Patent Description:
For example, in an electrophotographic image forming apparatus, a heated roller is used to fix a developer attached to the paper. If the pressure applied to the sheet and the developer is reduced by the roller, there is a possibility that a fixing failure occurs. In view of such circumstances, it has been desired to reduce the possibility of occurrence of a fixing failure. <CIT>, <CIT> and <CIT> disclose image forming apparatus. Specifically, <CIT> discloses a medium width detector provided to detect a width of the print medium and output a detected width; and a heat controller configured to change a control condition in accordance with the second detection temperature, a calorific value of the heater and the detected width, and to thereby control a temperature of the fixation unit.

Hereinafter, an embodiment will be described with reference to the drawings. The same reference symbols in the drawings will denote the same or similar portions. Note that a multi-function peripheral (MFP) will be exemplified as an image forming apparatus in the following embodiment. Contents of various operations and various processes to be described below are examples, and it is possible to change the order of some operations and processes, omit some operations and processes, or add other operations and processes as appropriate.

First, the configuration of the MFP according to this embodiment will be described. <FIG> is a diagram schematically showing a mechanical configuration of an MFP <NUM> according to the embodiment. As shown in <FIG>, the MFP <NUM> includes a scanner <NUM> and a printer <NUM>.

The scanner <NUM> reads an image of a document and generates image data corresponding to the document. The scanner <NUM> uses, for example, an image sensor such as a charge-coupled device (CCD) line sensor to generate image data corresponding to the reflected light image from the reading surface of the document. The scanner <NUM> scans a document placed on a document table by the image sensor that moves along the document. The scanner <NUM> further scans a document conveyed by an auto document feeder (ADF) by a fixed image sensor.

The printer <NUM> forms an image on a medium on which an image is to be formed by an electrophotographic method. The medium is typically a print sheet such as cut paper. In the following description, it is assumed that a print sheet is used as a medium. However, as the medium, a sheet material made of paper different from the cut paper may be used, or a sheet material made of a material such as a resin other than paper may be used. The printer <NUM> has a color printing function of printing a color image on a print sheet and a monochrome printing function of printing a monochrome image on a print sheet. The printer <NUM> forms a color image by superimposing element images using developers including, for example, three colors of yellow, magenta, and cyan or four colors of those three colors and black. Further, the printer <NUM> forms a monochrome image using, for example, a developer of black. The developer is, for example, a toner. The developer may include, for example, a toner and a carrier. However, the printer <NUM> may include only one of the color printing function and the monochrome printing function.

In the exemplary configuration shown in <FIG>, the printer <NUM> includes a paper feeding unit <NUM>, a print engine <NUM>, a fixing unit <NUM>, an automatic double-sided unit (ADU) <NUM>, and a paper receiving tray <NUM>. The paper feeding unit <NUM> includes paper feeding cassettes <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, pick-up rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, conveyance rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, conveyance rollers <NUM>, and resist rollers <NUM>.

The paper feeding cassettes <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> store print sheets in a stacked state. The print sheets stored in the paper feeding cassettes <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> may be of different types of print sheets having different sizes and materials or may be of the same type of print sheets. In addition, the paper feeding unit <NUM> may include a manual paper feed tray. The pick-up rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> take out print sheets one by one from the respective paper feeding cassettes <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>. The pick-up rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> feed the taken out print sheets to the respective conveyance rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>. The conveyance rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> feed the print sheets fed from the respective pick-up rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> to the conveyance rollers <NUM> via a conveyance path formed by a guide member (not shown).

The conveyance rollers <NUM> further convey the print sheets fed from any one of the conveyance rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> and feed the print sheets to the resist rollers <NUM>.

The resist rollers <NUM> correct the inclination of the print sheet. The resist rollers <NUM> adjust the timing at which the print sheet is fed to the print engine <NUM>. The paper feeding cassettes, the pick-up rollers, and the conveyance rollers are not limited to being in three sets, and any number of sets may be provided. Further, if a manual paper feed tray is provided, the paper feeding cassettes, and the pick-up rollers and conveyance rollers paired with the paper feeding cassettes need not be provided.

The print engine <NUM> includes a transfer belt <NUM>, support rollers <NUM>, <NUM>, and <NUM>, image forming units <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, an exposure unit <NUM>, and a transfer roller <NUM>. The transfer belt <NUM> is an endless belt and is supported by the support rollers <NUM>, <NUM>, and <NUM> so as to maintain the state shown in <FIG>. The transfer belt <NUM> rotates counterclockwise in <FIG> with the rotation of the support roller <NUM>. The transfer belt <NUM> temporarily carries an image of a developer to be formed on the print sheet on the outer surface (hereinafter, referred to as an image carrying surface). For example, semiconductive polyimide is used for the transfer belt <NUM> in terms of heat resistance and abrasion resistance. So-called sub-scanning is achieved by the movement of the image carrying surface with the rotation of the transfer belt <NUM>. The moving direction of the image carrying surface is also referred to as a sub-scanning direction.

The image forming units <NUM>-<NUM> to <NUM>-<NUM> each include a photoreceptor, a charger, a developing unit, a primary transfer roller, and a cleaner, and each have a well-known structure for performing image formation in an electrophotographic method in cooperation with the exposure unit <NUM>. The image forming units <NUM>-<NUM> to <NUM>-<NUM> are arranged along the transfer belt <NUM> in a state in which the axial directions of the respective photoreceptors are parallel to each other. The image forming units <NUM>-<NUM> to <NUM>-<NUM> are different from each other only in the colors of developers used and have the same structures and operations. The photoreceptors of the image forming units <NUM>-<NUM> to <NUM>-<NUM> are uniformly charged by the charger. After the charging, the photoreceptors of the image forming units <NUM>-<NUM> to <NUM>-<NUM> are exposed by the exposure unit <NUM>, and thus electrostatic latent images corresponding to the colors of the developers are formed. The image forming unit <NUM>-<NUM> develops an electrostatic latent image by the developing unit using, for example, a black developer and forms an element image (image of black developer) on the photoreceptor. The image forming unit <NUM>-<NUM> develops an electrostatic latent image by the developing unit using, for example, a cyan developer and forms an element image (image of cyan developer) on the photoreceptor. The image forming unit <NUM>-<NUM> develops an electrostatic latent image by the developing unit using, for example, a magenta developer and forms an element image (image of magenta developer) on the photoreceptor. The image forming unit <NUM>-<NUM> develops an electrostatic latent image by the developing unit using, for example, a yellow developer and forms an element image (image of yellow developer) on the photoreceptor. The image forming units <NUM>-<NUM> to <NUM>-<NUM> transfer the element images of the respective colors from the respective photoreceptors onto the image carrying surface of the transfer belt <NUM> by the primary transfer rollers so as to overlap each other. Thus, the image forming units <NUM>-<NUM> to <NUM>-<NUM> form a color image in which the element images of the respective colors are superimposed on the image carrying surface of the transfer belt <NUM> at the time at which the transfer belt <NUM> passes through the image forming unit <NUM>-<NUM>. Note that a developer container for storing the developers of the respective colors is disposed in a space above the transfer belt <NUM>, for example, though not shown in the figure.

The exposure unit <NUM> exposes the photoreceptors of the respective image forming units <NUM>-<NUM> to <NUM>-<NUM> in accordance with the image data representing the element images of the respective colors to form electrostatic latent images on the photoreceptors as described above. As the exposure unit <NUM>, a laser scanner, a light emitting diode (LED) head, or the like is used. If a laser scanner is used as the exposure unit <NUM>, the exposure unit <NUM> includes, for example, a semiconductor laser element, a polygon mirror, an imaging lens system, and a mirror. In this case, for example, the exposure unit <NUM> selectively causes a laser beam emitted from the semiconductor laser element in accordance with the image data to enter each of the photoreceptors of the image forming units <NUM>-<NUM> to <NUM>-<NUM> by switching the emission direction using the mirror. Further, the exposure unit <NUM> scans the laser beam in an axial direction (depth direction in <FIG>) of the photoreceptor using the polygon mirror. The scanning of the laser beam is so-called main scanning. Its direction is called a main scanning direction.

The transfer roller <NUM> (secondary transfer roller) is disposed in parallel with the support roller <NUM> and sandwiches the transfer belt <NUM> together with the support roller <NUM>. The transfer roller <NUM> sandwiches the print sheet fed from the resist rollers <NUM> together with the image carrying surface of the transfer belt <NUM>. The transfer roller <NUM> transfers the developer image formed on the image carrying surface of the transfer belt <NUM> to the print sheet using an electrostatic force. In other words, the support roller <NUM> and the transfer roller <NUM> constitute a transfer unit (transfer device). The developer may remain on the image carrying surface of the transfer belt <NUM> without being completely transferred to the print sheet. Therefore, the developer adhering to the image carrying surface of the transfer belt <NUM> after passing between the support roller <NUM> and the transfer roller <NUM> is removed by the cleaner (not shown) before reaching the image forming unit <NUM>-<NUM>. In such a manner, the print engine <NUM> forms an image (developer image) on the print sheet fed by the resist rollers <NUM> by the electrophotographic method.

The fixing unit <NUM> presses the developer adhering as an image of the developer to the print sheet fed from the print engine <NUM> while melting the developer, to fix the developer onto the print sheet. As shown in <FIG>, the fixing unit <NUM> includes a fixing belt <NUM>, a pressing pad <NUM>, a heater <NUM>, a press roller <NUM>, a separation plate <NUM>, and a temperature sensor <NUM>. Note that the fixing belt <NUM> and the press roller <NUM> are shown in cross sections on a plane perpendicular to the rotation axis.

The fixing belt <NUM> is, for example, an endless belt made of a heat-resistant resin. The fixing belt <NUM> is supported by a support mechanism (not shown) so as to rotate about a rotation axis extending in the depth direction in <FIG>. The length of the fixing belt <NUM> in the rotation axis direction is longer than the maximum value of the length (hereinafter, referred to as width) of the print sheet in a direction (depth direction in <FIG>) perpendicular to a print sheet conveyance direction (vertical direction in <FIG>). The outer diameter of the fixing belt <NUM> is typically smaller than the length in the rotation axis direction. Therefore, the rotation axis direction is the longitudinal direction of the fixing belt <NUM>. The fixing belt <NUM> is heated by the heater <NUM> to heat the print sheet and the developer adhering to the print sheet. The pressing pad <NUM> is provided so as to come into contact with the inner surface of the fixing belt <NUM>, and presses the fixing belt <NUM> to the press roller <NUM>.

The heater <NUM> generates heat to heat the fixing belt <NUM>. The heater <NUM> is, for example, an induction heating (IH) heater, but any other types of heater can be used as appropriate. The heater <NUM> may include only one heating element or may include a plurality of heating elements arranged side by side in the rotation axis direction. In such a manner, the heater <NUM> generates heat to heat the print sheet through the fixing belt <NUM>. The heater <NUM> is an exemplary heat generation unit.

The press roller <NUM> is provided in parallel to the fixing belt <NUM>. The press roller <NUM> is supported by a support mechanism (not shown) so as to rotate about the rotation axis extending in the depth direction in <FIG>. The length of the press roller <NUM> in the rotation axis direction is longer than the maximum width of the print sheet. The outer diameter of the press roller <NUM> is typically smaller than the length in the rotation axis direction. Therefore, the rotation axis direction is the longitudinal direction of the press roller <NUM>. The press roller <NUM> sends the print sheet fed from the print engine <NUM> to the ADU <NUM> together with the fixing belt <NUM> while sandwiching the print sheet between the press roller <NUM> and the fixing belt <NUM>. In such a manner, the press roller <NUM> presses the print sheet when the print sheet is sandwiched between the press roller <NUM> and the fixing belt <NUM> together with the pressing pad <NUM>. In other words, the cooperation of the fixing belt <NUM>, the pressing pad <NUM>, and the press roller <NUM> provides the function as a pressing member. Note that the press roller <NUM> is also heated by the heat of the fixing belt <NUM> and operates as part of the function of heating the developer adhering to the print sheet. Although the function of the fixing unit <NUM> as the pressing member is implemented by the above-mentioned configuration, the fixing unit <NUM> is not limited to the above-mentioned configuration and only needs to be capable of pressing the print sheet. For example, a common roller may be used instead of the fixing belt <NUM> and the pressing pad <NUM>, and the function as a pressing member may be implemented when at least one of such a roller or the press roller <NUM> is pressed in the direction of the other roller. Alternatively, for example, instead of the press roller <NUM>, the function as a pressing member may be implemented by providing a structure similar to the fixing belt <NUM> and the pressing pad <NUM>. Furthermore, for example, the function as a pressing member may be implemented by a roller and a fixing plate being in contact with each other when a structure in which the print sheet is caused to pass between the roller and the fixing plate is provided. Instead of heating the fixing belt <NUM> and the press roller <NUM>, other various forms can also be appropriately adopted in heating the print sheet. For example, the fixing unit <NUM> may include a heater that directly heats the press roller <NUM> instead of the heater <NUM> or in addition to the heater <NUM>. Alternatively, the fixing unit <NUM> may include a heater that directly heats the print sheet before the print sheet is sandwiched between the fixing belt <NUM> and the press roller <NUM>, for example, instead of the heater <NUM> or in addition to the heater <NUM>. In those cases, a heater provided instead of the heater <NUM> or in addition to the heater <NUM> also corresponds to the heat generation unit.

The separation plate <NUM> separates the print sheet passing between the fixing belt <NUM> and the press roller <NUM> from the fixing belt <NUM>, and prevents the print sheet from being caught in the fixing belt <NUM>. The temperature sensor <NUM> measures the temperature of the fixing belt <NUM>. The temperature sensor <NUM> is typically disposed to measure the temperature near the center of the fixing belt <NUM> in the longitudinal direction. The temperature sensor <NUM> is an example of a detection unit. However, the temperature sensor <NUM> may be provided in any manner if it can measure the temperature of the fixing belt <NUM>. The temperature sensor <NUM> may be provided so as to measure the temperature of the heater <NUM>, the temperature of the press roller <NUM>, or the temperature of the periphery of the fixing belt <NUM> or the press roller <NUM>. In other words, the detection unit may be achieved so as to directly detect the temperature of the pressing member or indirectly detect the temperature of the pressing member.

The ADU <NUM> includes a plurality of rollers and selectively performs the following two operations. In the first operation, the print sheet having passed through the fixing unit <NUM> is directly sent to the paper receiving tray <NUM>. The first operation is performed when single-sided printing or double-sided printing is completed. In the second operation, after the print sheet having passed through the fixing unit <NUM> is once conveyed to the paper receiving tray <NUM>, the print sheet is switched back and sent to the print engine <NUM>. The second operation is performed when printing (image formation) on only one side in the double-sided printing is completed. The paper receiving tray <NUM> receives the print sheet discharged after the image is formed thereon.

<FIG> is a block diagram schematically showing a configuration relating to the control of the MFP <NUM>. In <FIG>, the same elements as those shown in <FIG> will be denoted by the same reference numerals, and detailed description thereof will be omitted. In addition to the scanner <NUM> and the printer <NUM>, the MFP <NUM> includes a communication unit <NUM>, a system controller <NUM>, and an operation panel <NUM>.

The communication unit <NUM> performs processing for communicating with an information terminal such as a computer device and an image terminal such as a facsimile device through a communication network such as a local area network (LAN) or a public communication network. The system controller <NUM> integrally controls the units constituting the MFP <NUM> in order to achieve a desired operation to serve as the MFP <NUM>. Note that the desired operation to serve as the MFP <NUM> is, for example, an operation for achieving various functions implemented by conventional MFPs. The operation panel <NUM> includes an input device and a display device. The operation panel <NUM> inputs an instruction by an operator through the input device. The operation panel <NUM> displays various types of information to be notified to the operator by the display device. For example, a touch panel can be used as the operation panel <NUM>.

The above-mentioned fixing unit <NUM>, ADU <NUM>, image forming units <NUM>-<NUM> to <NUM>-<NUM>, exposure unit <NUM>, and transfer roller <NUM> of the printer <NUM> are elements to be controlled. In addition to those elements, the printer <NUM> includes a motor group <NUM> as an element to be controlled. The motor group <NUM> includes a plurality of motors for rotating at least one of the pick-up rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, the conveyance rollers <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, the conveyance rollers <NUM>, the resist rollers <NUM>, the support roller <NUM>, the transfer roller <NUM>, the fixing belt <NUM>, or the press roller <NUM>, and further a roller or the like included in the ADU <NUM>.

The printer <NUM> further includes a sensor group <NUM>, a printer controller <NUM>, a forming controller <NUM>, an exposure controller <NUM>, a transfer controller <NUM>, a fixing controller <NUM>, an inversion controller <NUM>, and a motor controller <NUM>. The sensor group <NUM> includes various sensors for monitoring the operating state of the apparatus. The printer controller <NUM> collectively controls the units constituting the printer <NUM> in order to achieve a desired operation to serve as the printer <NUM> under the control of the system controller <NUM>.

The forming controller <NUM>, the exposure controller <NUM>, the transfer controller <NUM>, the fixing controller <NUM>, the inversion controller <NUM>, and the motor controller <NUM> all operate under the control of the printer controller <NUM> to control the operations of the image forming units <NUM>-<NUM> to <NUM>-<NUM>, the exposure unit <NUM>, the transfer roller <NUM>, the ADU <NUM>, and the motor group <NUM>. Note that the fixing controller <NUM> has a function of controlling the heat generation of the heater <NUM> such that the temperature measured by the temperature sensor <NUM> approaches the fixing control temperature (hereinafter, simply referred to as control temperature) by adjusting the driving power supplied to the heater <NUM>, for example. However, the fixing controller <NUM> collectively controls the entire heater <NUM>. In other words, the fixing controller <NUM> does not have a function of controlling the temperature of the heater <NUM> individually in each of the plurality of regions of the fixing belt <NUM> in the longitudinal direction. In other words, the fixing controller <NUM> has a function as a control unit.

<FIG> is a block diagram showing a circuit configuration of a main part of the system controller <NUM>. The system controller <NUM> includes a processor <NUM>, a main memory <NUM>, an auxiliary storage device <NUM>, an interface unit <NUM>, and a transmission line <NUM>.

The processor <NUM>, the main memory <NUM>, and the auxiliary storage device <NUM> are connected to each other through the transmission line <NUM>, so that a computer that performs information processing for the control described above is configured. The processor <NUM> corresponds to the central portion of the computer. The processor <NUM> executes information processing to be described later in accordance with an operating system, middleware, and an information processing program such as an application program.

The main memory <NUM> corresponds to the main memory portion of the computer. The main memory <NUM> includes a non-volatile memory area and a volatile memory area. The main memory <NUM> stores an information processing program in the non-volatile memory area. The main memory <NUM> may also store, in the non-volatile or volatile memory area, data necessary for the processor <NUM> to perform processing for controlling each unit. The volatile memory area of the main memory <NUM> is used by the processor <NUM> as a work area in which data is appropriately rewritten.

The auxiliary storage device <NUM> corresponds to the auxiliary storage portion of the computer. As the auxiliary storage device <NUM>, for example, well-known storage devices such as an electric erasable programmable read-only memory (EEPROM), a hard disc drive (HDD), and a solid state drive (SSD) can be used alone or in combination. The auxiliary storage device <NUM> stores data used by the processor <NUM> to perform various types of processing and data generated by the processing of the processor <NUM>. The auxiliary storage device <NUM> stores, for example, data of a plurality of candidate temperatures of the control temperature. The data of the plurality of candidate temperatures is data of a predetermined temperature and includes, for example, data of an increased temperature (first candidate temperature) and a standard temperature (second candidate temperature) to be described later. Further, the auxiliary storage device <NUM> stores, for example, a plurality of candidate speeds of a print speed (image forming speed) to be described later. The data of the plurality of candidate speeds is data of a predetermined speed and includes, for example, data of a reduced speed (first candidate speed) and a standard speed (second candidate speed) to be described later. The auxiliary storage device <NUM> also stores an information processing program.

The interface unit <NUM> performs well-known processing for exchanging data between the scanner <NUM>, the printer <NUM>, the communication unit <NUM>, the system controller <NUM>, and the operation panel <NUM>. As the interface unit <NUM>, a well-known interface device, communication device, or the like can be used alone or in combination. The transmission line <NUM> includes an address bus, a data bus, a control signal line, and the like, and transmits data and control signals exchanged between the connected units.

Next, the operation of the MFP <NUM> configured as described above will be described. In the following description, an operation different from that of a well-known MFP will be mainly described, and description of other operations will be omitted.

The processor <NUM> of the system controller <NUM> executes information processing for controlling the printer <NUM> (hereinafter, referred to as print control processing) in accordance with an application program when the start of a job such as copying accompanied by printing (image forming) by the printer <NUM> is requested. In the following, the requested job will be referred to as a target job.

<FIG> is a flowchart of the print control processing by the processor <NUM>. In ACT1, the processor <NUM> captures print data. For example, if a target job (job accompanied by printing) is copying, the processor <NUM> causes the scanner <NUM> to read a document and captures the generated print data from the scanner <NUM>. For example, if the target job (job accompanied by printing) is network printing or facsimile reception, the processor <NUM> also causes the communication unit <NUM> to receive print data. Note that the processor <NUM> acquires all the print data to be printed in the target job.

In ACT2, the processor <NUM> determines print sheets to be used. For example, if the automatic selection of sheets is designated, the processor <NUM> determines the size of the document represented by the print data acquired in ACT1. The processor <NUM> sets the print sheets suitable to print the document of the determined size as the print sheets to be used. For example, if an operation of an operator who designates the print sheets to be used is received by the operation panel <NUM>, the processor <NUM> sets the designated print sheets as the print sheets to be used.

In ACT3, the processor <NUM> checks whether or not the print sheets to be used are print sheets defined as small-width sheets (specified sheets) in advance. Note that, for example, a designer or the like of the MFP <NUM> may arbitrarily determine which size of the print sheets is to be set as the small-width sheets. For example, the small-width sheets are print sheets having the width narrower than a predetermined width (specified width). However, the small-width sheet is a print sheet in which a temperature difference between a region in which the print sheet contacts (hereinafter, referred to as contact region) and a region in which the print sheet does not contact (hereinafter, referred to as non-contact region) with respect to the longitudinal direction of the press roller <NUM> (the rotation axis direction of the press roller <NUM>) is large, and a fixing failure occurs due to a difference in the outer diameter of the press roller <NUM>.

Here, description will be given on a fixing failure due to a difference in the outer diameter of the press roller <NUM>. <FIG> is a diagram showing the results obtained by measuring the temperature of the fixing belt <NUM> at a plurality of positions in the longitudinal direction of the fixing belt <NUM> (the rotation axis direction of the fixing belt <NUM>). The vertical axis of <FIG> represents the temperature of the fixing belt <NUM>. The horizontal axis of <FIG> represents the position in the longitudinal direction of the fixing belt <NUM>. The "front end" in the horizontal axis of <FIG> represents a position on one end side of the fixing belt <NUM> in the longitudinal direction, e.g., a position of the end on the near side of <FIG>. Further, the "center" in the horizontal axis of <FIG> represents a position of the center portion of the fixing belt <NUM> in the longitudinal direction. Further, the "rear end" in the horizontal axis of <FIG> represents a position on the other end side of the fixing belt <NUM> in the longitudinal direction, e.g., a position of the end on the depth side in <FIG>. <FIG> is a diagram showing the results obtained by measuring the temperature of the press roller <NUM> at a plurality of positions in the longitudinal direction of the press roller <NUM> (the rotation axis direction of the press roller <NUM>). The vertical axis of <FIG> represents the temperature of the press roller <NUM>. The horizontal axis of <FIG> represents the position in the longitudinal direction of the press roller <NUM>. The "front end" in the horizontal axis of <FIG> represents a position on one end side of the press roller <NUM> in the longitudinal direction, e.g., a position of the end on the near side of <FIG>. Further, the "center" in the horizontal axis of <FIG> represents a position of the center portion of the press roller <NUM> in the longitudinal direction. Further, the "rear end" in the horizontal axis of <FIG> represents a position on the other end side of the press roller <NUM> in the longitudinal direction, e.g., a position of the end on the depth side in <FIG>. Further, "ΔTA" in <FIG> represents the maximum temperature difference of the press roller <NUM>. Note that <FIG> show the results of the temperature measurement at the time of printing in the same job.

In both of <FIG>, the curved line of the broken line represents measured results obtained when the front end of the first print sheet passes between the fixing belt <NUM> and the press roller <NUM>. Further, in both of <FIG>, the curved line of the solid line represents measured results obtained when the front end of the 50th print sheet passes between the fixing belt <NUM> and the press roller <NUM>. The width of the print sheet used is approximately <NUM>/<NUM> the length of the fixing belt <NUM> and the press roller <NUM> in the longitudinal direction. The print speed (image forming speed) and the control temperature are a predetermined speed (hereinafter, referred to as standard speed) and a temperature (hereinafter, referred to as standard temperature) as standard values.

As can be seen from <FIG>, as the number of successive print sheets increases, the temperature at the center portions of both the fixing belt <NUM> and the press roller <NUM> decreases. This is because the fixing belt <NUM> and the press roller <NUM> are deprived of heat by the print sheets due to the contact of the print sheets. The number of successive print sheets means the number of sheets used for printing in succession. The outer diameter of the press roller <NUM> changes due to thermal expansion, and thus the outer diameter of the center portion in the longitudinal direction is smaller than that of the end in the longitudinal direction. This leads to a decrease in the pressing force against the fixing belt <NUM> at the center portion of the press roller <NUM>, which may cause a fixing failure at the center portion of the press roller <NUM>.

Such a fixing failure is apt to occur as the width of the print sheet becomes narrower because of the above-mentioned cause. In this regard, for example, the designer of the MFP <NUM> sets a print sheet of a size in which a fixing failure is problematic as a small-width sheet on the basis of experiments, simulations, empirical rules, and the like. For example, it is assumed that A5-size and ST-R-size print sheets having a width of <NUM> or less are defined as small-width sheets.

In ACT3 of <FIG>, if it is determined that the print sheet to be used is a small-width sheet (specified sheet) (YES in ACT3 of <FIG>), the processing of the processor <NUM> proceeds to ACT4. In other words, for example, if the width of the sheet to be used is narrower than a predetermined specified width, the processing of the processor <NUM> proceeds to ACT4. In ACT4, the processor <NUM> determines the total number of print sheets of the target job. The total number of print sheets means the total number of print sheets to be used for printing in the target job. For example, the processor <NUM> checks the number of pages of the document represented by the print data acquired in ACT1, and determines the total number of print sheets by multiplying the number of copies included in the print data or the number of separately designated copies by the number of pages.

In ACT5, the processor <NUM> checks whether or not the target job of the determined total number of print sheets (see ACT4) corresponds to a large-volume print job in which the number of print sheets is larger than a predetermined number of print sheets (a specified number of print sheets). The processor <NUM> determines that the target job corresponds to a large-volume print job when the determined total number of print sheets exceeds a predetermined threshold value. The threshold value is, for example, a predetermined value in consideration of the relationship between the number of print sheets and the occurrence of a fixing failure. Note that what kind of situation is determined to correspond to a large-volume print job, or what kind of processing is specifically used for the determination may be appropriately determined by, for example, a designer of the MFP <NUM> on the basis of experiments, simulations, empirical rules, and the like. For example, the threshold value may be changed in accordance with the size of the print sheet to be used.

In ACT5 described above, if it is determined that the target job of the determined total number of print sheets does not correspond to a large-scale print job (NO in ACT5), the processing of the processor <NUM> proceeds to ACT6. Further, in ACT3 described above, if it is determined that the print sheet to be used is not a small-width sheet (specified sheet) (NO in ACT3), the processing of the processor <NUM> proceeds to ACT6. In other words, if the print sheet to be used is not a small-width sheet and if the target job does not correspond to a large-volume print job, the processing of the processor <NUM> proceeds to ACT6.

In ACT6, the processor <NUM> instructs the printer controller <NUM> to start printing of the target job on the basis of the captured print data (see ACT1). In response to such an instruction from the system controller <NUM>, the printer controller <NUM> operates each unit to print the document represented by the print data on the print sheet. This operation may be similar to that performed by a well-known printer. However, the printer controller <NUM> instructs the fixing controller <NUM> to set the control temperature in the fixing unit <NUM> to the standard temperature. Further, the printer controller <NUM> instructs the forming controller <NUM>, the exposure controller <NUM>, the inversion controller <NUM>, and the motor controller <NUM> to set the print speed to a predetermined standard speed. Note that the standard temperature is typically determined separately at the time of monochrome printing and at the time of color printing. The standard temperature at the time of color printing is higher than that at the time of monochrome printing. In addition, different standard temperatures may be determined for the case of performing deceleration printing, the case where the print sheet to be used is thick paper, or the like.

In ACT7, the processor <NUM> waits for completion of printing of the target job, which has been instructed to start (see ACT6), by determining whether or not the completion of printing has been notified from the printer controller <NUM>. If it is determined that the completion of printing has been notified from the printer controller <NUM> (YES in ACT7), the processor <NUM> terminates the print control processing shown in <FIG>.

On the other hand, if it is determined in ACT3 that the print sheet to be used is a small-width sheet (specified sheet) (YES in ACT3) and it is determined in ACT5 that the target job corresponds to a large-volume print job (YES in ACT5), the processing of the processor <NUM> proceeds to ACT8. In other words, for example, if the width of the sheet to be used in the direction perpendicular to the conveyance direction is narrower than the specified width and if the total number of print sheets is larger than the specified number, the processing of the processor <NUM> proceeds to ACT8. In ACT8, the processor <NUM> instructs the printer controller <NUM> to change the settings of the control temperature and the print speed. For example, the processor <NUM> instructs the printer controller <NUM> to change the control temperature to an increased temperature (first candidate temperature) that is determined to be higher than the standard temperature (second candidate temperature). The processor <NUM> also instructs the printer controller <NUM> to change the print speed to a reduced speed determined to be lower than the standard speed (second candidate speed). The increased temperature and the reduced speed may be appropriately determined by, for example, the designer of the MFP <NUM> on the basis of experiments, simulations, empirical rules, and the like. Note that it is desirable that the increased temperature be a temperature reduced to the extent that the temperature difference of the press roller <NUM> in the longitudinal direction does not cause a fixing failure. Further, it is desirable that the increased temperature be determined to the extent that deformation or the like does not occur in various elements that cause a temperature change due to heat generation of the heater <NUM>. It is also desirable that the reduced speed be determined such that the amount of reduction relative to the standard speed is kept to a necessary minimum in order to minimize the decrease in productivity. Note that, for example, as described above, if the standard temperature is changed in accordance with a printing condition, the increased temperature is set to a temperature higher than any of the plurality of standard temperatures. Thus, when the processor <NUM> executes information processing based on the information processing program, the computer including the processor <NUM> as the central portion functions as the setting unit.

In ACT9, the processor <NUM> instructs the printer controller <NUM> to start printing of the target job on the basis of the captured print data (see ACT1). In response to such an instruction from the system controller <NUM>, the printer controller <NUM> operates each unit to print the document represented by the print data on the print sheet. This operation may be similar to the operation performed by a well-known printer, for example. However, the printer controller <NUM> instructs the fixing controller <NUM> to set the control temperature in the fixing unit <NUM> to the increased temperature (first candidate temperature). The printer controller <NUM> also instructs the forming controller <NUM>, the exposure controller <NUM>, the inversion controller <NUM>, and the motor controller <NUM> to set the print speed to the reduced speed (first candidate speed).

In ACT10, the processor <NUM> waits for completion of printing, which has been instructed to start (see ACT9), by determining whether or not the completion of printing of the target job has been notified from the printer controller <NUM>. If it is determined that the completion of printing of the target job has been notified from the printer controller <NUM> (YES in ACT10), the processing of the processor <NUM> proceeds to ACT11. In ACT11, the processor <NUM> instructs the printer controller <NUM> to restore the changed settings (see ACT8). The processor <NUM> instructs the printer controller <NUM> to restore, for example, the control temperature and the print speed to the standard temperature and the standard speed. The processor <NUM> then terminates the print control processing shown in <FIG>. As described above, in the MFP <NUM>, in a large-volume successive printing using narrow print sheets, the control temperature is set to the increased temperature (first candidate temperature), and the print speed is set to the reduced speed (first candidate speed).

<FIG> is a diagram showing the results obtained by measuring the temperature of the fixing belt <NUM> at a plurality of positions in the longitudinal direction of the fixing belt <NUM>. The vertical axis of <FIG> represents the temperature of the fixing belt <NUM>. The horizontal axis of <FIG> represents the position in the longitudinal direction of the fixing belt <NUM>. The "front end" in the horizontal axis of <FIG> represents a position on one end side of the fixing belt <NUM> in the longitudinal direction, e.g., a position of the end on the near side of <FIG>. Further, the "center" in the horizontal axis of <FIG> represents a position of the center portion of the fixing belt <NUM> in the longitudinal direction. Further, the "rear end" in the horizontal axis of <FIG> represents a position on the other end side of the fixing belt <NUM> in the longitudinal direction, e.g., a position of the end on the depth side in <FIG>. <FIG> is a diagram showing the results obtained by measuring the temperature of the press roller <NUM> at a plurality of positions in the longitudinal direction of the press roller <NUM>. The vertical axis of <FIG> represents the temperature of the press roller <NUM>. The horizontal axis of <FIG> represents the position in the longitudinal direction of the press roller <NUM>. The "front end" in the horizontal axis of <FIG> represents a position on one end side of the press roller <NUM> in the longitudinal direction, e.g., a position of the end on the near side of <FIG>. Further, the "center" in the horizontal axis of <FIG> represents a position of the center portion of the press roller <NUM> in the longitudinal direction. Further, the "rear end" in the horizontal axis of <FIG> represents a position on the other end side of the press roller <NUM> in the longitudinal direction, e.g., a position of the end on the depth side in <FIG>. Further, "ΔTB" in <FIG> represents the maximum temperature difference of the press roller <NUM>. <FIG> show the results of the temperature measurement at the time of printing in the same job. <FIG> show the same measurement conditions as in <FIG> except that the control temperature and the print speed are changed to the increased temperature and the reduced speed.

The maximum temperature difference of the press roller <NUM> in the 50th sheet, ΔTB in <FIG>, is reduced as compared with ΔTA in <FIG>. Therefore, the outer diameter difference corresponding to the position of the press roller <NUM> in the longitudinal direction is suppressed to be small as compared with the case where the control temperature and the print speed are set to the standard temperature and the standard speed without change.

<FIG> is a diagram showing the relationship between the control temperature and print speed, and the temperature difference corresponding to the position of the press roller <NUM> in the longitudinal direction. <FIG> shows the cases where the print speeds are <NUM> CPM, <NUM> CPM, and <NUM> CPM. It can be seen from <FIG> that the temperature difference tends to be smaller as the control temperature becomes higher and as the print speed becomes slower. As a result, the temperature difference ΔTB (see <FIG>) is reduced as compared with the temperature difference ΔTA (see <FIG>) as described above.

<FIG> is a diagram showing the relationship between the temperature difference and the outer diameter difference corresponding to the position of the press roller <NUM> in the longitudinal direction. It can be seen from <FIG> that the outer diameter difference tends to be smaller as the temperature difference becomes smaller. Therefore, the temperature difference ΔTA (see <FIG>) is reduced as described above, and thus the outer diameter difference corresponding to the position of the press roller <NUM> in the longitudinal direction is suppressed to be small. In such a manner, according to the MFP <NUM>, the variation in the pressing force corresponding to the position of the press roller <NUM> in the longitudinal direction is reduced, and the possibility that a fixing failure occurs can be reduced.

In addition, the MFP <NUM> does not slow down the print speed if the print sheet used is not a small-width sheet or if it does not perform a large-volume print job. Therefore, the slowdown of the print speed is limited to some jobs and the decrease in productivity is suppressed to a small level.

In addition, if the control temperature and the print speed are set to the increased temperature and the reduced speed prior to the start of printing of one job, the MFP <NUM> maintains the control temperature and the print speed at the increased temperature and the reduced speed until the printing of the job is completed. Therefore, it is possible to reduce the possibility that a fixing failure occurs in all printing of the corresponding job.

<FIG> is a diagram showing the relationship between the control temperature and print speed, and the offset level. <FIG> shows the cases where the print speeds are <NUM> CPM, <NUM> CPM, and <NUM> CPM. It can be seen from <FIG> that the offset level tends to be reduced if the control temperature is increased or the print speed is lowered. Note that the offset level is a level obtained by visually evaluating the effect on the image quality of the residual image, which is caused when a developer adhering to the fixing belt <NUM> from the print sheet adheres again to the print sheet. For example, if the offset level is equal to or less than "OAA", and if the residual image falls within an allowable level, it is effective to set the print speed to be equal to or less than <NUM> CPM.

This embodiment can be variously modified as follows. The processor <NUM> may instruct the printer controller <NUM> to change only the setting of the control temperature in ACT8 of <FIG>. In other words, the print speed may be the standard speed as it is.

In some circumstances, the processor <NUM> may change at least one of the control temperature or the print speed until the completion of printing is confirmed in ACT10 after instructing the start of printing in ACT9 of <FIG>.

The print control processing may be performed by a processor of the printer controller <NUM>.

The fixing unit <NUM> may be changed to have any configuration as long as it has a function of heating and pressing the sheet, such as using a roller instead of the fixing belt <NUM> or, conversely, using a belt instead of the press roller <NUM>.

Claim 1:
An image forming apparatus (<NUM>), configured to perform image formation by forming an image on a sheet and fixing the formed image onto the sheet, comprising:
a heater (<NUM>) configured to generate heat to heat the sheet over an entire region in a direction perpendicular to a conveyance direction of the sheet to fix the image onto the sheet conveyed after the image is formed on the sheet;
a pressing member (<NUM>, <NUM>, <NUM>) configured to apply a pressure for fixing to the sheet heated by the heater (<NUM>) over the entire region in the direction perpendicular to the conveyance direction;
a temperature sensor (<NUM>) configured to directly or indirectly measure a temperature of the pressing member (<NUM>, <NUM>, <NUM>);
a fixing controller (<NUM>) configured to control heat generation of the heater such that the temperature measured by the temperature sensor approaches a control temperature; and
a processor (<NUM>) configured to set, before starting image formation of one job including the image formation,
- one candidate temperature of a plurality of predetermined candidate temperatures different from each other as the control temperature on a basis of the number of sheets to be used and a sheet size to be used in the image formation of the one job, characterised by the processor being further configured to set, before starting the image formation of the one job including the image formation,
- one candidate speed of a plurality of predetermined candidate speeds different from each other as an image forming speed on a basis of the number of sheets to be used and a sheet size to be used in the image formation of the one job,
wherein the processor is configured to set, in a case where a width of the sheet to be used in the direction perpendicular to the conveyance direction is narrower than a predetermined specified width and the number of sheets to be used in image formation of one job including the image formation is larger than a predetermined specified number of sheets,
- a first candidate temperature as the control temperature, which is higher than other candidate temperatures to be set as the control temperature in other cases, and
- a first candidate speed as the image forming speed, which is slower than other candidate speed to be set as the image forming speed in other cases.