Image forming device

Abstract

To reduce the possibility of the occurrence of a fixing failure.SOLUTION: An image forming apparatus comprises a heat generating unit, a pressing unit, a detection unit, a control unit, and a setting unit. The heat generating unit generates heat to heat a sheet conveyed in a conveyance direction over the entire area in a direction orthogonal to the conveyance direction. The pressing unit applies pressure to the sheet heated by the heat generating unit over the entire area in the direction orthogonal to the conveyance direction. The detection unit detects the temperature of the pressing unit. The control unit controls the heat generating unit to bring the temperature detected by the detection unit closer to a control temperature. The setting unit sets, before the start of image formation related to one job, one of a plurality of candidate temperature different from each other as the control temperature based on the number of images to be formed and the size of sheets to be used in the job.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] An embodiment of the present invention relates to an image forming apparatus. [Background technology]

[0002] For example, in an electrophotographic image forming apparatus, a heated roller is used to fix a developer attached to a sheet of paper. If the pressure applied by this roller to the paper and developer is reduced, poor fusing may occur. In view of these circumstances, it has been desired to reduce the possibility of poor fixing occurring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-242982 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an image forming apparatus capable of reducing the possibility of poor fixing. [Means for solving the problem]

[0005] The image forming apparatus of the embodiment includes a heating section, a pressing section, a detection section, a control section, and a setting section. The heating section generates heat to heat the paper being transported in the transport direction over the entire area in a direction perpendicular to the transport direction. The pressing section applies pressure to the paper heated by the heating section over the entire area in the direction perpendicular to the transport direction. The detection section detects the temperature of the pressing section. The control section controls the heating section so that the temperature detected by the detection section approaches a control temperature. Before image formation for one job begins, the setting section: (1) Number of images formed in the job is a predetermined number of sheets for bulk printing, (2) Paper to be used and the paper is a narrow paper that is predetermined as a narrow paper. When either one of the two conditions is not satisfied, a predetermined first temperature is set as the control temperature, and when both of the two conditions are satisfied, a predetermined second temperature different from the first temperature is set as the control temperature. is set as the control temperature. [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is a diagram illustrating an outline of the mechanical configuration of an MFP according to an embodiment. [Diagram 2] 2 is a block diagram illustrating a configuration related to control of the MFP illustrated in FIG. 1. [Diagram 3] 3 is a block diagram showing a main circuit configuration of a system controller shown in FIG. 2. [Figure 4] 4 is a flowchart of a print control process performed by a processor shown in FIG. 3. [Diagram 5] 2 is a graph showing the results of measuring the temperature of the fixing belt shown in FIG. 1 at a plurality of positions in the longitudinal direction of the fixing belt. [Figure 6] 2 is a diagram showing the results of measuring the temperature of the press roller shown in FIG. 1 at a plurality of positions in the longitudinal direction of the press roller. [Figure 7] 2 is a graph showing the results of measuring the temperature of the fixing belt shown in FIG. 1 at a plurality of positions in the longitudinal direction of the fixing belt. [Figure 8] 2 is a diagram showing the results of measuring the temperature of the press roller shown in FIG. 1 at a plurality of positions in the longitudinal direction of the press roller. [Figure 9] 2 is a diagram showing the relationship between the control temperature and the print speed and the temperature difference depending on the position in the longitudinal direction of the press roller shown in FIG. 1. [Figure 10] 2 is a diagram showing the relationship between the temperature difference and the outer diameter difference depending on the position in the longitudinal direction of the press roller shown in FIG. 1. [Figure 11] FIG. 11 is a diagram showing the relationship between the control temperature, the print speed, and the offset level. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, an embodiment will be described with reference to the drawings. In the following embodiment, an MFP (multi-function peripheral) including an image forming device will be described as an example. The contents of the various operations and various processes described below are merely examples, and it is possible to change the order of some of the operations and processes, omit some of the operations and processes, or add other operations and processes as appropriate.

[0008] First, the configuration of the MFP according to this embodiment will be described. FIG. 1 is a diagram illustrating a schematic mechanical configuration of an MFP 100 according to an embodiment. As shown in FIG. 1, the MFP 100 includes a scanner 101 and a printer 102 .

[0009] The scanner 101 reads an image of an original document and generates image data corresponding to the original document. The scanner 101 uses an image sensor such as a CCD (charge-coupled device) line sensor to generate image data according to a reflected light image from a reading surface of the original document. The scanner 101 scans an original document placed on a platen with an image sensor that moves along the original document. Alternatively, the scanner 101 scans an original document conveyed by an ADF (auto document feeder) with a fixed image sensor.

[0010] The printer 102 forms an image on a medium on which the image is to be formed by an electrophotographic method. The medium is typically printing paper such as cut paper. In the following, therefore, the description will be given assuming that printing paper is used as the medium. However, the medium may be a paper sheet material other than cut paper, or a sheet material made of a material other than paper, such as resin, may be used. The printer 102 has a color printing function for printing a color image on printing paper, and a monochrome printing function for printing a monochrome image on printing paper. The printer 102 forms a color image by forming elemental images using developers of three colors, for example, yellow, magenta, and cyan, or four colors including the above and black, by superimposing them. The printer 102 also forms a monochrome image by using a black developer, for example. The developer is, for example, a toner. The developer may include, for example, a toner and a carrier. However, the printer 102 may have only one of the color printing function and the monochrome printing function.

[0011] In the configuration example shown in FIG. 1, the printer 102 includes a paper feed unit 1, a print engine 2, a fixing unit 3, an ADU (automatic double-sided unit) 4, and a paper discharge tray 5. The paper feed unit 1 includes paper feed cassettes 10-1, 10-2, and 10-3, pickup rollers 11-1, 11-2, and 11-3, conveying rollers 12-1, 12-2, and 12-3, a conveying roller 13, and a registration roller 14.

[0012] The paper feed cassettes 10-1, 10-2, and 10-3 store print paper in a stacked state. The print paper stored in each of the paper feed cassettes 10-1, 10-2, and 10-3 may be different types of print paper with different sizes and materials, or may be the same type of print paper. The paper feed unit 1 may also include a manual feed tray. Pickup rollers 11-1, 11-2, and 11-3 pick up print paper one by one from each of paper feed cassettes 10-1, 10-2, and 10-3, and feed the picked up print paper to transport rollers 12-1, 12-2, and 12-3. The conveying rollers 12-1, 12-2, and 12-3 convey the print paper fed from the pickup rollers 11-1, 11-2, and 11-3 to the conveying rollers 13 via a conveying path formed by a guide member (not shown) and the like.

[0013] The conveying rollers 13 further convey the print paper fed from any one of the conveying rollers 12-1, 12-2, and 12-3, and feed it to the registration rollers 14. The registration rollers 14 correct the skew of the print paper and adjust the timing at which the print paper is sent to the print engine 2. The number of sets of the paper feed cassette, the pickup roller, and the transport roller is not limited to three, and any number of sets may be provided. Also, if a manual feed tray is provided, it is not necessary to provide any set of the paper feed cassette and the pickup roller and the transport roller that form a pair with it.

[0014] The print engine 2 includes a belt 20, support rollers 21, 22, and 23, image forming units 24-1, 24-2, 24-3, and 24-4, an exposure unit 25, and a transfer roller . Belt 20 is endless and is supported by support rollers 21, 22, and 23 so as to maintain the state shown in FIG. 1. Belt 20 rotates counterclockwise in FIG. 1 with the rotation of support roller 21. Belt 20 temporarily carries a developer image to be formed on print paper on its outer surface (hereinafter referred to as the image carrying surface). For example, semiconductive polyimide is used for belt 20 in terms of heat resistance and abrasion resistance. The movement of the image carrying surface with the rotation of belt 20 realizes so-called sub-scanning, and the movement direction of the image carrying surface is also called the sub-scanning direction.

[0015] Each of the image forming units 24-1 to 24-4 includes a photoconductor, a charger, a developer, a transfer roller, and a cleaner, and has a known structure for forming an image by electrophotography in cooperation with the exposure unit 25. The image forming units 24-1 to 24-4 are arranged along the belt 20 with the axial directions of the respective photoconductors parallel to each other. The image forming units 24-1 to 24-4 have the same structure and operation, except for the color of the developer used. The image forming unit 24-1 forms an element image using, for example, a black developer. The image forming unit 24-2 forms an element image using, for example, a cyan developer. The image forming unit 24-3 forms an element image using, for example, a magenta developer. The image forming unit 24-4 forms an element image using, for example, a yellow developer. The image forming units 24-1 to 24-4 make the element images of each color overlap each other on the image carrying surface of the belt 20. As a result, the image forming units 24-1 to 24-4 form a color image by superimposing the element images of each color on the image bearing surface of the belt 20 at the time when the belt 20 passes the image forming unit 24-1. Although not shown in the figure, developer containers that contain developers of each color are arranged, for example, in the spaces between the belt 20.

[0016] The exposure unit 25 exposes the photoconductors of the image forming units 24-1 to 24-4 according to image data representing elemental images of each color. A laser scanner or an LED (light emitting diode) head is used as the exposure unit 25. If a laser scanner is used, the exposure unit 25 includes, for example, a semiconductor laser element, a polygon mirror, an imaging lens system, and a mirror. In this case, the exposure unit 25 selectively makes the laser beam emitted from the semiconductor laser element according to the image data incident on each of the photoconductors of the image forming units 24-1 to 24-4 by switching the emission direction by a mirror. The exposure unit 25 also scans the laser beam in the axial direction of the photoconductor (the depth direction in FIG. 1) by a polygon mirror. This scanning of the laser beam is so-called main scanning, and the direction is called the main scanning direction.

[0017] The transfer roller 26 is disposed parallel to the support roller 23, and sandwiches the belt 20 between the support roller 23 and the transfer roller 26. The transfer roller 26 sandwiches the print paper sent out from the registration roller 14 between the transfer roller 26 and the image carrying surface of the belt 20. The transfer roller 26 then transfers the developer image formed on the image carrying surface of the belt 20 to the print paper by electrostatic force. In other words, the support roller 23 and the transfer roller 26 form a transfer section. There are cases where the developer is not completely transferred to the print paper and remains on the image carrying surface of the belt 20. For this reason, the developer adhering to the image carrying surface of the belt 20 after passing between the support roller 23 and the transfer roller 26 is removed by a cleaner (not shown) before it reaches the image forming unit 24-4. Thus, the print engine 2 forms an image on the print paper fed by the registration rollers 14 by electrophotography.

[0018] The fixing unit 3 fixes the developer onto the print paper sent out from the print engine 2 by melting and pressing the developer onto the print paper. The fixing unit 3 includes a fixing belt 30, a pressure pad 31, a heater 32, a press roller 33, a peeling plate 34, and a temperature sensor 35. Note that the fixing belt 30 and the press roller 33 are shown in cross section on a plane perpendicular to the rotation axis.

[0019] The fixing belt 30 is an endless belt made of, for example, a heat-resistant resin. The fixing belt 30 is supported by a support mechanism (not shown) so as to rotate around a rotation axis extending in the depth direction in FIG. 1. The length of the fixing belt 30 in the rotation axis direction is greater than the maximum length (hereinafter referred to as width) of a print paper in a direction (depth direction in FIG. 1) perpendicular to the print paper transport direction (up-down direction in FIG. 1). The outer diameter of the fixing belt 30 is typically smaller than the length in the rotation axis direction. Therefore, the rotation axis direction is the longitudinal direction of the fixing belt 30. The fixing belt 30 is heated by the heater 32 to heat the print paper and the developer attached to the print paper. The pressure pad 31 is provided so as to be in contact with the inner surface of the fixing belt 30 , and presses the fixing belt 30 against the press roller 33 .

[0020] The heater 32 heats the fixing belt 30. The heater 32 is, for example, an IH (induction heating) heater, but any other type of heater can be used as appropriate. The heater 32 may have only one heat generating element, or may have multiple heat generating elements arranged in the direction of the rotation axis. Thus, the heater 32 generates heat to heat the print paper via the fixing belt 30, and is an example of a heat generating section.

[0021] The press roller 33 is provided in parallel with the fixing belt 30. The press roller 33 is supported by a support mechanism (not shown) so as to rotate around a rotation axis extending in the depth direction in FIG. 1. The length of the press roller 33 in the rotation axis direction is larger than the maximum width of the print paper. The outer diameter of the press roller 33 is typically smaller than the length in the rotation axis direction. Therefore, the rotation axis direction is the longitudinal direction of the press roller 33. The press roller 33 sandwiches the print paper sent out from the print engine 2 between itself and the fixing belt 30, and sends it out together with the fixing belt 30 to the ADU 4. Thus, the press roller 33 presses the print paper when sandwiching the print paper together with the fixing belt 30 between itself and the pressing pad 31. In other words, the fixing belt 30, the pressing pad 31, and the press roller 33 work together to function as a pressing unit. The press roller 33 is also heated by the heat of the fixing belt 30, and plays a part in the function of heating the developer attached to the print paper. However, the function as the fixing unit is not limited to the above configuration, and any structure may be used as long as it can press the print paper. For example, instead of the fixing belt 30 and the pressure pad 31, a general roller may be used, and at least one of the roller and the press roller 33 may be pressed toward the other roller to realize the function as the pressing unit. Alternatively, instead of the press roller 33, a structure similar to the fixing belt 30 and the pressure pad 31 may be provided to realize the function as the pressing unit. Furthermore, for example, the function as the pressing unit may be realized by a structure in which the print paper passes between a roller and a fixed plate that are in contact with each other, and the roller and the fixed plate may realize the function as the pressing unit. The printing paper can also be heated in various other ways as appropriate, instead of the way in which the fixing belt 30 and the press roller 33 are heated. For example, instead of the heater 32, or in addition to the heater 32, a heater may be provided so as to directly heat the press roller 33. Alternatively, instead of the heater 32, or in addition to the heater 32, a heater may be provided so as to directly heat the printing paper before it is sandwiched between the fixing belt 30 and the press roller 33. In these cases, the heater provided instead of the heater 32, or in addition to the heater 32, also corresponds to a heat generating section.

[0022] The peeling plate 34 peels off the printing paper that has passed between the fixing belt 30 and the press roller 33 from the fixing belt 30 , and prevents the printing paper from being wound up in the fixing belt 30 . The temperature sensor 35 measures the temperature of the fixing belt 30. The temperature sensor 35 is typically disposed so as to measure the temperature of the fixing belt 30 near the center in the longitudinal direction. The temperature sensor 35 is an example of a detection unit. However, the temperature sensor 35 may be disposed in any manner as long as it can measure the temperature of the fixing belt 30. The temperature sensor 35 may be disposed so as to measure the temperature of the heater 32, the temperature of the press roller 33, or the temperature around the fixing belt or the press roller 33. That is, the detection unit may be realized so as to directly detect the temperature of the pressing unit, or indirectly detect the temperature.

[0023] The ADU 4 includes multiple rollers and selectively performs the following two operations. In the first operation, the print paper that has passed through the fixing unit 3 is sent directly toward the paper output tray 5. This first operation is performed when single-sided or double-sided printing is completed. In the second operation, the print paper that has passed through the fixing unit 3 is conveyed toward the paper output tray 5 side once, and then switched back and sent to the print engine 2. This second operation is performed when image formation on only one side of double-sided printing is completed. The paper discharge tray 5 receives the print paper on which an image has been formed and discharged.

[0024] Fig. 2 is a block diagram showing a schematic configuration relating to control of MFP 100. In Fig. 2, the same elements as those shown in Fig. 1 are given the same reference numerals, and detailed description thereof will be omitted. In addition to the scanner 101 and printer 102 , the MFP 100 includes a communication unit 103 , a system controller 104 , and an operation panel 105 .

[0025] A communication unit 103 performs processing for communicating with information terminals such as computers and image terminals such as facsimile machines via communication networks such as a LAN (local area network) and a public communication network. System controller 104 comprehensively controls each component of MFP 100 in order to realize the intended operation of MFP 100. Note that the intended operation of MFP 100 is, for example, an operation for realizing various functions realized by an existing MFP. The operation panel 105 includes an input device and a display device. An operator inputs instructions to the operation panel 105 using the input device. The operation panel 105 displays various information to be notified to the operator using the display device. For example, a touch panel can be used as the operation panel 105.

[0026] The above-mentioned fixing unit 3, ADU 4, image forming units 24-1 to 24-4, exposure unit 25, and transfer roller 26 provided in printer 102 are elements to be controlled. In addition to these, printer 102 also includes a motor group 6 as an element to be controlled. Motor group 6 includes a plurality of motors for rotating at least one of pickup rollers 11-1, 11-2, and 11-3, transport rollers 12-1, 12-2, and 12-3, transport roller 13, registration roller 14, support roller 21, transfer roller 26, fixing belt 30, and press roller 33, as well as rollers included in ADU 4.

[0027] Printer 102 further includes a sensor group 7 , a printer controller 81 , a formation controller 82 , an exposure controller 83 , a transfer controller 84 , a fusing controller 85 , an inversion controller 86 , and a motor controller 87 . The sensor group 7 includes various sensors for monitoring the operating state of the device. The printer controller 81 , under the control of the system controller 104 , comprehensively controls each component of the printer 102 in order to realize the desired operation of the printer 102 .

[0028] The formation controller 82, the exposure controller 83, the transfer controller 84, the fixing controller 85, the reversal controller 86, and the motor controller 87 all operate under the control of the printer controller 81, and control the operations of the image forming units 24-1 to 24-4, the exposure unit 25, the transfer roller 26, the ADU 4, and the motor group 6, respectively. The fixing controller 85 has a function of controlling the heat generation of the heater 32 so that the temperature measured by the temperature sensor 35 approaches the control temperature by adjusting the driving power supplied to the heater 32, for example. However, the fixing controller 85 controls the entire heater 32 collectively. In other words, the fixing controller 85 does not have a function of controlling the temperature of the heater 32 individually in each of the multiple regions in the longitudinal direction of the fixing belt 30. In other words, the fixing controller 85 has a function as a control unit.

[0029] FIG. 3 is a block diagram showing the main circuit configuration of the system controller 104. As shown in FIG. The system controller 104 includes a processor 1041 , a main memory 1042 , an auxiliary storage unit 1043 , an interface unit 1044 , and a transmission path 1045 .

[0030] The processor 1041, main memory 1042, and auxiliary storage unit 1043 are connected via a transmission line 1045 to constitute a computer that performs information processing for the above control. The processor 1041 corresponds to the central part of the computer. The processor 1041 executes information processing (to be described later) in accordance with information processing programs such as an operating system, middleware, and application programs.

[0031] The main memory 1042 corresponds to the main storage portion of the computer. The main memory 1042 includes a nonvolatile memory area and a volatile memory area. The main memory 1042 stores an information processing program in the nonvolatile memory area. The main memory 1042 may also store data required for the processor 1041 to execute processes for controlling each unit in the nonvolatile or volatile memory area. The main memory 1042 uses the volatile memory area as a work area where data is appropriately rewritten by the processor 1041.

[0032] The auxiliary storage unit 1043 corresponds to the auxiliary storage portion of the computer. As the auxiliary storage unit 1043, for example, well-known storage devices such as an EEPROM (electric erasable programmable read-only memory), a HDD (hard disk drive), and an SSD (solid state drive) can be used alone or in combination. The auxiliary storage unit 1043 stores data used by the processor 1041 when performing various processes and data generated by the processes in the processor 1041. The auxiliary storage unit 1043 stores an information processing program.

[0033] The interface unit 1044 performs well-known processing for transmitting and receiving data between the scanner 101, the printer 102, the communication unit 103, the system controller 104, and the operation panel 105. As the interface unit 1044, well-known interface devices or communication devices can be used alone or in combination. The transmission path 1045 includes an address bus, a data bus, and control signal lines, and transmits data and control signals between the connected components.

[0034] Next, a description will be given of the operation of MFP 100 configured as above. Note that, in the following, the description will focus on operations that are different from the operations of other existing MFPs, and descriptions of other operations will be omitted.

[0035] When a request is made to start a job such as copying that involves printing on the printer 102, the processor 1041 in the system controller 104 executes information processing for controlling the printer 102 (hereinafter referred to as print control processing) in accordance with an application program. In the following, the job requested here is referred to as the target job.

[0036] FIG. 4 is a flowchart of the print control process by the processor 1041. As ACT1, the processor 1041 takes in print data. For example, if the target job is copying, the processor 1041 makes the scanner 101 read the document and takes in the print data generated thereby from the scanner 101. Also, for example, if the target job is network printing or facsimile reception, the processor 1041 makes the communication unit 103 receive the print data. The processor 1041 acquires all print data to be printed for the target job.

[0037] In ACT2, the processor 1041 determines the print paper to be used. For example, when automatic paper selection is specified, the processor 1041 determines the size of the document represented by the print data acquired in ACT1, and sets the print paper suitable for printing a document of that size as the print paper to be used. For example, when an operation to specify the print paper to be used is performed by the operator on the operation panel 105, the processor 1041 sets the specified print paper as the print paper to be used.

[0038] As ACT3, the processor 1041 checks whether the print paper to be used is a print paper that has been determined in advance as a narrow paper. The size of the print paper to be the narrow paper may be determined arbitrarily by, for example, the designer of the MFP 100. However, the narrow paper is a print paper in which there is a large temperature difference between the area where the print paper contacts the press roller 33 (hereinafter referred to as the contact area) and the area where the print paper does not contact (hereinafter referred to as the non-contact area) in the longitudinal direction of the press roller 33, and which causes poor fixing due to the difference in the outer diameter of the press roller 33.

[0039] Here, the fixing failure caused by the difference in the outer diameter of the press roller 33 will be described. Fig. 5 is a diagram showing the results of measuring the temperature of the fixing belt 30 at multiple positions in the longitudinal direction of the fixing belt 30. Fig. 6 is a diagram showing the results of measuring the temperature of the press roller 33 at multiple positions in the longitudinal direction of the press roller 33. Note that Figs. 5 and 6 show the results of temperature measurement during printing of the same job.

[0040] 5 and 6, the dashed curves represent the measurement results when the leading edge of the first sheet of print paper passes between the fixing belt 30 and the press roller 33. In addition, in both Figs. 5 and 6, the solid curves represent the measurement results when the leading edge of the 50th sheet of print paper passes between the fixing belt 30 and the press roller 33. The width of the print paper used was approximately half the longitudinal length of the fixing belt 30 and the press roller 33. The print speed and controlled temperature were both preset as standard values ​​(hereinafter referred to as standard speed) and temperature (hereinafter referred to as standard temperature).

[0041] 5 and 6, as the number of consecutive prints increases, the temperatures at the center of both the fixing belt 30 and the press roller 33 decrease. This is because the heat is absorbed by the print paper when the print paper comes into contact with them. The press roller 33 changes its outer diameter due to thermal expansion, so that the central portion in the longitudinal direction has a smaller outer diameter than the ends in the longitudinal direction. This leads to a decrease in the pressing force of the press roller 33 on the fixing belt 30 at the central portion, which may cause fixing failure at the central portion of the press roller 33.

[0042] For the reasons described above, such fixing failures are more likely to occur as the width of the print paper becomes narrower. Therefore, for example, the designer of the MFP 100 may determine, based on experiments, simulations, or empirical rules, that print paper sizes that cause fixing failures to be a problem are narrow-width paper. As an example, it is assumed that A5 size and ST-R size print paper, which are 150 mm or less in width, are defined as narrow-width paper.

[0043] If the print paper used corresponds to narrow paper, the processor 1041 judges YES in ACT3 in FIG. 4 and proceeds to ACT4. In ACT4, the processor 1041 determines the total number of prints for the target job. For example, the processor 1041 checks the number of pages of the document represented by the print data captured in ACT1, and determines the total number of prints by multiplying the number of pages by the number of prints included in the print data or the number of prints separately specified.

[0044] In ACT5, processor 1041 checks whether the total number of prints determined in ACT4 corresponds to a predetermined large quantity of prints. For example, processor 1041 determines that a print corresponds to a large quantity of prints when the number of prints exceeds a predetermined threshold value that takes into consideration the relationship between the number of prints and the occurrence of transfer failures. Note that the type of situation that is determined to correspond to a large quantity of prints or the specific process by which this determination is made may be appropriately determined by the designer of MFP 100, for example, based on experiments, simulations, or empirical rules. For example, the above threshold value may be changed depending on the size of the print paper used.

[0045] If the printing does not correspond to large volume printing, the processor 1041 judges NO in ACT 5 and proceeds to ACT 6. If the printing paper to be used is not narrow paper, the processor 1041 judges NO in ACT 3 and proceeds to ACT 6. In other words, the processor 1041 proceeds to ACT 6 in both cases when the printing paper to be used is not narrow paper or when the printing does not correspond to large volume printing.

[0046] As ACT6, the processor 1041 instructs the printer controller 81 to start printing based on the print data captured in ACT1. In response to such an instruction from the system controller 104, the printer controller 81 operates each unit to print the document represented by the print data on the print paper. This operation may be the same as that performed by another printer of the same type, for example. However, the printer controller 81 instructs the fixing controller 85 to set the control temperature in the fixing unit 3 to the standard temperature. The printer controller 81 also instructs the formation controller 82, the exposure controller 83, the reversal controller 86, and the motor controller 87 to set the print speed to a predetermined standard speed. The standard temperature is typically set separately for monochrome printing and color printing, and the standard temperature for color printing is higher than the standard temperature for monochrome printing. Also, different standard temperatures may be set for each case, such as when performing deceleration printing or when the print paper used is thick paper.

[0047] In ACT7, the processor 1041 waits for the completion of the printing instructed to start in ACT6. Then, if the processor 1041 is notified of the completion of the printing from the printer controller 81, the result is YES, and the print control process ends.

[0048] On the other hand, if the print paper used is narrow and corresponds to a large volume of printing, the processor 1041 judges YES in ACT5 and proceeds to ACT8. As ACT8, the processor 1041 instructs the printer controller 81 to change the settings related to the control temperature and the print speed. For example, the processor 1041 instructs the printer controller 81 to change the control temperature to an increased temperature set higher than the standard temperature. Also, the processor 1041 instructs the printer controller 81 to change the print speed to a reduced speed set lower than the standard speed. The increased temperature and the reduced speed may be appropriately determined by, for example, the designer of the MFP 100 based on experiments, simulations, or empirical rules. It is desirable that the increased temperature is a temperature at which the temperature difference in the longitudinal direction of the press roller 33 is reduced to a degree that does not cause fixing failure. It is desirable that the increased temperature is determined to a degree that does not cause deformation or the like in various elements that undergo temperature changes due to heat generation by the heater 32. It is desirable that the reduced speed is determined so that the reduction amount with respect to the standard speed is kept to a necessary minimum in order to minimize the decrease in productivity. It is desirable that the increased temperature is determined to a temperature higher than any of the multiple standard temperatures when the standard temperature is changed according to the printing conditions as described above. Thus, the processor 1041 executes information processing based on the information processing program, and the computer with the processor 1041 as the central part functions as a setting unit.

[0049] In ACT9, the processor 1041 instructs the printer controller 81 to start printing based on the print data captured in ACT1. In response to such an instruction from the system controller 104, the printer controller 81 operates each section to print the document represented by the print data on print paper. This operation may be similar to that performed by, for example, another printer of the same type. However, the printer controller 81 instructs the fixing controller 85 to increase the controlled temperature in the fixing unit 3. The printer controller 81 also instructs the formation controller 82, the exposure controller 83, the reversal controller 86, and the motor controller 87 to reduce the print speed.

[0050] In ACT10, the processor 1041 waits for the completion of the printing instructed to start in ACT 9. If the processor 1041 is notified of the completion of the printing from the printer controller 81, the result of the determination is YES, and the process proceeds to ACT11. In ACT11, the processor 1041 instructs the printer controller 81 to return the settings changed in ACT8 to their original values. The processor 1041 instructs the printer controller 81 to return the control temperature and print speed to the standard temperature and standard speed, for example. Then, the processor 1041 ends the print control process. As described above, in the MFP 100, in a large volume of continuous printing using narrow print paper, the control temperature is set to an increased temperature and the print speed is set to a reduced speed.

[0051] Fig. 7 is a diagram showing the results of measuring the temperature of the fixing belt 30 at a plurality of positions in the longitudinal direction of the fixing belt 30. Fig. 8 is a diagram showing the results of measuring the temperature of the press roller 33 at a plurality of positions in the longitudinal direction of the press roller 33. Figs. 7 and 8 show the results of temperature measurement during printing of the same job. 7 and 8 are measured under the same conditions as those in FIGS. 5 and 6, except that the control temperature and print speed are changed to increasing temperature and decreasing speed.

[0052] The maximum temperature difference of the press roller 33 on the 50th sheet is ΔTB in Fig. 8, which is smaller than ΔTA in Fig. 6. Therefore, the outer diameter difference according to the longitudinal position of the press roller 33 is suppressed to be smaller than when the controlled temperature and print speed are kept at the standard temperature and standard speed.

[0053] FIG. 9 is a diagram showing the relationship between the control temperature and the print speed and the temperature difference according to the position in the longitudinal direction of the press roller 33. In FIG. 9, it can be seen that the temperature difference tends to become smaller as the control temperature increases and as the print speed decreases, and as a result, the temperature difference ΔTB is smaller than the temperature difference ΔTA, as described above.

[0054] FIG. 10 is a diagram showing the relationship between the temperature difference and the outer diameter difference according to the position in the longitudinal direction of the press roller 33. 10, it can be seen that the smaller the temperature difference, the smaller the outer diameter difference tends to be. Therefore, by reducing the temperature difference ΔTA as described above, the outer diameter difference according to the position in the longitudinal direction of the press roller 33 is kept small. Thus, according to the MFP 100, the variation in pressing force depending on the position in the longitudinal direction of the press roller 33 is reduced, and the possibility of poor fixing can be reduced.

[0055] Furthermore, the MFP 100 does not reduce the print speed if the print paper used is not narrow paper or if the job is not a large volume print. Therefore, the print speed reduction is limited to some jobs, and the decrease in productivity is kept small.

[0056] Furthermore, when the control temperature and print speed are set to the increased temperature and reduced speed before printing of one job starts, the MFP 100 maintains the control temperature and print speed at the increased temperature and reduced speed until printing of the job ends, thereby reducing the possibility of poor fixing occurring in all printing of the job.

[0057] FIG. 11 is a diagram showing the relationship between the control temperature, the print speed and the offset level. From Fig. 11, it can be seen that the offset level tends to be reduced by increasing the control temperature and by reducing the print speed. The offset level is a visual evaluation of the effect on image quality of residual images caused by developer that has adhered from the print paper to the fixing belt 30 and is redeposited on the print paper. If the offset level is below OAA, for example, and the residual images are kept within an acceptable level, it is effective to set the print speed to 50 CPM or less.

[0058] This embodiment can be modified in various ways as follows. 4, the processor 1041 may instruct the printer controller 81 to change only the settings related to the control temperature. In other words, the print speed may remain at the standard speed.

[0059] After issuing an instruction to start printing in ACT9, the processor 1041 may change at least one of the control temperature and the print speed for some reason before confirming the completion of printing in ACT10.

[0060] The print control process may be executed by a processor provided in the printer controller 81 .

[0061] The fixing unit 3 may be modified in any manner so long as it has the function of heating and pressing the paper, for example, by using a roller instead of the fixing belt 30, or by using a belt instead of the press roller 33.

[0062] Each function realized by the processor 1041 through information processing can be realized in part or in whole by hardware that executes information processing not based on a program, such as a logic circuit, etc. Also, each of the above functions can be realized by combining the above hardware, such as the logic circuit, with software control.

[0063] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. The invention as originally claimed in the present application is set forth below. [Note 1] A heat generating unit that generates heat to heat the paper conveyed in a conveying direction over the entire area in a direction perpendicular to the conveying direction; a pressing unit that applies pressure to the paper heated by the heat generating unit over an entire area in a direction perpendicular to the conveying direction; A detection unit that detects the temperature of the pressing unit; a control unit that controls the heat generating unit so as to bring the temperature detected by the detection unit closer to a control temperature; a setting unit that sets one of a plurality of different candidate temperatures as the control temperature based on the number of sheets to be imaged and a paper size to be used in one job before starting image formation for the job; An image forming apparatus comprising: [Additional Note 2] The setting unit further sets an image formation speed according to the candidate temperature to be set as the control temperature. 2. The image forming apparatus according to claim 1. [Additional Note 3] The setting unit maintains the setting before the start of image formation for one job until the end of the one job. 3. The image forming apparatus according to claim 1 or 2. [Note 4] The setting unit can determine that the job is in a predetermined large volume printing state based on a total number of sheets of image formation, and for a job using paper of a paper size whose width in a direction perpendicular to the transport direction is smaller than a specified width, sets the control temperature to a higher candidate temperature than for other cases. The image forming apparatus according to any one of claims 1 to 3. [Additional Note 5] When the number of sheets on which images are formed in one job is greater than a specified number and the width of the sheet size in the direction perpendicular to the conveying direction is smaller than the specified width, the setting unit sets a target speed that is lower than the target speed in other cases. 5. The image forming apparatus according to claim 4. [Appendix 6] The pressing unit includes a belt that sandwiches the paper between itself and another member, The detection unit detects the temperature of the belt. The image forming apparatus according to any one of claims 1 to 5. [Explanation of symbols]

[0064] 1...paper feed unit, 2...print engine, 3...fixing unit, 4...ADU, 5...paper output tray, 6...motor group, 7...sensor group, 10-1 to 10-3...paper feed cassette, 11-1 to 11-3...pickup roller, 12-1 to 12-3...conveyor roller, 13...conveyor roller, 14...registration roller, 20...belt, 21 to 23...support roller, 24-1 to 24-4...image forming unit, 25...exposure unit, 26...transfer roller, 30...fixing belt, 31...pressure pad, 32...heater, 33...press roller, 34... Peeling plate, 35...temperature sensor, 81...printer controller, 82...formation controller, 83...exposure controller, 84...transfer controller, 85...fixing controller, 86...reversal controller, 87...motor controller, 101...scanner, 102...printer, 103...communication unit, 104...system controller, 105...operation panel, 1041...processor, 1042...main memory, 1043...auxiliary memory unit, 1044...interface unit, 1045...transmission path.

Claims

1. a heat generating section that generates heat to heat the paper being transported in a transport direction over an entire area in a direction perpendicular to the transport direction; a pressing unit that applies pressure to the paper heated by the heat generating unit over an entire area in a direction perpendicular to the conveying direction; A detection unit that detects the temperature of the pressing unit; a control unit that controls the heat generating unit so that the temperature detected by the detection unit approaches a control temperature; a setting unit which, before starting image formation for one job, sets a predetermined standard temperature as the control temperature when either one of the following two conditions is not met: (1) the number of sheets on which images are formed in the job is a number predetermined as a large volume print, and (2) the paper used is a paper predetermined as a narrow paper, and sets a predetermined increased temperature higher than the standard temperature as the control temperature when both of the two conditions are met; An image forming apparatus comprising:

2. The setting unit further sets a standard speed as an image forming speed when the standard temperature is set as the control temperature, and sets a reduced speed lower than the standard speed as the image forming speed when the increased temperature is set as the control temperature. The image forming apparatus according to claim 1 .

3. the setting unit maintains the setting before the start of image formation for one job until the end of the one job.

3. The image forming apparatus according to claim 1 or 2.

4. the setting unit defines a sheet of paper having a size whose width in a direction perpendicular to the transport direction is smaller than a specified width as the narrow-width sheet. The image forming apparatus according to any one of claims 1 to 3.

5. the setting unit determines that the number of sheets for which images have been formed exceeds a predetermined threshold value as being a large quantity of prints. The image forming apparatus according to claim 4 .

6. the pressing unit includes a belt that sandwiches the paper between itself and another member, The detection unit detects the temperature of the belt. The image forming apparatus according to any one of claims 1 to 5.

Images