an operation of a temperature difference adjustment process 2 for a large-sized cardboard interrupted inter-job printing process performed by a control unit 60. 10 is a flowchart showing an operation of a temperature difference adjustment process 2 for non-interrupted cardboard large print processing performed by a control unit 60 between jobs. 7 is a flowchart illustrating an operation of a temperature difference adjustment process for cardboard small paper interrupted by the control unit 60. 10 is a flowchart showing an operation of a temperature difference adjustment process for non-interrupted cardboard small paper printing performed by the control unit 60.

(Embodiment)
Hereinafter, an embodiment of an image forming apparatus according to an embodiment of the present invention will be described with reference to an example in which the image forming apparatus is applied to a tandem color digital printer (hereinafter simply referred to as “printer”).
[1] Configuration of Printer First, the configuration of the printer 1 according to the present embodiment will be described. FIG. 1 is a diagram illustrating a configuration of a printer 1 according to the present embodiment. As shown in FIG. 1, the printer 1 includes an image process unit 3, a paper feed unit 4, a fixing device 5, a control unit 60, and the like.

  When the printer 1 is connected to a network (for example, LAN) and receives a print instruction from an external terminal device (not shown) or an operation panel having a display unit (not shown), yellow, magenta, cyan, and black are received based on the instruction. A toner image of each color is formed, and these are multiplex-transferred onto a recording sheet to form a full-color image, thereby executing a printing process on the recording sheet. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are expressed as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.

The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K, an exposure unit 10, an intermediate transfer belt 11, a secondary transfer roller 45, and the like. Since the image forming units 3Y, 3M, 3C, and 3K have the same configuration, the configuration of the image forming unit 3Y will be mainly described below.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. Then, a Y-color toner image is formed on the photosensitive drum 31Y. The developing device 33Y faces the photosensitive drum 31Y and conveys charged toner to the photosensitive drum 31Y. The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is driven to rotate in the direction of arrow C. A cleaner 21 for removing toner remaining on the intermediate transfer belt is disposed in the vicinity of the driven roller 13.

  The exposure unit 10 includes a light emitting element such as a laser diode, emits laser light L for forming images of Y to K colors in response to a drive signal from the control unit 60, and each of the image forming units 3Y, 3M, 3C, and 3K. The photosensitive drum is exposed and scanned. By this exposure scanning, an electrostatic latent image is formed on the photosensitive drum 31Y charged by the charger 32Y. Similarly, electrostatic latent images are formed on the photosensitive drums of the image forming units 3M, 3C, and 3K.

The electrostatic latent image formed on each photoconductor drum is developed by each developing unit of the image forming units 3Y, 3M, 3C, and 3K, and a toner image of a corresponding color is formed on each photoconductor drum. The formed toner images are assigned with primary transfer rollers of image forming units 3Y, 3M, 3C, and 3K (in FIG. 1, only the primary transfer roller corresponding to the image forming unit 3Y is denoted by reference numeral 34Y, and other primary transfer rollers). , The primary transfer is sequentially performed on the intermediate transfer belt 11 at different timings so as to be superimposed at the same position on the intermediate transfer belt 11, and then by the secondary transfer roller 45. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet by the action of electrostatic force.

The recording sheet on which the toner image has been secondarily transferred is further conveyed to the fixing device 5, and the toner image (unfixed image) on the recording sheet is heated and pressed in the fixing device 5 and thermally fixed on the recording sheet. Thereafter, the paper is discharged onto a paper discharge tray 72 by a discharge roller 71.
The paper feed unit 4 includes a paper feed cassette 41 that stores recording sheets (denoted by reference numeral S in FIG. 1), a feed roller 42 that feeds the recording sheets in the paper feed cassette 41 one by one onto the transport path 43, and a feed roller 42. A timing roller 44 for conveying the recording sheet at a timing for sending the recording sheet to the secondary transfer position 46 is provided.

The number of paper feed cassettes is not limited to one and may be plural. As the recording sheet, paper sheets (plain paper, thick paper) having different sizes and thicknesses, and film sheets such as an OHP sheet can be used. When there are a plurality of paper feed cassettes, recording sheets having different sizes, thicknesses or materials may be stored in the paper feed cassettes.
The timing roller 44 prints the recording sheet in synchronization with the timing at which the toner image primarily transferred onto the intermediate transfer belt 11 is conveyed to the secondary transfer position 46 so as to be superimposed at the same position on the intermediate transfer belt 11. It is conveyed to the next transfer position 46. Then, at the secondary transfer position 46, the toner images on the intermediate transfer belt 11 are secondarily transferred onto the recording sheet by the secondary transfer roller 45.

Each of the rollers such as the feeding roller 42 and the timing roller 44 is rotationally driven through a power transmission mechanism (not shown) such as a gear and a belt using a transport motor (not shown) as a power source. As the transport motor, for example, a stepping motor capable of controlling the rotational speed with high accuracy is used.
[2] Configuration of Fixing Device FIG. 2 is a partial cross-sectional perspective view showing the configuration of the fixing device 5, and FIG. 3 is a cross-sectional view of the main part thereof. 3A shows a cross-sectional view of the fixing device 5, and FIG. 3B is a partial cross-sectional view showing the detailed structure of the fixing belt 155 (the portion indicated by the dotted rectangle C in FIG. 3A). Indicates. Hereinafter, the configuration of the fixing device 5 will be described in detail with reference to FIGS. 2, 3A, and 3B.

  As shown in FIG. 2, the fixing device 5 is an electromagnetic induction heating type fixing device, and includes a fixing roller 150, a fixing belt 155, a guide plate 156, a pressure roller 160, a magnetic flux generator 170, a central server. And Mr. 180. The area indicated by reference numeral P in the figure indicates a non-passing area on the fixing belt 155 where a recording sheet indicated by reference numeral S (here, plain paper, A4 size) is not passed.

The fixing roller 150 is configured by covering an elongated cylindrical cored bar 152 with an elastic body layer 153, and as shown in FIG. 3A, the fixing roller 155 has an inner circumference path (circular running path) inside. Is arranged. As the size of the fixing roller 150, for example, one having an outer diameter of 36 mm can be used.
The cored bar 152 is a member that supports the fixing roller 150, and is formed of a cylindrical body having an outer diameter of about 20 mm, for example. As a material constituting the cored bar 152, for example, aluminum, iron, stainless steel, or the like can be used.

  The elastic layer 153 prevents the heat generated by the fixing belt 155 from escaping to the cored bar 152 and, as shown in FIG. 3A, the pressure roller 160 and the fixing nip (155n) via the fixing belt 155. It is a layer for forming. The thickness of the elastic body layer 153 can be 8 mm, for example. As a material constituting the elastic body layer 153, a material having high heat resistance and high heat insulation is desirable. For example, a foaming elastic body such as silicone rubber or fluororubber can be used.

The fixing belt 155 is an endless belt, and as shown in FIG. 3B, a magnetic shunt alloy layer 155a, an elastic body layer 155b, and a release layer 155c are laminated in this order. . A heat generating layer made of nickel, copper, or the like may be provided between the magnetic shunt alloy layer 155a and the elastic body layer 155b.
The magnetic shunt alloy layer 155a is a ferromagnetic material until reaching the Curie temperature, and has a property of becoming a paramagnetic material when the Curie temperature is reached. This is a layer that suppresses the temperature rise of the fixing belt 155 due to electromagnetic induction when the temperature is raised and reaches the Curie temperature.

  The thickness of the magnetic shunt alloy layer 155a can be about 30 μm, for example. As a material constituting the magnetic shunt alloy layer 155a, for example, an alloy of nickel and iron can be used. The Curie temperature of the magnetic shunt alloy layer 155a is set to a desired temperature by adjusting the mixing ratio of nickel and iron. Here, it is assumed that the Curie temperature of the magnetic shunt alloy layer 155a is set to a temperature (eg, about 220 ° C.) that is about 40 ° C. higher than the fixing temperature (eg, about 180 ° C.).

  When the Curie temperature is set to a temperature close to the fixing temperature (for example, a temperature at which the temperature difference from the fixing temperature does not exceed a limit value (for example, 10 ° C.) at which gloss unevenness is allowed (for example, about 190 ° C.)) Since the temperature rise rate of the fixing belt 155 is greatly reduced by the time the temperature of 155 reaches the fixing temperature, the warm-up time until the heat fixing operation is started is disadvantageously increased. It is desirable to set the temperature difference to a temperature exceeding a limit value at which gloss unevenness is allowed.

If the Curie temperature is set too high than the fixing temperature, the temperature of the fixing belt 155 is raised in a print job interruption control process described later, and the high temperature side (non-sheet passing area side) of the fixing belt 155 is set. When controlling the temperature so that the temperature difference between the two and the low temperature side (paper passing area side) is eliminated, if the temperature does not become much higher than the fixing temperature, Since it does not increase, there is a disadvantage that power consumption for temperature control increases. Therefore, it is desirable to set the Curie temperature so as not to be higher by 50 ° C. than the fixing temperature.
Further, an alloy of nickel, iron, and chromium may be used as a material constituting the magnetic shunt alloy layer 155a.

  The elastic body layer 155b is a layer for transferring heat uniformly and flexibly to the toner image on the recording sheet. By providing the elastic body layer 155b, the toner image can be prevented from being crushed or the toner image can be melted non-uniformly, and image noise can be prevented from being generated. The thickness of the elastic body layer 155b can be about 200 μm, for example. As a material constituting the elastic body layer 155b, a rubber material or a resin material having heat resistance and elasticity can be used. For example, silicone rubber or fluorine rubber can be used.

  The release layer 155c is an outermost layer of the fixing belt 155, and is a layer for improving the release property between the fixing belt 155 and the recording sheet. The thickness of the release layer 155c is 5 to 100 μm, desirably 10 to 50 μm. As the material constituting the release layer 155c, a material that can withstand use at the fixing temperature and has excellent release properties with respect to the toner can be used. For example, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), PTFE (tetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoroethylene copolymer), PFEP (tetrafluoroethylene / hexafluoroethylene) A fluororesin such as a propylene fluoride copolymer) can be used.

  The guide plate 156 is a plate for guiding the fixing belt 155 that is driven to rotate in the rotating direction. The guide plate 156 is disposed inside the circulation path of the fixing belt 155 at a position facing the magnetic flux generator 170 via the fixing belt 155, is curved along the curvature of the fixing belt 155, and is driven to rotate. , The relative position between the fixing belt 155 and the magnetic flux generator 170 is regulated while guiding the fixing belt 155 in its circumferential direction. As a material constituting the guide plate 156, for example, a nonmagnetic resistance material such as copper or aluminum can be used.

  Instead of forming the magnetic shunt alloy layer 155a on the fixing belt 155, a magnetic shunt alloy layer 155a is provided on the guide plate 156 or the fixing roller 150, and the fixing belt has copper, nickel, etc. instead of the magnetic shunt alloy layer 155a. It is good also as providing the heat generating layer comprised by these. Even in such a configuration, similarly to the case where the magnetic shunt alloy layer 155 a is provided on the fixing belt 155, the guide plate 156 or the fixing roller 150 is electromagnetically heated to cause the curie through the guide plate 156 or the fixing roller 150. The temperature of the fixing belt is raised until the temperature is reached, and when the Curie temperature is reached, the temperature rise of the fixing belt can be suppressed.

  The pressure roller 160 is configured by laminating a release layer 163 around a cylindrical cored bar 161 via an elastic body layer 162, and is disposed outside the circulation path of the fixing belt 155. By pressing the fixing roller 150 with the pressure roller 160 from the outside of the fixing belt 155 via the fixing belt 155, a fixing having a predetermined width in the circumferential direction between the pressure roller 160 and the outer surface of the fixing belt 155. A nip 155n is formed.

The metal core 161 is a member that supports the pressure roller 160 and is made of a material having heat resistance and strength. As a material of the core metal 161, for example, aluminum, iron, stainless steel, or the like can be used.
The elastic body layer 162 is an elastic body such as silicone rubber or fluorine rubber, and is made of a material having high heat resistance within a thickness range of 1 to 20 mm. The release layer 163 is a layer for improving the release property between the pressure roller 160 and the recording sheet, and can be composed of the same material and thickness as the release layer 155c. As the size of the pressure roller 160, for example, a roller having an outer diameter of about 35 mm can be used.

The magnetic flux generator 170 includes a coil bobbin 171, a bottom core 172, an exciting coil 173, a core 174, and a cover 175, and a pressure roller sandwiching the fixing belt 155 outside the circulation path of the fixing belt 155. With reference to the position opposite to 160, the belt is disposed slightly upstream in the circumferential direction from here and along the width direction of the fixing belt 155.
The exciting coil 173 generates magnetic flux for electromagnetic induction heating of the magnetic shunt alloy layer 155 a of the fixing belt 155, and is wound around the coil bobbin 171. The alternating magnetic flux generated from the exciting coil 173 is guided to the fixing belt 155 by the core 174 and the bottom core 172, and penetrates the portion of the magnetic shunt alloy layer 155a of the fixing belt 155 that mainly faces the magnetic flux generating portion 170. An eddy current is generated in the portion to heat the magnetic shunt alloy layer 155a itself, and the temperature of the fixing belt 155 is increased.

As the fixing belt 155 is heated, the pressure roller 160 in contact with the fixing belt 155 at the fixing nip 155n is also heated. A central thermistor 180 for detecting the surface temperature of the fixing belt 155 is disposed near the center in the width direction of the fixing belt 155.
The control unit 60 acquires the surface temperature near the center of the fixing belt 155 based on the detection signal from the central thermistor 180, and excites the surface of the fixing belt 155 to the target temperature according to the acquired surface temperature. The amount of power supplied to the coil 173 is controlled.

[3] Configuration of Control Unit FIG. 4 is a diagram illustrating a relationship between the configuration of the control unit 60 and main components that are controlled by the control unit 60. The control unit 60 is a so-called computer, and as shown in the figure, a CPU (Central Processing Unit) 601, a communication interface (I / F) unit 602, a ROM (Read Only Memory) 603, a RAM (Random Access Memory). 604, an image data storage unit 605, a print job storage unit 606, a temperature control temperature storage unit 607, a frequency control table storage unit 608, a power control unit 609, a Curie temperature arrival determination unit 610, and the like.

  The communication I / F unit 602 is an interface for connecting to a LAN such as a LAN card or a LAN board. The ROM 603 controls a program for controlling the image processing unit 3, the paper feeding unit 4, the central thermistor 180, the IH power source 190, the image reading unit 7, the operation panel 8, and the like and a print job interruption control process described later. This program is stored. The CPU 601 controls the image processing unit 3, the paper feeding unit 4, the central thermistor 180, the IH power source 190, the image reading unit 7, the operation panel 8, and the like by executing various programs stored in the ROM. Then, a print job interruption control process described later is executed.

The RAM 604 is used as a work area when the CPU 601 executes a program.
The image data storage unit 605 stores image data for printing input via the communication I / F unit 602 and the image reading unit 7. The print job storage unit 606 stores a print job list indicating the correspondence between the print conditions of each print job input from the communication I / F unit 602 or the operation panel 8 and the identifiers of the print jobs. Each correspondence relationship is deleted from the print job list by the control unit 60 every time execution of the print job is completed. Here, the “printing condition” includes information such as the number of recording sheets to be printed, the designation of the size of the recording sheet, and the designation of the type of recording sheet (plain paper, cardboard, etc.).

  The temperature control temperature storage unit 607 stores each target temperature that is a target of temperature control of the fixing belt 155 in a print job interruption control process described later. Specifically, the fixing temperature (here, 180 ° C.) in the thermal fixing operation of the recording sheet of the plain paper is used. ), The fixing temperature (here, 210 ° C.) when the recording sheet type is thick paper and the recording sheet size is large (A3 size), the recording sheet type is thick paper, and the recording sheet size. Is stored in a small size (A4 size) (here, 200 ° C.) and a Curie temperature of the magnetic shunt alloy layer 155a (here, 220 ° C.).

  The frequency control table storage unit 608 stores a frequency control table. The “frequency control table” refers to the control frequency of the switching element of the IH power supply 190 for controlling the power supplied from the IH power supply 190 to the exciting coil 173, and the control frequency supplied from the IH power supply 190. When control is performed at the control frequency when the expected supply power (hereinafter referred to as “expected supply power”) and the surface temperature of the non-sheet passing area of the fixing belt 155 reach the Curie temperature. And a table showing a correspondence relationship with the supply power expected to be supplied from the IH power supply 190 (hereinafter referred to as “threshold supply power”).

  Here, the expected supply power corresponding to each control frequency is within a predetermined range (here, the control frequency of the switching element of the IH power supply 190 when the fixing belt 155 is controlled to the fixing temperature (about 180 ° C.)). In this case, the power is supplied to the exciting coil 173 when it is changed and set in the range of 44 to 52 kilohertz (kHz), and is measured and set in advance by the manufacturer of the printer 1.

  In addition, the threshold supply power corresponding to each control frequency is set to a sheet passing area when a small size recording sheet (here, plain paper, A4 size) is passed through the fixing belt 155. When the surface temperature of the IH power supply 190 is controlled to the fixing temperature (about 180 ° C.) and the surface temperature of the non-sheet passing area has reached the Curie temperature, the control frequency is set to a predetermined range in the switching element of the IH power source 190. This is the power supplied to the exciting coil 173 when it is changed within the range (here, within the range of 44 to 52 kilohertz (kHz)), and is measured and set in advance by the manufacturer of the printer 1.

  FIG. 5 is a diagram illustrating a specific example of the frequency control table. As shown in the figure, the threshold supply power is lower than the expected supply power. This is because when the surface temperature of the non-sheet passing area of the fixing belt 155 reaches the Curie temperature, the non-sheet passing area becomes a paramagnetic material, and the magnetic flux generated from the excitation coil 173 is not guided to the non-sheet passing area. Accordingly, the amount of magnetic flux that returns to the exciting coil 173 among the magnetic flux generated from the exciting coil 173 increases, so that the inductance of the exciting coil 173 increases, and as a result, between the voltage and current supplied from the IH power source 190. This is because a phase difference occurs and reactive power is generated.

  FIG. 6 shows a graph formed by plotting the corresponding relationship between the control frequency and the expected supply power and the control frequency and the threshold supply power in the frequency control table of FIG. The code | symbol 61 of the figure represents the graph which shows the correspondence of control frequency and estimated supply power, and the code | symbol 62 of the figure represents the graph which shows the correspondence of control frequency and threshold supply power. Further, reference numeral 63 in the figure denotes a control frequency and power supplied from the IH power source 190 to the exciting coil 173 (hereinafter referred to as “Curie temperature”) when the entire fixing belt 155 is controlled to the Curie temperature (about 220 ° C.). It represents a graph showing a correspondence relationship with “supplied power at arrival”).

Note that the frequency control table storage unit 608 may store the relational expressions corresponding to the respective graphs 61 and 62 shown in FIG. 6 instead of the table indicating the correspondence relation.
Further, the correspondence relationship of the graph indicated by reference numeral 62 may be calculated from the graphs indicated by reference numerals 61 and 63, respectively. Specifically, the power difference between the expected supply power and the supply power when the Curie temperature is reached at each control frequency is the non-sheet passing range (here, the length in the width direction of A3). The graph shown by reference numeral 62 may be created by correcting the power difference according to the ratio of the length in the width direction of A4.

  As shown in the figure, the value of the supply power corresponding to the control frequency is the lowest for the supply power when the Curie temperature is reached, indicating that the supply power decreases as the area that reaches the Curie temperature increases. ing. Using the frequency control table, the control unit 60 passes a recording sheet of a small size (here, plain paper, A4 size) through the fixing belt 155 and performs a heat fixing operation. In this case, it is determined whether or not the surface temperature of the non-sheet passing area of the fixing belt 155 has reached the Curie temperature.

The power control unit 609 of the control unit 60 calculates a supply power value necessary for setting the surface temperature to the target temperature according to the surface temperature near the center of the fixing belt 155 detected by the center thermistor 180. Then, the supply power value is notified to the CPU of the IH power supply 190, and the power necessary for setting the target temperature is supplied to the excitation coil 173.
The CPU of the IH power supply 190 determines a control frequency for controlling the switching element so that the supply power of the notified supply power value is supplied to the excitation coil 173, and supplies power to the excitation coil 173 at the determined control frequency. At the same time, the control unit 60 is notified of the determined control frequency.

  The Curie temperature arrival determination unit 610 of the control unit 60 refers to the frequency control table stored in the frequency control table storage unit 608, and the threshold supply power value corresponding to the control frequency notified from the CPU of the IH power supply 190. Is compared with the value of the supply power value notified to the CPU of the IH power supply 190. When the value of the supply power notified to the CPU of the IH power supply 190 is equal to or less than the value of the threshold supply power, the fixing belt 155 It is determined that the surface temperature of the non-sheet passing region has reached the Curie temperature.

  FIG. 7 is a circuit diagram showing an outline of the IH power supply 190. The IH power supply 190 includes a CPU 191, a switching element 192, a capacitor 193, a coil 194, a diode bridge 195, a voltage detection unit 196, a current detection unit 197, a coil 198, a noise filter 199, and the like. In the above configuration, the resonance circuit is formed by the capacitor 193, the coil 194, and the exciting coil 173.

The CPU 191 responds to a predetermined power supply instruction from the control unit 60 based on the detection result of the surface temperature of the fixing belt 155 by the central thermistor 180 (notification of a supply power value to set the surface temperature to the target temperature). A control frequency for controlling the switching element 192 is determined, and power is supplied to the excitation coil 173 at the determined control frequency.
The CPU 191 calculates the power supplied to the excitation coil 173 based on the detection result of the voltage and current supplied to the excitation coil 173 by the voltage detection unit 196 and the current detection unit 197, and the supplied power is indicated. The control frequency is adjusted so that the specified power supply value is obtained, and the control frequency for supplying the specified power supply value is determined.

The diode bridge 195 rectifies the alternating current from the alternating current power supply 200, and the noise filter 199 removes various noise components included in the power supplied from the alternating current power supply 200.
Returning to the description of FIG. 4, the image reading unit 7 is configured by an image input device such as a scanner, and reads information such as characters and figures described on a recording sheet such as paper to form image data. The operation panel 8 includes a plurality of input keys and a liquid crystal display unit, and a touch panel is laminated on the surface of the liquid crystal display unit. An instruction from the user is received by a touch input from the touch panel or a key input from an input key, and the control unit 60 is notified.

[4] Print Job Interruption Control Process Next, the operation of the print job interruption control process performed by the control unit 60 will be described. FIG. 8 is a flowchart showing the above operation. Here, all types of recording sheets are plain paper.
After the warm-up of the fixing device 5 is completed, the control unit 60 receives a print job instructing print processing of a small size (here, A4 size) recording sheet from the communication I / F unit 602 or the operation panel 8. Then, the small-size printing process related to the print job is started and the number of printed sheets is started (step S801), the print job list is acquired from the print job storage unit 606, and the print job list is referred to. (Step S802), it is determined whether there is a print job to be executed next to the print job being executed (Step S803).

If there is a print job to be executed next (step S803: YES), the control unit 60 refers to the print condition of the print job, and determines the size of the recording sheet (width of the fixing belt 155) related to the print job. It is determined whether the (direction size) is larger than the size of the recording sheet being printed (step S805).
If the determination result of step S805 is affirmative (step S805: YES), the control unit 60 refers to the frequency control table stored in the frequency control table storage unit 608, and fixes the fixing belt 155 to the IH power supply 190. , The threshold power supply value corresponding to the control frequency notified from the IH power supply 190 in response to the notification of the power supply value necessary for maintaining the surface temperature at the fixing temperature (here, 180 ° C.). Then, by comparing the value of the supplied power value notified to the IH power supply 190, it is determined whether or not the surface temperature of the non-paper area of the fixing belt 155 has reached the Curie temperature (step S806).

  When the surface temperature of the non-paper area of the fixing belt 155 reaches the Curie temperature (step S806: YES), the control unit 60 inhibits execution of the next print job when the currently executed print job is completed. The execution suppression flag for determining whether or not to perform is set to “on” indicating that the execution is to be suppressed, and the number of prints of the print job being printed and the number of prints indicated by the print condition of the print job Based on the above, the remaining number of prints (P) in the print job is calculated (step S808), and it is determined whether P is less than the number of sheets that can reach the Curie temperature (P0) (step S809).

  Here, “the number of sheets that can reach the Curie temperature” is a limit temperature (here, 10 ° C., hereinafter referred to as “Δt”) at which gloss unevenness does not occur during the thermal fixing process for one sheet in the printing process. When the surface temperature of the fixing belt 155 is raised, it reaches the Curie temperature of the magnetic shunt alloy layer 155a (here, 220 ° C.) from the fixing temperature (here, 180 ° C.). It means the number of required prints (here, 4).

  Therefore, if P is equal to or greater than the number of sheets that can reach the Curie temperature, the surface temperature of the fixing belt 155 is increased by the limit temperature (Δt) during one thermal fixing process (in this case, the fixing belt 155 is not turned on). (Since the surface temperature of the paper region has already reached the Curie temperature, the non-sheet passing region is not heated, and only the surface temperature of the sheet passing region of the fixing belt 155 is increased by Δt.) As a result, the temperature difference in the surface temperature between the non-sheet-passing area and the sheet-passing area of the fixing belt 155 that has reached the Curie temperature can be eliminated before the print job being printed is completed. Even if the print job is a large size (here, A3 size), gloss unevenness can be prevented from occurring even if the print job is continuously executed.

  When P is less than the Curie temperature reachable sheet number (P0) (step S809: YES), the control unit 60 executes an inter-job printing process interruption temperature difference adjustment process described later (step S810), and P is the Curie temperature. If it is equal to or greater than the reachable number (P0) (step S809: NO), the control unit 60 executes an inter-job printing process non-interrupt temperature difference adjustment process described later (step S811).

When the determination result in step S806 is negative (step S806: NO) and the print job that was being printed is completed (step S807: YES), the control unit 60 performs the process before executing the next print job. The process for adjusting the temperature difference of the surface temperature between the sheet passing area and the non-sheet passing area of the fixing belt 155 is suppressed, and the next print job is executed (step S812).
If the determination result of step S805 is negative (step S805: NO), the control unit 60 proceeds to the process of step S812, and the determination result of step S803 is negative (step S803: NO). ) When the print job that was being printed ends (step S804: YES), the control unit 60 ends the operation of the print job interruption control process.

  Next, the operation of the inter-job printing process interruption temperature difference adjustment process performed by the control unit 60 will be described. FIG. 9 is a flowchart showing the above operation. The controller 60 controls the surface of the fixing belt 155 by the limit temperature (Δt) for each recording sheet of the remaining number (P) of unprocessed print sheets in the print job being executed, while performing one thermal fixing process. By controlling the surface temperature of the fixing belt 155 using the IH power source 190 so as to raise the temperature, the surface temperature of the sheet passing area of the fixing belt 155 is raised (step S901).

  When the currently executed print job is completed (step S902: YES), the control unit 60 refers to the execution suppression flag. Since the execution inhibition flag is set to “ON” in the process of step S808, the control unit 60 interrupts the printing process, inhibits execution of the next print job (step S903), and the fixing belt 155. Is continued until the surface temperature (t) of the sheet reaches the Curie temperature (t0) (step S904).

When the surface temperature (t) of the fixing belt 155 reaches the Curie temperature (t0) (step S905: YES), the control unit 60 indicates that the execution inhibition of the next print job has been released. “Off” is set, the suppression of execution of the next print job is canceled, and the print processing of the next print job is started (step S906).
Then, the control unit 60 controls the amount of power supplied from the IH power supply 190 to the exciting coil 173 so that the surface temperature of the fixing belt 155 is lowered by the limit temperature (Δt) during the thermal fixing process for each sheet. (Step S907).

The control unit 60 repeats the process of step 907 until the surface temperature (t) of the fixing belt 155 reaches the target fixing temperature (here, assumed to be 180 ° C.) (step S908: YES).
FIG. 10 is a diagram schematically showing how the temperature of the surface temperature (t) of the fixing belt 155 is adjusted by executing the above-described inter-job printing process interruption temperature difference adjustment process. This figure shows an example in which the number of remaining prints (P) of the print job being printed is one. As shown in the figure, since the remaining number (P) is one before the end of the print job in the printing process, the surface temperature of the sheet passing area of the fixing belt 155 until the end of the print job. Is raised from the target fixing temperature (180 ° C.) by Δt (10 ° C.).

  At this time, since the surface temperature of the sheet passing area of the fixing belt 155 is 190 ° C. and has not reached the Curie temperature (220 ° C.), the execution of the next print job is suppressed until the Curie temperature is reached. Is suppressed, the temperature raising operation of the surface temperature of the sheet passing area of the fixing belt 155 is continued. In this case, the temperature increase rate is increased by the temperature increase rate during the heat fixing process (Δt (10 ° C.) during one heat fixing process) in order to advance the time to reach the Curie temperature (220 ° C.). The temperature is controlled by the controller 60 so as to be faster.

  When the surface temperature of the sheet passing area of the fixing belt 155 reaches the Curie temperature (220 ° C.), the execution inhibition of the next print job (print job with four prints) is canceled, and the print processing of the next print job is performed. Until the surface temperature of the fixing belt 155 returns to the original target fixing temperature (180 ° C.), the surface temperature of the fixing belt 155 is increased by Δt (10 ° C.) during each thermal fixing process. The temperature is controlled by the control unit 60 so as to descend.

  As described above, in the print job interruption control process, the surface temperature of the fixing belt 155 is raised to some extent within a temperature range in which gloss unevenness does not occur until the current print job is finished, and then the next The temperature raising operation is continued between the print jobs, and the temperature difference between the surface temperatures of the fixing belt 155 between the paper passing area and the non-paper passing area is eliminated. Accordingly, the time can be shortened, and the productivity of the heat fixing job execution can be increased.

  Further, after the surface temperature of the fixing belt 155 is raised to the Curie temperature and the temperature difference between the surface temperature between the paper passing area and the non-paper passing area is eliminated, uneven glossiness is generated during execution of the next print job. The temperature is controlled so that the surface temperature of the fixing belt 155 falls to the original target fixing temperature in a temperature range where no occurrence occurs, so that the heat fixing operation in the print job is performed at a temperature higher than necessary, and the power is excessive. It is possible to effectively prevent consumption.

  Next, the operation of the inter-job printing process non-interrupted temperature difference adjustment process performed by the control unit 60 will be described. FIG. 11 is a flowchart showing the above operation. The controller 60 controls the surface of the fixing belt 155 by the limit temperature (Δt) for each recording sheet of the remaining number (P) of unprocessed print sheets in the print job being executed, while performing one thermal fixing process. By controlling the surface temperature of the fixing belt 155 using the IH power source 190 so as to raise the temperature, the surface temperature of the sheet passing area of the fixing belt 155 is raised (step S1101).

  When the surface temperature (t) of the fixing belt 155 (surface temperature of the sheet passing area) reaches the Curie temperature (t0) (step S1102: YES), the control unit 60 sets the execution suppression flag to “off” and Temperature control is performed so that the surface temperature of the fixing belt 155 is maintained at the Curie temperature (t0) until the print job being printed is completed (steps S1103 and S1104: NO).

  When the print job being executed ends (step S1104: YES), the control unit 60 refers to the execution suppression flag. Since the execution suppression flag is set to “OFF” in the process of step S1103, the control unit 60 starts the printing process of the next print job (step S1105), and performs one thermal fixing process for each sheet. During the process, the power supply amount from the IH power source 190 to the exciting coil 173 is controlled so as to lower the surface temperature of the fixing belt 155 by the limit temperature (Δt) (step S1106).

The controller 60 repeats the process of step 1106 until the surface temperature (t) of the fixing belt 155 reaches the target fixing temperature (here, 180 ° C.) (step S1107: YES).
FIG. 12 is a diagram schematically illustrating how the temperature of the surface temperature (t) of the fixing belt 155 is adjusted by executing the above-described inter-job printing process non-interrupt temperature difference adjustment process. This figure shows an example in which the number of remaining prints (P) of a print job being printed is four. As shown in the figure, there are four remaining sheets (P) by the time the print job being printed is completed, so the surface temperature of the sheet passing area of the fixing belt 155 is increased by the end of the print job. Each time one sheet thermal fixing process is performed, Δt is raised from the target fixing temperature (180 ° C.) by 4 × Δt (40 ° C.) while four sheets of thermal fixing processes are performed.

  As a result, the surface temperature of the sheet passing area of the fixing belt 155 is raised to the Curie temperature (220 ° C.) while the heat fixing process of the print job being executed is being performed, so the next print job is executed. The printing process of the next print job is started continuously without being suppressed. Then, control is performed so that the surface temperature of the fixing belt 155 is lowered by Δt while the thermal fixing process for each sheet is performed until the surface temperature of the fixing belt 155 returns to the original target fixing temperature (180 ° C.). The temperature is controlled by the unit 60.

  As described above, in the inter-job printing process non-interrupt temperature difference adjustment process, the surface temperature of the fixing belt 155 is raised within a temperature range in which gloss unevenness does not occur until the current print job is completed. As a result, the temperature difference in the surface temperature between the sheet passing area and the non-sheet passing area in the fixing belt 155 is eliminated, so that the productivity of the heat fixing job execution is improved without suppressing the execution of the next print job. be able to.

Further, after the surface temperature of the fixing belt 155 is raised to the Curie temperature and the temperature difference between the surface temperature between the paper passing area and the non-paper passing area is eliminated, uneven glossiness is generated during execution of the next print job. The temperature is controlled so that the surface temperature of the fixing belt 155 falls to the original target fixing temperature in a temperature range where no occurrence occurs, so that the heat fixing operation in the print job is performed at a temperature higher than necessary, and the power is excessive. It is possible to effectively prevent consumption.
(Modification)
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

  (1) In this embodiment, when the non-paper area of the fixing belt 155 reaches the Curie temperature, the process of adjusting the temperature difference between the surface temperatures of the fixing belt 155 between the paper passing area and the non-paper passing area. However, when the non-paper area of the fixing belt 155 reaches at least the temperature at which gloss unevenness occurs (the temperature difference between the surface temperature of the non-paper passing area and the surface temperature (fixing temperature) of the paper passing area is When the temperature exceeds a limit temperature (Δt) at which gloss unevenness does not occur), the temperature difference between the two may be adjusted.

  Specifically, a temperature sensor is provided in the vicinity of the non-sheet passing area of the fixing belt 155, and the control unit 60 monitors the surface temperature of the fixing belt 155 in the non-sheet passing area. In the control process, instead of performing the determination process in step S806, whether or not the surface temperature of the non-sheet passing area exceeds (target fixing temperature + Δt) (“non-sheet passing area” and “sheet passing area in the fixing belt 155). 8), the process of Steps S808 to 811 in FIG. 8 is performed.

Further, in steps 810 and 811, not when “t has reached t0” (step S 905: YES, step S 1102: YES), but when “the above temperature difference is within the limit value”, steps S 906- The processing in step S908 and the processing in steps S1103 to S1107 are performed.
As a result, when the temperature difference between the two reaches a temperature difference that causes uneven glossiness, the temperature difference can be quickly adjusted to prevent the occurrence of uneven glossiness due to the temperature difference.

  (2) In this embodiment, the surface temperature of the fixing belt is increased or decreased during one thermal fixing process in each of the processes of Step S901, Step S907 of FIG. 9, Step S1101, and Step S1106 of FIG. The temperature to be uniformly set is Δt, but the surface temperature may be increased or decreased by changing the temperature increase or decrease within a range not exceeding the limit temperature.

  (3) In the present embodiment, the Curie temperature arrival determination unit 610 of the control unit 60 causes the surface temperature of the non-sheet passing region of the fixing belt 155 to reach the Curie temperature based on the control frequency notified from the CPU 191 of the IH power source. However, instead of performing the determination via the Curie temperature arrival determination unit 610, a temperature sensor (for example, a thermistor) is disposed in the non-sheet passing region of the fixing belt 155. The surface temperature of the non-sheet passing area may be detected by the temperature sensor to determine whether or not the surface temperature of the non-sheet passing area has reached the Curie temperature.

  (4) In the present embodiment, in the print job interruption control process of FIG. 8, when the non-paper area of the fixing belt 155 has not reached the Curie temperature, the temperature adjustment of the fixing belt 155 is not performed. The recording sheet type of the next print job is a thick sheet recording sheet that is thicker than the recording sheet of the print job being executed immediately before the print job. When it is necessary to perform heat fixing with fixing at a higher temperature than the case, the temperature of the fixing belt 155 may be raised to control so as not to cause fixing failure.

  FIG. 13 is a flowchart showing a modified example of the operation of the print job interruption control process executed together with the temperature adjustment. In FIG. 8, the same processing as the print job interruption control processing shown in FIG. 8 is assigned the same number as the processing step number in FIG. 8, and the description is omitted. For the processing step number, the display of the processing content is omitted.

  Hereinafter, processing different from the processing content of FIG. 8 will be described. When the determination result of step S805 is affirmative (step S805: YES), the control unit 60 refers to the print condition of the print job being printed and the print condition of the print job to be executed next, It is determined whether or not the recording sheet type (paper type) of the print job to be executed next is thick paper that is thicker than the recording sheet (plain paper recording sheet) of the print job being printed (step). S1301).

  If it is cardboard (step S1301: YES), the control unit 60 sets the execution suppression flag to “ON” (step S1302), and the number of print jobs being printed and the print job print conditions. The remaining number of prints (P) in the print job is calculated based on the number of prints indicated by (Step S1303), and the surface temperature of the non-paper area of the fixing belt 155 reaches the Curie temperature in the same manner as in Step S806. It is determined whether or not (step S1304).

  When the surface temperature of the non-paper area of the fixing belt 155 reaches the Curie temperature (step S1304: YES), the control unit 60 determines whether P is less than the number of sheets that can reach the Curie temperature (P0) ( Step S1305). If the determination result in step S1305 is affirmative (step S1305: YES), the control unit 60 executes an inter-job printing process interruption cardboard temperature difference adjustment process 1 described later (step S1306). If the determination result of step S1305 is negative (step S1305: NO), the control unit 60 executes an inter-job printing process non-interrupting cardboard large temperature difference adjustment process 1 described later (step S1307).

In step S1304, when the surface temperature of the non-paper area of the fixing belt 155 has not reached the Curie temperature (step S1304: NO), the control unit 60 has P less than the number of sheets that can reach the thick paper large fixing temperature (P1). It is determined whether or not (step S1308).
Here, “the number of sheets capable of reaching the large fixing temperature of the thick paper” means that when the surface temperature of the fixing belt 155 is increased by a limit temperature (Δt) at which gloss unevenness does not occur during the thermal fixing process for one sheet, From the fixing temperature (here, 180 ° C.) of the recording sheet of the print job being executed to the fixing temperature (here, 210 ° C.) for a large-size cardboard (here, A3 size). It means the number of printed sheets required to reach (here, 3).

  If the determination result in step S1308 is affirmative (step S1308: YES), the control unit 60 executes an inter-job printing process interrupted cardboard temperature difference adjustment process 2 (step S1309), which will be described later, and step S1308. If the determination result is negative (step S1308: NO), the control unit 60 executes the inter-job printing process non-interrupting cardboard large temperature difference adjustment process 2 described later (step S1310).

  On the other hand, when the determination result in step S805 is negative (step S805: NO), the control unit 60 performs the type of recording sheet (paper type) of the print job to be executed next in the same manner as in step S1301. Is determined to be thick paper thicker than the recording sheet of the print job being printed (step S1311), and if it is thick paper (step S1311: YES), the control unit 60 executes the execution suppression flag. Is set to “ON” (step S1312), and the remaining number of prints (P) in the print job is calculated based on the number of prints of the print job being printed and the number of prints indicated by the print conditions of the print job. (Step S1313).

  Next, the control unit 60 determines whether or not the calculated P is less than the number of sheets that can be reached by the small cardboard fixing temperature (P2) (step S1314). Here, “the number of sheets capable of reaching the small fixing temperature of the thick paper” means that when the surface temperature of the fixing belt 155 is increased by a limit temperature (Δt) at which gloss unevenness does not occur during the thermal fixing process for one sheet, From the fixing temperature (here, 180 ° C.) of the recording sheet of the print job being executed to the fixing temperature (here, 200 ° C.) for a small paper size (here, A4 size). It means the number of printed sheets required to reach (here, 2).

  If the determination result of step S1314 is affirmative (step S1314: YES), the control unit 60 executes an inter-job printing process interruption cardboard small temperature difference adjustment process (step S1315), which will be described later. If the determination result is negative (step S1314: NO), the control unit 60 executes an inter-job printing process non-interrupting cardboard small temperature difference adjustment process, which will be described later (step S1316).

Next, the operation of the inter-job printing process interruption thick paper large temperature difference adjustment process 1 performed by the control unit 60 will be described. FIG. 14 is a flowchart showing the above operation. The processing from step S1401 to step S1406 is the same as the processing from step S901 to step S906 in the operation of the inter-job printing process interruption temperature difference adjustment process in FIG.
After performing the process of step S1406, the control unit 60 controls the amount of power supplied from the IH power source 190 to the exciting coil 173 so that the surface temperature (t) of the fixing belt 155 is maintained at the Curie temperature (t0). Thus, the temperature is controlled (step S1407).

  Next, the operation of the inter-job printing process uninterrupted cardboard large temperature difference adjustment process 1 performed by the control unit 60 will be described. FIG. 15 is a flowchart showing the above operation. The processing from step S1501 to step S1505 is the same as the processing from step S1101 to step S1105 in the operation of the inter-job printing processing non-interrupting temperature difference adjustment processing in FIG. Further, the processing in step S1506 is the same as the processing in step S1407 in FIG.

Next, the operation of the inter-job printing process interruption temperature difference adjustment process 2 performed by the control unit 60 will be described. FIG. 16 is a flowchart showing the above operation. The processing in steps S1601 to S1603 and the processing in step S1606 are the same as those in steps S901 to S903 and S906 in FIG.
In step S1604, the control unit 60 continues the temperature raising operation until the surface temperature (t) of the fixing belt 155 (surface temperature of the sheet passing region) reaches the fixing temperature (t1) for large paper, When the surface temperature (t) of the fixing belt 155 reaches the fixing temperature (t1) for large paper (step S1605: YES), the process proceeds to step S1606, and then, in step S1607, the IH power source 190 supplies the exciting coil 173. The temperature of the fixing belt 155 is controlled so that the surface temperature of the fixing belt 155 is maintained at the fixing temperature (t1) for large paper.

  Next, the operation of the inter-job printing process uninterrupted cardboard large temperature difference adjustment process 2 performed by the control unit 60 will be described. FIG. 17 is a flowchart showing the above operation. The processing in step S1701, step S1704, and step S1705 is the same as the processing in step S1101, step S1104, and step S1105 of the inter-job printing process non-interrupt temperature difference adjustment process in FIG.

  In step S1702, when the surface temperature (t) of the sheet passing area of the fixing belt 155 reaches the fixing temperature (t1) for thick paper (step S1702: YES), the control unit 60 sets the execution suppression flag to “OFF”. The temperature is controlled so that the surface temperature (t) of the sheet passing area of the fixing belt 155 is maintained at the fixing temperature (t1) for thick paper until the print job being printed is completed (steps S1703 and S1704). : NO). Further, the processing in step S1706 is the same as the processing in step S1607 in the operation of the inter-job printing process interruption cardboard temperature difference adjustment process 2 in FIG.

Next, the operation of the inter-job printing process interruption thick paper small temperature difference adjustment process performed by the control unit 60 will be described. FIG. 18 is a flowchart showing the above operation. Since the processes in steps S1801 to S1803 and the processes in step S1806 are the same as those in steps S901 to S903 and S906 in FIG.
In step S1804, the control unit 60 continues the temperature raising operation until the surface temperature (t) of the fixing belt 155 (surface temperature of the sheet passing area) reaches the fixing temperature (t2) for small cardboard, When the surface temperature (t) of the fixing belt 155 reaches the fixing temperature (t2) for small cardboard (step S1805: YES), the process proceeds to step S1806, and then, in step S1807, the IH power source 190 supplies the exciting coil 173. The temperature of the fixing belt 155 is controlled so that the surface temperature of the fixing belt 155 is maintained at the fixing temperature (t2) for the small cardboard.

  Next, the operation of the inter-job printing process uninterrupted cardboard small temperature difference adjustment process performed by the control unit 60 will be described. FIG. 19 is a flowchart showing the above operation. The processing in step S1901, step S1904, and step S1905 is the same as the processing in step S1101, step S1104, and step S1105 of the inter-job printing process non-interrupt temperature difference adjustment process in FIG.

  In step S1902, when the surface temperature (t) of the sheet passing area of the fixing belt 155 reaches the fixing temperature (t2) for the small cardboard (step S1902: YES), the control unit 60 sets the execution suppression flag to “OFF”. The temperature control is performed so that the surface temperature (t) of the sheet passing area of the fixing belt 155 is maintained at the fixing temperature (t2) for small paper until the print job being printed is completed (steps S1903 and S1904). : NO). Further, the processing in step S1907 is the same as the processing in step S1807 in the operation of the inter-job printing process interruption thick paper small temperature difference adjustment process in FIG.

  The present invention relates to a printer, a copying machine, or the like that heat-fixes an unfixed image on a recording sheet by using a heating element including a magnetic shunt alloy layer that generates heat by electromagnetic induction and has a Curie temperature higher than a fixing temperature. In particular, the image forming apparatus can be used as a technique for preventing occurrence of gloss unevenness due to a temperature difference between a sheet passing area and a non-sheet passing area that occurs when a recording sheet having a predetermined width is continuously passed.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y-3K Image creation part 4 Paper feed part 5 Fixing device 7 Image reading part 8 Operation panel 10 Exposure part 11 Intermediate transfer belt 12 Driven roller 13 Drive roller 21, 35Y Cleaner 31Y Photosensitive drum 32Y Charger 33Y Developer 34Y Primary transfer roller 41 Paper feed cassette 42 Feed roller 43 Transport path 44 Timing roller 45 Secondary roller roller 46 Secondary transfer position 60 Control unit 71 Discharge roller 72 Discharge tray 150 Fixing roller 155 Fixing belt 156 Guide plate 160 Addition Pressure roller 170 Magnetic flux generator 180 Central thermistor 190 IH power supply

Claims (8)

An unfixed image on a recording sheet using a heating element that includes a magnetic shunt alloy layer that generates heat by electromagnetic induction and has a Curie temperature higher than the fixing temperature. The temperature difference between the temperature of the heating element corresponding to the sheet passing area and the temperature of the area corresponding to the non-sheet passing area in the heating element during the execution of the print job causes the gloss unevenness due to the latter temperature increase. An image forming apparatus that, when an allowable limit value is exceeded, suppresses execution of thermal fixing of the next print job until the temperature difference falls within the limit value after completion of thermal fixing of the print job. ,
Determining means for determining whether the temperature difference has exceeded the limit value due to a temperature rise in the area corresponding to the non-sheet passing area during execution of the print job;
When the limit value is exceeded, the temperature of the area corresponding to the paper passing area is increased by raising the heating element from the fixing temperature within a period until the print job being executed is completed. Temperature control means for raising the temperature at a faster temperature rise rate than the area corresponding to the non-sheet passing area;
When the temperature difference returns within the limit value within a period until the thermal fixing of the print job is completed due to the temperature rise by the temperature control means, the execution of the thermal fixing of the next print job is suppressed. Releasing means for releasing
An image forming apparatus comprising: If the temperature difference does not return within the limit value within a period until the thermal fixing of the print job is completed, the temperature control unit may determine the temperature after the thermal fixing of the print job is completed. Further heating the heating element until the difference returns within the limit,
The canceling unit cancels the suppression of the thermal fixing of the next print job when the temperature difference returns to the limit value by further raising the temperature of the heating element. The image forming apparatus according to claim 1. Said temperature control means, to said temperature difference is within the limit value, within a period of up to heat the fixing of the print job is completed, every time the thermal fixing is performed on a recording sheet, the thermal fixing is performed The temperature of the heating element is raised stepwise so that the temperature rise amount during a period does not exceed a limit temperature at which gloss unevenness does not occur during the thermal fixing process for one sheet. The image forming apparatus according to 2. When the temperature difference returns within the limit value , the temperature control means performs thermal fixing on the recording sheet within a period from the start of thermal fixing of the next print job until the end of the thermal fixing. The temperature of the heating element is gradually increased so that the amount of temperature decrease during each thermal fixing does not exceed the limit temperature at which gloss unevenness does not occur during the thermal fixing process for each sheet. The image forming apparatus according to claim 1, wherein the image forming apparatus is lowered until the fixing temperature is reached. A thickness specifying means for specifying the thickness of the recording sheet of the print job;
It said temperature control means, the thickness of the recording sheet of the print job in execution, if thinner than the thickness of the recording sheet in the next print job, in the period until the thermal fixing of a print job in execution is completed, the recording Each time the sheet is heat-fixed , the temperature rise during each heat-fixing period is stepwise so that it does not exceed the limit temperature at which gloss unevenness does not occur during the heat-fixing process for one sheet. Heating up the heating element;
The release means is configured to cause the temperature of the heating element to be higher than the fixing temperature related to the print job being executed within a period until the thermal fixing of the print job is completed due to the temperature rise by the temperature control means. 5. The deterrence of execution of thermal fixing of the next print job is canceled when a predetermined temperature suitable for thermal fixing of the recording sheet of the print job is reached. Image forming apparatus. If the temperature of the heating element does not reach the predetermined temperature within a period until the thermal fixing of the print job is completed, the temperature control means sets the temperature of the heating element to the predetermined temperature. Further heating the heating element until
6. The release unit according to claim 5, wherein when the temperature of the heating element that has been further increased reaches the predetermined temperature, the suppression of execution of thermal fixing of the next print job is canceled. Image forming apparatus. The said determination means determines that the said temperature difference exceeded the said limit value, when the temperature of the area | region corresponding to the said non-sheet passing area | region reaches Curie temperature. The image forming apparatus described in 1. A size specifying means for specifying the size of the recording sheet of the print job;
The temperature control unit suppresses a temperature raising operation for raising the temperature of the heating element from a fixing temperature when the size of the recording sheet of the print job being executed and the next print job is the same,
The image forming apparatus according to claim 1, wherein the canceling unit cancels suppression of execution of thermal fixing of a next print job.

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