Patent Publication Number: US-11385583-B2

Title: Image forming apparatus, image forming method, and image forming program capable of preventing image quality from being lowered

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2020-113417, filed on Jun. 30, 2020, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     The present disclosure relates to an image forming apparatus, an image forming method, and an image forming program, and more specifically to an image forming apparatus in which an elastic body is in pressure contact with an image carrier, and an image forming method and an image forming program executed in the image forming apparatus. 
     Description of the Related Art 
     In an image forming apparatus such as a Multi Function Peripheral (MFP), a toner image on an image carrier is transferred onto a recording medium such as paper to cause an image to be formed on the recording medium. The image carrier is provided so as to be in pressure contact with an elastic body such as a roller. Here, in a case in which the image carrier and the elastic body are left in a stopped state for a long time while being in pressure contact with each other, the surface of the image carrier may be contaminated by a substance (bleed) exuding from the elastic body. In this case, the transferability of the contaminated portion of the image carrier is lowered, and a white spot is thus generated in the formed image. 
     For example, JP 2004-286985 A describes an image forming apparatus at least including a photoconductor, a charging means that charges a surface of the photoconductor at uniform potential, a latent image forming means that forms an image-like electrostatic latent image on the surface of the photoconductor, a developing means that develops the electrostatic latent image by applying toner to the electrostatic latent image to form a toner image, an endless intermediate transfer belt that partially abuts on the surface of the photoconductor, a primary transfer means that transfers the toner image formed on the surface of the photoconductor to a peripheral surface of the intermediate transfer belt at a transfer position at which the photoconductor and the intermediate transfer belt abut on each other, and a second transfer means that transfers the toner image transferred on the peripheral surface of the intermediate transfer belt to a recording medium at a second transfer position different from the transfer position, and the image forming apparatus includes a toner intervening arranging means that arranges the toner so that the toner intervenes at the transfer position at the end of operation of the apparatus. 
     JP 2004-286985 A describes that, since, at the end of operation of the apparatus, the toner is arranged so that the toner intervenes between the photoconductor and the intermediate transfer belt that abut on each other at the transfer position, the photoconductor and the intermediate transfer belt are not in close contact with each other, and contamination of the surface of the photoconductor due to a bleed substance such as a plasticizer is suppressed. However, in a case in which the number of the bleed substances generated is large, the toner in contact with the bleed substances is contaminated, and the bleed substances as well as the toner adhere to the photoconductor. In this case, the surface of the photoconductor is rather contaminated, and the quality of the image formed on the recording medium is lowered. 
     SUMMARY 
     The present disclosure has been made to solve one or more of the above-mentioned problems, and an object of the present disclosure may be to provide an image forming apparatus that can prevent the quality of an image formed on a recording medium from being lowered. 
     Another object of the present disclosure may be to provide an image forming method that can prevent the quality of an image formed on a recording medium from being lowered. 
     Still another object of the present disclosure may be to provide an image forming program that can prevent the quality of an image formed on a recording medium from being lowered. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present disclosure, there is provided an image forming apparatus in which an image carrier and an elastic body may be in pressure contact with each other, and in which a toner remover may be in contact with the image carrier to remove toner remaining on the image carrier. The image forming apparatus reflecting one aspect of the present disclosure may comprise: a first hardware processor that forms an image pattern in a region including at least a part of a pressure contact part of the image carrier that is in pressure contact with the elastic body when operation of the image carrier is stopped; a second hardware processor that acquires density of the image pattern formed on the image carrier by the first hardware processor; a third hardware processor that adjusts driving time of the image carrier based on the density of the image pattern acquired by the second hardware processor; and a fourth hardware processor that drives the image carrier for the driving time adjusted by the third hardware processor at a stage before an image is formed on a recording medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the disclosure will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present disclosure: 
         FIG. 1  is a perspective view illustrating appearance of an MFP according to an embodiment; 
         FIG. 2  is a block diagram illustrating an overview of a hardware configuration of the MFP; 
         FIG. 3  is a schematic side view illustrating a partial internal configuration of an image former and a paper feed unit; 
         FIG. 4  is a diagram illustrating a part of an intermediate transfer belt; 
         FIG. 5  is a diagram illustrating an example of a process for forming an image pattern; 
         FIG. 6  is a diagram illustrating another example of the process for forming an image pattern; 
         FIG. 7  is a diagram illustrating a process for detecting an image pattern; 
         FIG. 8  is a graph illustrating distribution of density of the detected image pattern; 
         FIG. 9  is a graph illustrating a relationship between a density difference of the image pattern and driving time of the intermediate transfer belt; 
         FIG. 10  is a diagram illustrating an example of functions of a CPU in the MFP according to the present embodiment; 
         FIG. 11  is a flowchart illustrating an example of a flow of print processing; 
         FIG. 12  is a graph illustrating another example of the relationship between the density difference of the image pattern and the driving time of the intermediate transfer belt according to a first modification example; 
         FIG. 13  is a table illustrating the relationship between the density difference of the image pattern and the driving time of the intermediate transfer belt according to the first modification example; 
         FIG. 14  is a flowchart illustrating an example of a flow of print processing according to the first modification example; 
         FIG. 15  is a flowchart illustrating an example of a flow of print processing according to a second modification example; 
         FIG. 16  is a table illustrating a relationship between the number of pieces of processing of a secondary transfer roller and removal processing according to a third modification example; 
         FIG. 17  is a diagram illustrating an example of functions of the CPU in the MFP according to the third modification example; 
         FIG. 18  is a flowchart illustrating an example of a flow of print processing according to the third modification example; 
         FIG. 19  is a table illustrating a relationship between operation stop time of the intermediate transfer belt and the removal processing in a fourth modification example; 
         FIG. 20  is a flowchart illustrating an example of a flow of print processing according to the fourth modification example; 
         FIG. 21  is a table illustrating a relationship among the number of pieces of processing of the secondary transfer roller, the operation stop time of the intermediate transfer belt, and the removal processing; 
         FIG. 22  is a diagram illustrating an example of functions of the CPU in the MFP according to a second embodiment; and 
         FIG. 23  is a flowchart illustrating an example of a flow of print processing according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an image forming apparatus according to one or more embodiments of the present disclosure will be described with reference to the drawings. However, the scope of the disclosure is not limited to the disclosed embodiments. In the following description, identical parts are labeled with the same reference signs. Names and functions of these parts are the same. Therefore, detailed description thereof will not be repeated. Also, in the following description, an MFP will be described as an example of the image forming apparatus. Further, in the MFP described below, a recording medium on which an image is formed includes paper such as plain paper, high-quality paper, recycled paper, and photographic paper, and an OverHead Projector (OHP) film. 
     First Embodiment 
       FIG. 1  is a perspective view illustrating appearance of an MFP according to the present embodiment.  FIG. 2  is a block diagram illustrating an overview of a hardware configuration of the MFP. Referring to  FIGS. 1 and 2 , an MFP  100  is an example of an image forming apparatus and includes a main circuit  110 , an original reading unit  130  that reads an original, an automatic original conveying device  120  that conveys the original to the original reading unit  130 , an image former  140  that forms an image on a recording medium based on image data, a paper feed unit  150  that supplies the recording medium to the image former  140 , and an operation panel  160  that serves as a user interface. 
     The automatic original conveying device  120  automatically conveys a plurality of originals set on an original tray  125  one by one to an original reading position of the original reading unit  130  and discharges onto an original discharge tray  127  the original from which an image formed on the original is read by the original reading unit  130 . The automatic original conveying device  120  includes an original detection sensor that detects originals placed on the original tray  125 . 
     The original reading unit  130  includes a rectangular reading surface for reading an original. The reading surface is made of platen glass, for example. The automatic original conveying device  120  is connected to a main body of the MFP  100  to be rotatable about an axis parallel to one side of the reading surface and can be opened and closed. The original reading unit  130  is arranged on a lower side of the automatic original conveying device  120 , and the reading surface of the original reading unit  130  is exposed in an open state in which the automatic original conveying device  120  is rotated and opened. Therefore, the user can place the original over the reading surface of the original reading unit  130 . The state of the automatic original conveying device  120  can be changed into the open state in which the reading surface of the original reading unit  130  is exposed or a closed state in which the reading surface is covered. The automatic original conveying device  120  includes a state detection sensor that detects the open state of the automatic original conveying device  120 . 
     The original reading unit  130  includes a light source that emits light and a photoelectric conversion element that receives light and scans an image formed on the original placed on the reading surface. In a case in which the original is placed in a reading region, light emitted from the light source is reflected by the original, and the reflected light is imaged by the photoelectric conversion element. When the photoelectric conversion element receives the light reflected by the original, the photoelectric conversion element generates image data obtained by converting the received light into an electric signal. The original reading unit  130  outputs the image data to a Central Processing Unit (CPU)  111  included in the main circuit  110 . 
     The paper feed unit  150  takes out a recording medium housed in any of a plurality of paper feed trays or a manual feed tray and conveys the recording medium to the image former  140 . 
     The image former  140  is controlled by the CPU  111  and forms an image on the recording medium conveyed by the paper feed unit  150  by a known electrophotographic method. In the present embodiment, the image former  140  forms an image of the image data input from the CPU  111  on the recording medium conveyed by the paper feed unit  150 . The recording medium on which the image is formed is discharged to a paper discharge tray  159 . The image data output by the CPU  111  to the image former  140  includes image data input from the original reading unit  130  and image data received from an outside such as print data. 
     The main circuit  110  includes the CPU  111  that controls the entire MFP  100 , a communication interface (I/F) unit  112 , Read Only Memory (ROM)  113 , Random Access Memory (RAM)  114 , a hard disc drive (HDD)  115  serving as a large-capacity storage device, a facsimile unit  116 , and an external storage device  118 . The CPU  111  is connected to the automatic original conveying device  120 , the original reading unit  130 , the image former  140 , the paper feed unit  150 , and the operation panel  160  and controls the entire MFP  100 . 
     The ROM  113  stores a program executed by the CPU  111  or data required to execute the program. The RAM  114  is used as a work area when the CPU  111  executes a program. Also, the RAM  114  temporarily stores image data continuously transmitted from the original reading unit  130 . 
     The operation panel  160  is provided on the top of the MFP  100 . The operation panel  160  includes a display unit  161  and an operation unit  163 . The display unit  161  is a liquid crystal display (LCD), for example, and displays an instruction menu to the user, information about acquired image data, and the like. Note that the LCD can be replaced with any device that displays an image such as an organic electroluminescence (EL) display. 
     The operation unit  163  includes a touch panel  165  and a hard key unit  167 . The touch panel  165  is of a capacitive type. Note that the touch panel  165  can be of another type such as a resistive type, a surface acoustic wave type, an infrared type, and an electromagnetic resonance type instead of the capacitive type. 
     The touch panel  165  is provided on the display unit  161  with a detection surface thereof superposed on the upper surface or the lower surface of the display unit  161 . Here, the size of the detection surface of the touch panel  165  and the size of the display surface of the display unit  161  are the same. Therefore, the coordinate system of the display surface and the coordinate system of the detection surface are the same. The touch panel  165  detects on the detection surface a position on the display surface of the display unit  161  that the user indicates and outputs the coordinates of the detected position to the CPU  111 . Since the coordinate system of the display surface and the coordinate system of the detection surface are the same, the coordinates output by the touch panel  165  can be replaced with the coordinates on the display surface. 
     The hard key unit  167  includes a plurality of hard keys. An example of the hard keys is a contact switch. The touch panel  165  detects a position on the display surface of the display unit  161  indicated by the user. Since the user operates the MFP  100  with an upright posture in many cases, the display surface of the display unit  161 , the operation surface of the touch panel  165 , and the hard key unit  167  are arranged facing upward. The reason for this is that the user can easily visually recognize the display surface of the display unit  161  and can easily indicate the operation unit  163  with a finger. 
     The communication I/F unit  112  is an interface for connecting the MFP  100  to a network. The communication I/F unit  112  communicates with another computer or a data processing device connected to the network by means of a communication protocol such as Transmission Control Protocol (TCP) and File Transfer Protocol (FTP). Note that the network to which the communication I/F unit  112  is connected is a local area network (LAN), and the connection form may be wired or wireless. The network is not limited to the LAN and may be a wide area network (WAN), a public switched telephone network (PSTN), the Internet, or the like. 
     The facsimile unit  116  is connected to the public switched telephone network (PSTN) and transmits facsimile data to the PSTN or receives facsimile data from the PSTN. The facsimile unit  116  stores received facsimile data in the HDD  115 , converts the facsimile data into print data that can be printed in the image former  140 , and outputs the print data to the image former  140 . As a result, the image former  140  forms an image of the facsimile data received from the facsimile unit  116  on paper. The facsimile unit  116  also converts data stored in the HDD  115  into facsimile data and transmits the facsimile data to a facsimile device connected to the PSTN. 
     The external storage device  118  is controlled by the CPU  111  and causes Compact Disc Read Only Memory (CD-ROM)  118 A or semiconductor memory to be mounted therein. In the present embodiment, although an example in which the CPU  111  executes a program stored in the ROM  113  will be described, the CPU  111  may control the external storage device  118 , read a program to be executed by the CPU  111  from the CD-ROM  118 A, store the read program in the RAM  114 , and execute the program. 
     Note that the recording medium that stores the program to be executed by the CPU  111  is not limited to the CD-ROM  118 A and may be a medium such as a flexible disc, a cassette tape, an optical disc (Magnetic Optical Disc (MO), Mini Disc (MD), or Digital Versatile Disc (DVD)), an IC card, an optical card, mask ROM, and semiconductor memory such as Erasable Programmable ROM (EPROM). Further, the CPU  111  may download a program from a computer connected to the network and store the program in the HDD  115  or cause the computer connected to the network to write the program in the HDD  115  and load onto the RAM  114  and execute the program stored in the HDD  115 . The program referred to here includes not only a program that can directly be executed by the CPU  111  but also a source program, a compressed program, an encrypted program, and the like. 
       FIG. 3  is a schematic side view illustrating a partial internal configuration of the image former and the paper feed unit. Referring to  FIG. 3 , inside the MFP  100 , a main conveyance path  41  indicated by the thick dotted arrow is formed so as to extend basically in an up-down direction. The main conveyance path  41  is a path for guiding paper conveyed from the paper feed unit  150  through the image former  140  to the paper discharge tray  159 . In the main conveyance path  41  in the present example, a lower end  30  on the opposite side of an upper end  13  located further on the upper side than the image former  140  constitutes a carry-in port that receives paper from the paper feed unit  150 . Also, the upper end  13  of the main conveyance path  41  constitutes a discharge port that discharges the paper on which an image has been formed to the paper discharge tray  159 . The upper end  13  of the main conveyance path  41  is provided with a paper discharge roller  15 . 
     The paper feed unit  150  includes three paper feed trays  151 ,  152 , and  153  and a manual feed tray  154 . The three paper feed trays  151 ,  152 , and  153  are stacked so as to be arranged from the upper side to the lower side in this order. The manual feed tray  154  is provided on a sidewall of the MFP  100  and is located further on the lower side than the image former  140 . As illustrated by the thick dashed-dotted lines in  FIG. 3 , the paper feed trays  151 ,  152 , and  153  and the manual feed tray  154  are connected to the lower end  30  of the main conveyance path  41  through sub conveyance paths SP 1 , SP 2 , SP 3 , and SP 4 , respectively. 
     Pickup rollers  151   p ,  152   p ,  153   p , and  154   p  are provided corresponding to the paper feed trays  151 ,  152 , and  153  and the manual feed tray  154 , respectively. Since operations of taking out the recording media from the paper feed trays  151 ,  152 , and  153  and the manual feed tray  154  and conveying the recording media are the same, an operation of the paper feed tray  151  will be described here as an example. 
     In the paper feed tray  151 , one or more recording media are stored in a stacked state. The paper feed tray  151  has a lift-up mechanism that pushes up one or more recording media housed therein. The pickup roller  151   p  is biased by an elastic member such as a spring so as to abut from above on the uppermost recording medium out of one or more recording media housed in the paper feed tray  151 . The pickup roller  151   p  presses from above the recording medium. As the pickup roller  151   p  rotates, the uppermost recording medium is fed to the sub conveyance path SP 1  due to a frictional force with the recording medium. The recording medium fed to the sub conveyance path SP 1  is supplied to the main conveyance path  41 . 
     In the MFP  100 , at the time of image formation, a tray that houses a recording medium to be image-formed is selected as a target tray from the three paper feed trays  151 ,  152 , and  153  and the manual feed tray  154 . The pickup roller and the paper feed roller corresponding to the tray selected as the target tray from among the three paper feed trays  151 ,  152 , and  153  and the manual feed tray  154  are operated to cause the recording medium to be supplied from the tray selected as the target tray through any of the sub conveyance paths SP 1 , SP 2 , SP 3 , and SP 4  to the main conveyance path  41 . 
     The image former  140  employs an intermediate transfer method and includes image forming units  51 Y,  51 M,  51 C, and  51 K for yellow, magenta, cyan, and black, respectively. At least one of the image forming units  51 Y,  51 M,  51 C, and  51 K is driven to cause an image to be formed on the recording medium. All of the image forming units  51 Y,  51 M,  51 C, and  51 K are driven to cause a full-color image to be formed. The image forming units  51 Y,  51 M,  51 C, and  51 K are provided with printing data of yellow, magenta, cyan, and black, respectively. Since the image forming units  51 Y,  51 M,  51 C, and  51 K differ only in the colors of the toners they handle, the image forming unit  51 Y for forming a yellow image will be described here. 
     The image forming unit  51 Y includes an exposure head  52 Y into which yellow printing data is input, a photoconductor drum  53 Y serving as an example of an image carrier, a charging roller  54 Y, a developing roller  55 Y, and a primary transfer roller  56 Y. The exposure head  52 Y emits laser light corresponding to the received printing data (electric signal). The emitted laser light is one-dimensionally scanned by a polygon mirror included in the exposure head  52 Y and exposes the photoconductor drum  53 Y. The one-dimensional scanning direction for the photoconductor drum  53 Y is a main scanning direction. The charging roller  54 Y is an elastic body and is arranged so as to be in pressure contact with the photoconductor drum  53 Y. The photoconductor drum  53 Y is charged by the charging roller  54 Y and then irradiated with the laser light emitted by the exposure head  52 Y. As a result, an electrostatic latent image is formed on the photoconductor drum  53 Y. Subsequently, the developing roller  55 Y places toner on the electrostatic latent image to form a toner image. The toner image formed on the photoconductor drum  53 Y is transferred onto an intermediate transfer belt  57  (image carrier) by the primary transfer roller  56 Y. 
     Similarly, the image forming unit  51 M includes an exposure head  52 M into which magenta printing data is input, a photoconductor drum  53 M, a charging roller  54 M, a developing roller  55 M, and a primary transfer roller  56 M. The image forming unit  51 C includes an exposure head  52 C into which cyan printing data is input, a photoconductor drum  53 C, a charging roller  54 C, a developing roller  55 C, and a primary transfer roller  56 C. The image forming unit  51 K includes an exposure head  52 K into which black printing data is input, a photoconductor drum  53 K, a charging roller  54 K, a developing roller  55 K, and a primary transfer roller  56 K. 
     The intermediate transfer belt  57  is an example of an image carrier and is suspended by a driving roller  54  and a roller  54 A so as not to be loosened. When the driving roller  54  is rotated counterclockwise in the drawing, the intermediate transfer belt  57  is rotated counterclockwise in the drawing at predetermined speed. As the intermediate transfer belt  57  is rotated, the roller  54 A is rotated counterclockwise. 
     As a result, the image forming units  51 Y,  51 M,  51 C, and  51 K sequentially transfer toner images onto the carrying surface of the intermediate transfer belt  57 . The intermediate transfer belt  57  carries the toner images transferred on the carrying surface. A time at which each of the image forming units  51 Y,  51 M,  51 C, and  51 K transfers the toner image onto the intermediate transfer belt  57  is adjusted by detecting a reference mark attached to the intermediate transfer belt  57 . As a result, yellow, magenta, cyan, and black toner images are superposed on the intermediate transfer belt  57 . 
     Also, the image former  140  includes an Image Density Control (IDC) sensor  58 . The IDC sensor  58  is a light intensity sensor including a reflective photo sensor, for example, and detects a toner image formed on the intermediate transfer belt  57  by detecting the intensity of the reflected light from the surface of the intermediate transfer belt  57 . The detection result output by the IDC sensor  58  is used for image stabilization processing. The image stabilization processing is processing for determining a control value for use in control of the image former  140 . Specifically, the image stabilization processing is processing for causing the image former  140  to form a patch image determined in advance on the intermediate transfer belt  57  and determining a control value based on a measurement result obtained by measuring the density of the patch image. The control value includes voltage applied to the charging rollers  54 Y,  54 M,  54 C, and  54 K, bias voltage applied to the developing rollers  55 Y,  55 M,  55 C, and  55 K, primary transfer voltage applied to the primary transfer rollers  56 Y,  56 M,  56 C, and  56 K, and secondary transfer voltage applied to a secondary transfer roller  47 . 
     Further, the image former  140  includes a cleaning blade  59 . The cleaning blade  59  is made of a urethane-rubber-based elastic body, for example, and is arranged to enable the intermediate transfer belt  57  to be rubbed. The cleaning blade  59  cleans the intermediate transfer belt  57  by scraping off the toner image remaining on the intermediate transfer belt  57  as the intermediate transfer belt  57  is rotated. 
     On the main conveyance path  41 , a timing roller  45 , the secondary transfer roller  47 , and a fixing roller  49  are arranged to be spaced from each other in this order from the lower end  30  to the upper end  13 . The secondary transfer roller  47  is made of an elastic body such as foam rubber and is in pressure contact with the roller  54 A with the intermediate transfer belt  57  interposed therebetween. Note that, in the present example, the MFP  100  does not have a pressure contact separation mechanism for switching between a pressure contact state and a separation state of the intermediate transfer belt  57  and the secondary transfer roller  47 . Therefore, the cost of the MFP  100  can be reduced, and the size thereof can be reduced. A recording medium supplied from the paper feed unit  150  to the main conveyance path  41  is sent to the timing roller  45 . 
     The timing roller  45  adjusts a conveying state of the recording medium on the main conveyance path  41  so that the recording medium reaches a position between the roller  54 A and the secondary transfer roller  47  at a time when the toner image formed on the intermediate transfer belt  57  reaches the position between the roller  54 A and the secondary transfer roller  47 . The recording medium conveyed by the timing roller  45  is pressed against the intermediate transfer belt  57  by the secondary transfer roller  47 , and by charging the secondary transfer roller  47 , a yellow, magenta, cyan, or black toner image superposed and formed on the intermediate transfer belt  57  is transferred to the recording medium. The voltage applied to the secondary transfer roller  47  is controlled by the CPU  111  so that the charge amount of the secondary transfer roller  47  has a value suitable for the basis weight of the recording medium. 
     The recording medium on which the toner image is transferred is conveyed to the fixing roller  49  and heated by the fixing roller  49 . As a result, the toner is melted and fixed on the recording medium. Thereafter, the recording medium on which the image has been formed is discharged from the upper end  13  of the main conveyance path  41  onto the paper discharge tray  159  by the paper discharge roller  15 . The temperature of the fixing roller  49  is controlled by the CPU  111  so as to have a value suitable for the basis weight of the recording medium. 
       FIG. 4  is a diagram illustrating a part of the intermediate transfer belt. Referring to  FIG. 4 , a surface portion of the intermediate transfer belt  57  that is in pressure contact with the secondary transfer roller  47  when the operation of the intermediate transfer belt  57  is stopped is referred to as a pressure contact part  57 A. A surface portion of the intermediate transfer belt  57  that is not in pressure contact with the secondary transfer roller  47  when the operation of the intermediate transfer belt  57  is stopped, that is, a portion on the surface of the intermediate transfer belt  57  other than the pressure contact part  57 A is referred to as a non-pressure contact part  57 B. In  FIG. 4  and the subsequent figures, the pressure contact part  57 A of the intermediate transfer belt  57  is illustrated by a hatched pattern, and the non-pressure contact part  57 B is illustrated in white. In a case in which the operation stop time of the intermediate transfer belt  57  is long, the pressure contact part  57 A may be contaminated by a substance (bleed) exuding from the secondary transfer roller  47 . 
     In particular, in a case in which the secondary transfer roller  47  is made of foam rubber containing various additives as in the present example, the bleed is likely to be generated, and the degree of contamination of the pressure contact part  57 A thus increases. Also, in order to ensure the transferability of the toner image from the intermediate transfer belt  57  to the recording medium, the intermediate transfer belt  57  and the secondary transfer roller  47  may be strongly pressed against each other. The stronger the force by which the intermediate transfer belt  57  and the secondary transfer roller  47  are pressed, the longer the pressure contact width (nip width). The nip width is a length of the pressure contact part  57 A in a driving direction of the intermediate transfer belt  57 . In this case, the degree of contamination of the pressure contact part  57 A tends to increase. Note that, in the present example, the nip width is A 1 . 
     Since the surface properties of the pressure contact part  57 A contaminated by the bleed change, the transfer rate on the pressure contact part  57 A is different from the transfer rate on the non-pressure contact part  57 B. Therefore, in a case in which the exposure amounts are equal, a difference occurs between the amount of toner transferred to the pressure contact part  57 A and that transferred to the non-pressure contact part  57 B. Therefore, a difference occurs between the density of the toner image formed on the pressure contact part  57 A and that on the non-pressure contact part  57 B. The higher the degree of contamination of the pressure contact part  57 A due to the bleed, the greater the difference between the density of the toner image on the pressure contact part  57 A and that on the non-pressure contact part  57 B. 
       FIG. 5  is a diagram illustrating an example of a process for forming an image pattern. In order to prevent the above phenomenon, referring to  FIG. 5 , before forming the toner image to be formed on the recording medium, an image pattern GP is formed in a region including at least a part of the pressure contact part  57 A and at least a part of the non-pressure contact part  57 B of the intermediate transfer belt  57 . The image pattern GP is a toner image formed on the intermediate transfer belt  57  with the exposure amounts of the photoconductor drums  53 Y,  53 M,  53 C, and  53 K equal and is different from the toner image to be formed on the recording medium. In  FIG. 5  and the subsequent figures, the image pattern GP is illustrated as a dot pattern. 
     In the present example, the width of the image pattern GP in the driving direction of the intermediate transfer belt  57  is A 2 , which is longer than the nip width A 1 . Also, in the present example, the width of the image pattern GP formed in the direction perpendicular to the driving direction of the intermediate transfer belt  57  is W 1 , which is approximately equal to W 2 , which is the width of a detection region detected by the IDC sensor  58 , and the embodiment is not limited to this.  FIG. 6  is a diagram illustrating another example of the process for forming an image pattern. Referring to  FIG. 6 , the width of the image pattern GP formed is W 3  and may be longer than the width W 2 , which is the detection region detected by the IDC sensor  58 . 
       FIG. 7  is a diagram illustrating a process for detecting an image pattern. Referring to  FIG. 7 , the intermediate transfer belt  57  is driven (rotated) so that the portion in which the image pattern GP is formed passes through the detection region detected by the IDC sensor  58 . Thereafter, the image pattern GP is detected by the IDC sensor  58 . 
       FIG. 8  is a graph illustrating the distribution of the density of the detected image pattern. Referring to  FIG. 8 , in a case in which the degree of contamination of the pressure contact part  57 A is high, the amount of toner in the image pattern GP in the pressure contact part  57 A is smaller than the amount of toner in the image pattern GP in the non-pressure contact part  57 B. Therefore, the density of the image pattern GP in the pressure contact part  57 A is lower than the density of the image pattern GP in the non-pressure contact part  57 B. Accordingly, the density of the image pattern GP in the pressure contact part  57 A and that in the non-pressure contact part  57 B are detected, and a density difference ΔE of the image pattern GP between the portions is acquired. 
     The acquired density difference ΔE is compared with a predetermined density threshold value. The density threshold value is a value obtained by experiments in consideration of the influence of contamination of the intermediate transfer belt  57  due to the bleed on the image quality. In a case in which the density difference ΔE is lower than the density threshold value, it is determined that the pressure contact part  57 A is not contaminated. On the other hand, in a case in which the density difference ΔE is equal to or higher than the density threshold value, it is determined that the pressure contact part  57 A is contaminated, and the intermediate transfer belt  57  is driven for a predetermined time before forming an image on the recording medium. During this period, the bleed adhering to the pressure contact part  57 A is gradually removed by rubbing with the cleaning blade  59 . This can prevent the quality of the image formed on the recording medium from being lowered.  FIG. 9  is a graph illustrating the relationship between the density difference of the image pattern and the driving time of the intermediate transfer belt. Referring to  FIG. 9 , as the driving time of the intermediate transfer belt  57  is longer, the amount of bleed to be removed is larger, and the density difference ΔE of the image pattern GP formed on the intermediate transfer belt  57  is thus lowered. 
       FIG. 10  is a diagram illustrating an example of the functions of the CPU in the MFP according to the present embodiment. The functions illustrated in  FIG. 10  are functions fulfilled by the CPU  111  included in the MFP  100  as the CPU  111  executes a recording medium conveying program stored in the ROM  113 , the HDD  115 , or the CD-ROM  118 A. Referring to  FIG. 10 , the CPU  111  includes a print reception unit  210 , a pattern forming unit  220 , a density acquisition unit  230 , a driving time adjustment unit  240 , a driving execution unit  250 , and a print execution unit  260 . The print reception unit  210  receives an instruction to execute print from the user. 
     The pattern forming unit  220  forms the image pattern GP in a region including at least a part of the pressure contact part  57 A and at least a part of the non-pressure contact part  57 B of the intermediate transfer belt  57  before execution of print. 
     Specifically, the pattern forming unit  220  includes a region specifying unit  221 , a driving control unit  222 , and a unit control unit  223 . The region specifying unit  221  specifies a region in which the image pattern GP is to be formed including at least a part of the pressure contact part  57 A and at least a part of the non-pressure contact part  57 B in response to the print reception unit  210  receiving the instruction to execute print. The region in which the image pattern GP is to be formed preferably bridges over the pressure contact part  57 A in the front-rear direction in the driving direction of the intermediate transfer belt  57 . In this case, the density difference of the image pattern GP between the pressure contact part  57 A and the non-pressure contact part  57 B can be obtained easily since, in a case in which the pressure contact part  57 A is contaminated, the density of the image pattern GP in the pressure contact part  57 A and that in the non-pressure contact part  57 B located at the front and rear of the pressure contact part  57 A will differ significantly in a later process. 
     The driving control unit  222  controls the operation of the intermediate transfer belt  57  so that the region specified by the region specifying unit  221  moves to an image forming region for any image forming unit (hereinbelow referred to as an image pattern forming unit) out of the image forming units  51 Y,  51 M,  51 C, and  51 K. In a case in which the intermediate transfer belt  57  is provided with a reference mark such as a position detection mark in advance, the operation of the intermediate transfer belt  57  may be controlled based on the reference mark. Alternatively, since a positional relationship between the secondary transfer roller  47  and the image pattern forming unit is known, the operation of the intermediate transfer belt  57  may be controlled based on the positional relationship. 
     The unit control unit  223  controls the operation of the image pattern forming unit to cause the image pattern GP to be formed in the region specified by the region specifying unit  221 . The image pattern GP is preferably formed with relatively low density. As a result, in a later process, the density difference of the image pattern GP can be obtained more easily than in a case in which the image pattern GP is formed with maximum density (solid density) or relatively high density. 
     The image pattern GP is preferably formed in a region in which at least a part of the pressure contact part  57 A and at least a part of the non-pressure contact part  57 B are continuous. According to this configuration, in a case in which the pressure contact part  57 A is contaminated, the density of the image pattern GP differs significantly at a boundary portion between the pressure contact part  57 A and the non-pressure contact part  57 B. Therefore, the density difference of the image pattern GP between the pressure contact part  57 A and the non-pressure contact part  57 B can be obtained easily. However, the image pattern GP may be formed in each of at least a part of the pressure contact part  57 A and at least a part of the non-pressure contact part  57 B. In this case, the region in at least the part of the pressure contact part  57 A and the region in at least the part of the non-pressure contact part  57 B may be separated from each other. 
     The density acquisition unit  230  acquires the density distribution of the image pattern GP formed by the pattern forming unit  220 . Specifically, the density acquisition unit  230  includes a driving control unit  231 , an image data acquisition unit  232 , a pressure contact density detection unit  233 , a non-pressure contact density detection unit  234 , and a density difference calculation unit  235 . After the image pattern GP is formed by the unit control unit  223 , the driving control unit  231  controls the operation of the intermediate transfer belt  57  so that the region of the image pattern GP specified by the region specifying unit  221  passes through the detection region detected by the IDC sensor  58 . In a case in which the intermediate transfer belt  57  is provided with a reference mark such as a position detection mark in advance, the operation of the intermediate transfer belt  57  may be controlled based on the reference mark. Alternatively, since a positional relationship between the image pattern forming unit and the IDC sensor  58  is known, the operation of the intermediate transfer belt  57  may be controlled based on the positional relationship. 
     The region of the image pattern GP passes through the detection region detected by the IDC sensor  58  to cause the image pattern GP to be detected by the IDC sensor  58 , and image data indicating the image of the image pattern GP is generated. The image data acquisition unit  232  acquires the image data of the image pattern GP from the IDC sensor  58 . In the present example, the image pattern GP is detected by the IDC sensor  58  for image stabilization processing, but the embodiment is not limited to this. The image pattern GP may be detected by a sensor provided separately from the IDC sensor  58 . In this case, the image data acquisition unit  232  acquires the image data of the image pattern GP from the sensor. 
     The pressure contact density detection unit  233  detects the density of the image pattern GP in the pressure contact part  57 A based on the image data acquired by the image data acquisition unit  232 . The density of the image pattern GP in the pressure contact part  57 A is detected as an average value of the density in a portion in the image data over the width A 1  in which the density is low, for example. 
     The non-pressure contact density detection unit  234  detects the density of the image pattern GP in the non-pressure contact part  57 B based on the image data acquired by the image data acquisition unit  232 . The density of the image pattern GP in the non-pressure contact part  57 B is detected as an average value of the density in the image data except the density portion over the width A 1 , for example. The density difference calculation unit  235  calculates a difference between the density detected by the pressure contact density detection unit  233  and the density detected by the non-pressure contact density detection unit  234 . As a result, the density difference ΔE of the image pattern GP is acquired. 
     Note that the density of the image pattern GP in the pressure contact part  57 A may be detected as minimum density of the image pattern GP, and the density of the image pattern GP in the non-pressure contact part  57 B may be detected as maximum density of the image pattern GP. In this case, since it is not necessary to distinguish between the portion corresponding to the pressure contact part  57 A and the portion corresponding to the non-pressure contact part  57 B in the image pattern GP, the density difference ΔE of the image pattern GP can be obtained easily. 
     The driving time adjustment unit  240  adjusts the driving time of the intermediate transfer belt  57  based on the density difference ΔE acquired by the density acquisition unit  230 . Specifically, the driving time adjustment unit  240  includes a threshold value acquisition unit  241 , an execution determination unit  242 , and a driving time determination unit  243 . The threshold value acquisition unit  241  acquires a density threshold value stored in advance in the HDD  115  or the like. 
     The execution determination unit  242  compares the density difference ΔE calculated by the density difference calculation unit  235  with the density threshold value acquired by the threshold value acquisition unit  241  and determines whether or not to drive the intermediate transfer belt  57  based on the comparison result. In a case in which the density difference ΔE is lower than the density threshold value, it is determined that the intermediate transfer belt  57  is not to be driven. In a case in which the density difference ΔE is equal to or higher than the density threshold value, it is determined that the intermediate transfer belt  57  is to be driven. 
     In a case in which it is determined by the execution determination unit  242  that the intermediate transfer belt  57  is not to be driven, the driving time determination unit  243  sets the driving time of the intermediate transfer belt  57  to 0. In a case in which it is determined by the execution determination unit  242  that the intermediate transfer belt  57  is to be driven, the driving time determination unit  243  sets the driving time of the intermediate transfer belt  57  to a predetermined time T. Note that T is a value higher than 0. As a result, the driving time of the intermediate transfer belt  57  is adjusted. 
     The driving execution unit  250  controls the operation of the intermediate transfer belt  57  at a stage before the image is formed on the recording medium by the print execution unit  260  to execute driving of the intermediate transfer belt  57  for the driving time adjusted by the driving time adjustment unit  240 . Specifically, in a case in which the driving time of the intermediate transfer belt  57  is set to 0 by the driving time determination unit  243 , the driving execution unit  250  does not execute driving of the intermediate transfer belt  57 . In a case in which the driving time of the intermediate transfer belt  57  is set to T by the driving time determination unit  243 , the driving execution unit  250  executes driving of the intermediate transfer belt  57  for the driving time T. As a result, the bleed adhering to the pressure contact part  57 A can be removed by the cleaning blade  59 . 
     The driving execution unit  250  may further control the image former  140  so that the toner is transferred to the intermediate transfer belt  57  at the time of executing driving of the intermediate transfer belt  57 . In this case, the lubricity between the cleaning blade  59  and the intermediate transfer belt  57  is improved to enable the cleaning blade  59  to be prevented from being rolled up or worn. In addition, the bleed can efficiently be removed by a composition such as an abrasive contained in the toner. Note that a similar effect can be obtained in a case in which a sufficiently large image pattern GP is formed on the intermediate transfer belt  57  as in the example in  FIG. 6 . 
     The print execution unit  260  executes print on the recording medium by controlling the image former  140  and the paper feed unit  150  after the driving execution unit  250  executes driving of the intermediate transfer belt  57 . 
       FIG. 11  is a flowchart illustrating an example of a flow of print processing. The print processing is processing executed by the CPU  111  included in the MFP  100  as the CPU  111  executes a print processing program. Referring to  FIG. 11 , the CPU  111  included in the MFP  100  determines whether or not a print execution instruction has been received (step S 01 ). A standby state is continued until the print execution instruction is received (NO in step S 01 ), and in a case in which the print execution instruction is received (YES in step S 01 ), the processing proceeds to step S 02 . 
     In step S 02 , a region including at least a part of the pressure contact part  57 A and at least a part of the non-pressure contact part  57 B of the intermediate transfer belt  57  is specified as a region in which the image pattern GP is to be formed, and the processing proceeds to step S 03 . In step S 03 , the image pattern GP is formed in the specified region by the image pattern forming unit, and the processing proceeds to step S 04 . In step S 04 , image data of the image pattern GP is acquired from the IDC sensor  58 , and the processing proceeds to step S 05 . 
     In step S 05 , the density of the image pattern GP in the pressure contact part  57 A is detected based on the image data, and the processing proceeds to step S 06 . In step S 06 , the density of the image pattern GP in the non-pressure contact part  57 B is detected based on the image data, and the processing proceeds to step S 07 . In step S 07 , the density difference ΔE of the image pattern GP between the pressure contact part  57 A and the non-pressure contact part  57 B is calculated, and the processing proceeds to step S 08 . 
     In step S 08 , a density threshold value is acquired, and the processing proceeds to step S 09 . In step S 09 , it is determined whether or not the density difference ΔE of the image pattern GP is equal to or higher than the density threshold value. In a case in which the density difference ΔE of the image pattern GP is equal to or higher than the density threshold value, the processing proceeds to step S 10 , and otherwise, the processing proceeds to step S 12 . 
     In step S 10 , the driving time of the intermediate transfer belt  57  is set to T, and the processing proceeds to step S 11 . In step S 11 , the intermediate transfer belt  57  is driven for the set driving time T, and the processing proceeds to step S 12 . In step S 12 , print is executed in accordance with the print execution instruction, and the print processing ends. 
     First Modification Example 
     In a case in which the degree of contamination of the pressure contact part  57 A is low, that is, in a case in which the density difference ΔE of the image pattern GP is low, the driving time of the intermediate transfer belt  57  is preferably short. On the other hand, in a case in which the degree of contamination of the pressure contact part  57 A is high, that is, in a case in which the density difference ΔE of the image pattern GP is high, the driving time of the intermediate transfer belt  57  is preferably long. Therefore, the driving time of the intermediate transfer belt  57  may be determined in accordance with the magnitude of the density difference ΔE of the image pattern GP. 
       FIG. 12  is a graph illustrating another example of the relationship between the density difference of the image pattern and the driving time of the intermediate transfer belt according to a first modification example.  FIG. 13  is a table illustrating the relationship between the density difference of the image pattern and the driving time of the intermediate transfer belt according to the first modification example Referring to  FIGS. 12 and 13 , in the present example, a first density threshold value ΔE 0 , a second density threshold value ΔEa, and a third density threshold value ΔEb are provided. The third density threshold ΔEb is higher than the second density threshold ΔEa, and the second density threshold ΔEa is higher than the first density threshold ΔE 0 . 
     In a case in which the density difference ΔE of the image pattern GP is equal to or lower than the first density threshold value ΔE 0 , it is unknown whether or not the density difference ΔE is caused by the bleed. In this case, no driving time of the intermediate transfer belt  57  is set. In a case in which the density difference ΔE of the image pattern GP is higher than the first density threshold value ΔE 0  and equal to or lower than the second density threshold value ΔEa, the driving time is set to Ta. In a case in which the density difference ΔE of the image pattern GP is higher than the second density threshold value ΔEa and equal to or lower than the third density threshold value ΔEb, the driving time is set to Tb, which is longer than Ta. 
     The relationship between the density difference ΔE of the image pattern GP and the driving time of the intermediate transfer belt  57  may be stored in advance in the HDD  115  or the like as a table as illustrated in  FIG. 12 . Alternatively, a mathematical formula expressing the relationship between the density difference ΔE of the image pattern GP and the driving time of the intermediate transfer belt  57  may be stored in advance in the HDD  115  or the like. 
       FIG. 14  is a flowchart illustrating an example of a flow of print processing according to the first modification example. The print processing in  FIG. 14  is similar to the print processing in  FIG. 11  except that step S 08  is changed to step S 08 A, step S 09  is changed to steps S 09 A and S 09 B, step S 10  is changed to steps S 10 A and S 10 B, and step S 11  is changed to steps S 11 A and S 11 B. Since the other steps are equal to those illustrated in  FIG. 11 , the description thereof will not be repeated here. 
     In step S 08 A, the first density threshold value ΔE 0 , the second density threshold value ΔEa, and the third density threshold value ΔEb are acquired, and the processing proceeds to step S 09 A. In step S 09 A, it is determined whether or not the density difference ΔE of the image pattern GP is higher than the second density threshold value ΔEa and equal to or lower than the third density threshold value ΔEb. In a case in which the density difference ΔE of the image pattern GP is higher than the second density threshold value ΔEa and equal to or lower than the third density threshold value ΔEb, the processing proceeds to step S 10 A, and otherwise, the processing proceeds to step S 09 B. 
     In step S 09 B, it is determined whether or not the density difference ΔE of the image pattern GP is higher than the first density threshold value ΔE 0  and equal to or lower than the second density threshold value ΔEa. In a case in which the density difference ΔE of the image pattern GP is higher than the first density threshold value ΔE 0  and is equal to or lower than the second density threshold value ΔEa, the processing proceeds to step S 10 B, and otherwise (in a case in which the density difference ΔE is equal to or lower than the first density threshold value ΔE 0 ), the processing proceeds to step S 12 . 
     In step S 10 A, the driving time of the intermediate transfer belt  57  is set to Tb, and the processing proceeds to step S 11 A. In step S 11 A, the intermediate transfer belt  57  is driven for the set driving time Tb, and the processing proceeds to step S 12 . In step S 10 B, the driving time of the intermediate transfer belt  57  is set to Ta, and the processing proceeds to step S 11 B. In step S 11 B, the intermediate transfer belt  57  is driven for the set driving time Ta, and the processing proceeds to step S 12 . According to the present example, since the driving time is determined in accordance with the degree of contamination of the pressure contact part  57 A of the intermediate transfer belt  57 , foreign matters can efficiently be removed from the intermediate transfer belt  57 . 
     Second Modification Example 
     In a case in which the density difference ΔE of the image pattern GP is high, such as a case in which the degree of contamination of the pressure contact part  57 A is high, the bleed adhering to the pressure contact part  57 A cannot completely be removed even in a case in which the intermediate transfer belt  57  is driven for a predetermined time T in some cases. Therefore, the driving of the intermediate transfer belt  57  may be repeated until the degree of contamination of the pressure contact part  57 A is equal to or lower than an allowable value. 
       FIG. 15  is a flowchart illustrating an example of a flow of print processing according to a second modification example. The print processing in  FIG. 15  is similar to the print processing in  FIG. 11  except that the processing in step S 11  differs. Since the other steps are equal to those illustrated in  FIG. 11 , the description thereof will not be repeated here. The print processing in the present example may be combined with the print processing according to the first modification example. 
     In step S 11 , the intermediate transfer belt  57  is driven for the set driving time T, and the processing proceeds to step S 03  instead of step S 12 . In this case, steps S 03  to S 09  are executed again. Steps S 03  to S 11  are repeated until it is determined in step S 09  that the density difference ΔE of the image pattern GP is lower than the density threshold value, that is, until it is determined that the degree of contamination is equal to or lower than the allowable value. This can more reliably prevent the pressure contact part  57 A from being contaminated due to the bleed. 
     Third Modification Example 
     The amount of the bleed component contained in the secondary transfer roller  47  is larger as the secondary transfer roller  47  is newer and decreases further as the secondary transfer roller  47  is used more. Therefore, the newer the secondary transfer roller  47 , the more likely it is that the pressure contact part  57 A will be contaminated by the bleed. Therefore, in a case in which the secondary transfer roller  47  has a certain number of pieces of processing, processing for removing the bleed (hereinbelow referred to as removal processing) may not be performed. The number of pieces of processing of the secondary transfer roller  47  is the total number of recording media that have passed between the secondary transfer roller  47  and the intermediate transfer belt  57 , for example. 
       FIG. 16  is a table illustrating the relationship between the number of pieces of processing of the secondary transfer roller and the removal processing according to a third modification example. Referring to  FIG. 16 , in a case in which the number of pieces of processing of the secondary transfer roller  47  is smaller than a predetermined processing threshold value (10000 in the present example), the removal processing is executed. On the other hand, in a case in which the number of pieces of processing of the secondary transfer roller  47  is equal to or larger than the processing threshold value, the removal processing is not executed. The table in  FIG. 16  is stored in the HDD  115 , for example. In the present example, although the processing threshold value is 10000, other values may be used. The processing threshold value is a value obtained by experiments in consideration of the influence of the number of pieces of processing of the secondary transfer roller  47  on the image quality. 
       FIG. 17  is a diagram illustrating an example of the functions of the CPU in the MFP according to the third modification example Referring to  FIG. 17 , the difference from the functions illustrated in  FIG. 10  is that the CPU  111  further includes an execution determination unit  270 . Since the other functions are equal to those illustrated in  FIG. 10 , the description thereof will not be repeated here. The execution determination unit  270  determines whether or not to execute the removal processing based on the current number of pieces of processing of the secondary transfer roller  47  and the table in  FIG. 16  in response to the print reception unit  210  receiving the instruction to execute print. In a case in which it is determined by the execution determination unit  270  that the removal processing is to be executed, the region specifying unit  221  of the pattern forming unit  220  performs a similar operation to that of the region specifying unit  221  in  FIG. 10 . In a case in which it is determined by the execution determination unit  270  that the removal processing is not to be executed, the print execution unit  260  executes print on the recording medium. 
       FIG. 18  is a flowchart illustrating an example of a flow of print processing according to the third modification example. The print processing in  FIG. 18  is similar to the print processing in  FIG. 11  except that step S 13  is added. Since the other steps are equal to those illustrated in  FIG. 11 , the description thereof will not be repeated here. The print processing in the present example may be combined with the print processing according to the first or second modification example. 
     In a case of YES in step S 01 , the processing proceeds to step S 13  instead of step S 02 . In step S 13 , it is determined whether or not the number of pieces of processing of the secondary transfer roller  47  is smaller than the processing threshold value. In a case in which the number of pieces of processing of the secondary transfer roller  47  is smaller than the processing threshold value, the processing proceeds to step S 02 , and otherwise, the processing proceeds to step S 12 . 
     In this case, print is executed without execution of the removal processing in steps S 02  to S 11 . As a result, delay in image formation on the recording medium and a decrease in productivity can be prevented, and the printing processing can be executed at high speed. Also, since it is not necessary to form the image pattern GP, the toner consumption can be reduced. 
     Fourth Modification Example 
     The longer the operation stop time of the intermediate transfer belt  57 , the more likely it is that the pressure contact part  57 A is contaminated by the bleed. Therefore, in a case in which the operation stop time of the intermediate transfer belt  57  is short, the contamination of the pressure contact part  57 A by the bleed has a small effect on the image quality of the image formed on the recording medium, and thus the removal processing does not have to be performed. 
       FIG. 19  is a table illustrating the relationship between the operation stop time of the intermediate transfer belt and the removal processing in a fourth modification example. Referring to  FIG. 19 , in a case in which the operation stop time of the intermediate transfer belt  57  is shorter than a predetermined time threshold value (72 hours in the present example), the removal processing is not executed. On the other hand, in a case in which the operation stop time of the intermediate transfer belt  57  is equal to or longer than the time threshold value, the removal processing is executed. The table in  FIG. 19  is stored in the HDD  115 , for example. In the present example, although the time threshold value is 72 hours, other values may be used. The time threshold value is a value obtained by experiments in consideration of the influence of the operation stop time of the intermediate transfer belt  57  (the pressure contact time between the intermediate transfer belt  57  and the secondary transfer roller  47 ) on the image quality. 
     The function of the HDD  115  in the MFP  100  in the present modification example is similar to the function of the HDD  115  in the MFP  100  in the third modification example in  FIG. 17 . The execution determination unit  270  in the present example determines whether or not to execute the removal processing based on the operation stop time of the intermediate transfer belt  57  and the table in  FIG. 19 . In a case in which it is determined by the execution determination unit  270  that the removal processing is to be executed, the region specifying unit  221  performs a similar operation to that of the region specifying unit  221  in  FIG. 10 . In a case in which it is determined by the execution determination unit  270  that the removal processing is not to be executed, the print execution unit  260  executes print on the recording medium. 
       FIG. 20  is a flowchart illustrating an example of a flow of print processing according to the fourth modification example. The print processing in  FIG. 20  is similar to the print processing in  FIG. 18  except that step S 13  is changed to step S 13 A. Since the other steps are equal to those illustrated in  FIG. 18 , the description thereof will not be repeated here. The print processing in the present example may be combined with the print processing according to the first to third modification examples. 
     In a case of YES in step S 01 , the processing proceeds to step S 13 A instead of step S 02 . In step S 13 A, it is determined whether or not the operation stop time of the intermediate transfer belt  57  is equal to or longer than the time threshold value. In a case in which the operation stop time of the intermediate transfer belt  57  is equal to or longer than the time threshold value, the processing proceeds to step S 02 , and otherwise, the processing proceeds to step S 12 . 
     In this case, print is executed without execution of the removal processing in steps S 02  to S 11 . As a result, delay in image formation on the recording medium and a decrease in productivity can be prevented, and the printing processing can be executed at high speed. Also, since it is not necessary to form the image pattern GP, the toner consumption can be reduced. 
     As described above, the print processing according to the present example may be combined with the print processing according to the third modification example. Here, even in a case in which the secondary transfer roller  47  is new, and in a case in which the operation stop time of the intermediate transfer belt  57  is short, there is a case in which the contamination of the pressure contact part  57 A by the bleed has a small effect on the image quality of the image formed on the recording medium. On the other hand, even in a case in which the secondary transfer roller  47  is old, and in a case in which the operation stop time of the intermediate transfer belt  57  is long, there is a case in which the contamination of the pressure contact part  57 A by the bleed has a large effect on the image quality of the image formed on the recording medium. Therefore, in a case in which the print processing according to the third modification example and the print processing according to the fourth modification example are combined, whether or not the removal processing is executed is determined in accordance with the combination of the number of pieces of processing of the secondary transfer roller  47  with the operation stop time of the intermediate transfer belt  57 . 
       FIG. 21  is a table illustrating the relationship among the number of pieces of processing of the secondary transfer roller, the operation stop time of the intermediate transfer belt, and the removal processing. Referring to  FIG. 21 , in a case in which the number of pieces of processing of the secondary transfer roller  47  is smaller than a predetermined processing threshold value (10000 in the present example), and in which the operation stop time of the intermediate transfer belt  57  is shorter than a predetermined first time threshold value (72 hours in the present example), the removal processing is not executed. In a case in which the number of pieces of processing of the secondary transfer roller  47  is smaller than the processing threshold value, and in which the operation stop time of the intermediate transfer belt  57  is equal to or longer than the first time threshold value, the removal processing is executed. 
     In a case in which the number of pieces of processing of the secondary transfer roller  47  is equal to or larger than the processing threshold value, and in which the operation stop time of the intermediate transfer belt  57  is shorter than a predetermined second time threshold value (168 hours in the present example), the removal processing is not executed. In a case in which the number of pieces of processing of the secondary transfer roller  47  is equal to or larger than the processing threshold value, and in which the operation stop time of the intermediate transfer belt  57  is equal to or longer than the second time threshold value, the removal processing is executed. In the example in  FIG. 21 , although the processing threshold value is 10000, the first time threshold value is 72 hours, and the second time threshold value is 168 hours, these threshold values may be other values. The execution determination unit  270  determines whether or not to execute the removal processing based on the current number of pieces of processing of the secondary transfer roller  47 , the current operation stop time of the intermediate transfer belt  57 , and the table in  FIG. 21 . 
     As described above, the MFP  100  according to the first embodiment functions as an image forming apparatus, the intermediate transfer belt  57  and the secondary transfer roller  47  are in pressure contact with each other, and the cleaning blade  59  is in contact with the intermediate transfer belt  57  to remove toner remaining on the intermediate transfer belt  57 . In the MFP  100 , an image pattern GP is formed in a region including at least a part of the pressure contact part  57 A that is in pressure contact with the secondary transfer roller  47  when the operation of the intermediate transfer belt  57  is stopped, density of the image pattern GP is acquired, driving time of the intermediate transfer belt  57  is adjusted based on the density of the image pattern, and the intermediate transfer belt  57  is driven for the driving time adjusted at a stage before an image is formed on a recording medium. Therefore, since the density of the image pattern in the pressure contact part  57 A differs depending on the degree of contamination of the pressure contact part  57 A of the intermediate transfer belt  57  due to bleed of the secondary transfer roller  47 , the driving time of the intermediate transfer belt  57  is adjusted in accordance with the degree of contamination of the pressure contact part  57 A. Therefore, foreign matters including bleed adhering to the pressure contact part  57 A are removed by the cleaning blade  59 . This can prevent the quality of the image formed on the recording medium from being lowered. 
     Preferably, the image pattern GP is formed in a region including at least the part of the pressure contact part  57 A and at least a part of the non-pressure contact part  57 B, and the driving time of the intermediate transfer belt  57  is adjusted based on distribution of the density of the image pattern GP acquired. Therefore, the degree of contamination of the pressure contact part  57 A can be detected easily. 
     Preferably, a density difference between the image pattern GP formed in at least the part of the pressure contact part  57 A and the image pattern GP formed in at least the part of the non-pressure contact part  57 B of the intermediate transfer belt  57  is acquired as the distribution of the density of the image pattern GP. Therefore, the degree of contamination of the pressure contact part  57 A can be detected accurately. 
     Preferably, a density difference between a maximum density value and a minimum density value in the image pattern GP is acquired as the distribution of the density of the image pattern GP. Therefore, the degree of contamination of the pressure contact part  57 A can be detected easily. 
     Preferably, the image pattern GP is formed in at least the part of the pressure contact part  57 A and at least the part of the non-pressure contact part  57 B so as to bridge over the pressure contact part  57 A in a front-rear direction in a driving direction of the intermediate transfer belt  57 . Therefore, the density difference of the image pattern GP can be obtained more easily since, in a case in which the pressure contact part  57 A is contaminated, the density of the image pattern GP in the pressure contact part  57 A and that in the non-pressure contact part  57 B located at the front and rear of the pressure contact part  57 A differ significantly. 
     Preferably, the image pattern GP is formed in a region in which at least the part of the pressure contact part  57 A and at least the part of the non-pressure contact part  57 B are continuous. Therefore, the density difference of the image pattern GP can be obtained more easily since, in a case in which the pressure contact part  57 A is contaminated, the density of the image pattern GP differs significantly at a boundary portion between the pressure contact part  57 A and the non-pressure contact part  57 B. 
     Preferably, the driving time of the intermediate transfer belt  57  is extended so that the driving time is longer as the density difference is higher. Therefore, since the driving time is determined in accordance with the degree of contamination of the pressure contact part  57 A of the intermediate transfer belt  57 , foreign matters can efficiently be removed from the intermediate transfer belt  57 . 
     Preferably, after driving of the intermediate transfer belt  57  is executed, operation is repeated until the density difference is equal to or lower than a predetermined allowable value. Therefore, foreign matters adhering to the pressure contact part  57 A can be removed reliably. 
     Preferably, the image pattern GP is formed in a case in which the number of pieces of processing of the secondary transfer roller  47  is equal to or smaller than a predetermined value. Therefore, in a case in which the number of pieces of processing of the secondary transfer roller  47  exceeds the predetermined value, it is considered that the contamination of the pressure contact part  57 A of the intermediate transfer belt  57  has a small effect on the image quality of the image formed on the recording medium, and a series of operations to remove foreign matters in the pressure contact part  57 A is not performed. In this case, since the intermediate transfer belt  57  is not driven, delay in image formation on the recording medium and a decrease in productivity can be prevented. 
     Preferably, the image pattern GP is formed in a case in which operation stop time of the intermediate transfer belt  57  is equal to or longer than a predetermined value. Therefore, in a case in which the operation stop time of the intermediate transfer belt  57  is shorter than the predetermined value, it is considered that the contamination of the pressure contact part  57 A of the intermediate transfer belt  57  has a small effect on the image quality of the image formed on the recording medium, and a series of operations to remove foreign matters in the pressure contact part  57 A is not performed. In this case, since the intermediate transfer belt  57  is not driven, delay in image formation on the recording medium and a decrease in productivity can be prevented. 
     Second Embodiment 
     The appearance of the MFP  100  according to a second embodiment is the same as that illustrated in  FIG. 1 . Also, the hardware configuration of the MFP  100  according to the second embodiment is the same as that illustrated in  FIG. 2 .  FIG. 22  is a diagram illustrating an example of the functions of the CPU in the MFP according to the second embodiment. Referring to  FIG. 22 , the difference from the functions illustrated in  FIG. 10  is that the CPU  111  further includes a density prediction unit  280  and that the density acquisition unit  230  does not include the non-pressure contact density detection unit  234 . Since the other functions are equal to those illustrated in  FIG. 10 , the description thereof will not be repeated here. 
     The region specifying unit  221  specifies a region in the pressure contact part  57 A in which the image pattern GP is to be formed in response to the print reception unit  210  receiving an instruction to execute print. In this case, an image pattern GP having predetermined density is formed in the region including at least a part of the pressure contact part  57 A specified by the region specifying unit  221 . 
     The density prediction unit  280  acquires as predicted density the density of an image pattern GP formed on the intermediate transfer belt  57  by the pattern forming unit  220  in a state in which the intermediate transfer belt  57  is not contaminated. The predicted density may be obtained by an arithmetic expression using a control value obtained by image stabilization processing. Also, in consideration of deterioration of the image former  140  with time, the predicted density may be a value measured with respect to the cumulative driving time of the image former  140  by experiments or the like. The density difference calculation unit  235  calculates a difference between the density detected by the pressure contact density detection unit  233  and the predicted density acquired by the density prediction unit  280 . As a result, the density difference ΔE of the image pattern GP is acquired. In this case, the driving time of the intermediate transfer belt  57  is adjusted by the driving time adjustment unit  240  based on the density difference ΔE of the image pattern GP. 
       FIG. 23  is a flowchart illustrating an example of a flow of print processing according to the second embodiment. The print processing in  FIG. 23  is similar to the print processing in  FIG. 11  except that step S 02  is changed to step S 02 A, step S 06  is changed to step S 06 A, and step S 07  is changed to steps S 07 A. Since the other steps are equal to those illustrated in  FIG. 11 , the description thereof will not be repeated here. Note that the first to fourth modification examples of the first embodiment can also be applied to the printing processing illustrated in  FIG. 23 . 
     In step S 02 A, a region including at least a part of the pressure contact part  57 A of the intermediate transfer belt  57  is specified as a region in which the image pattern GP is to be formed, and the processing proceeds to step S 03 . In step S 06 A, predetermined density of the image pattern GP is acquired as predicted density, and the processing proceeds to step S 07 A. In step S 07 A, a difference between the density of the image pattern GP in the pressure contact part  57 A and the predicted density is calculated as the density difference ΔE of the image pattern GP, and the processing proceeds to step S 08 . 
     According to the present embodiment, contamination of the pressure contact part  57 A by bleed can be detected without forming an image pattern GP in the non-pressure contact part  57 B. Therefore, the amount of toner consumed for forming the image pattern GP can be reduced. 
     In the MFP  100  according to the second embodiment, density of an image pattern GP formed on the intermediate transfer belt  57  is predicted, and based on a density difference between the density of the image pattern GP predicted and the density of the image pattern GP acquired, driving time of an image carrier is adjusted. Therefore, since the image pattern GP is formed in the pressure contact part  57 A of the intermediate transfer belt  57 , the amount of toner consumed for forming the image pattern GP can be reduced. 
     Other Embodiments 
     In the first or second embodiment, the image former  140  employs an intermediate transfer method and may employ a direct transfer method. Further, although the image carrier is the intermediate transfer belt  57 , and the elastic body is the secondary transfer roller  47 , each of the embodiments is not limited to this. The elastic body may be the cleaning blade  59 . Alternatively, the image carrier may be the photoconductor drums  53 Y,  53 M,  53 C, and  53 K. In this case, the elastic body may be the charging rollers  54 Y,  54 M,  54 C, and  54 K. Alternatively, in a case in which the image former  140  employs the direct transfer method, the elastic body may be the transfer rollers that are in pressure contact with the photoconductor drums. 
     APPENDIX 
     Preferably, the image forming apparatus further includes a first image carrier (photoconductor drum) that carries a toner image formed by toner, and a second image carrier (intermediate transfer belt) to which the toner image carried on the first image carrier is transferred and that carries the toner image transferred, in which the elastic body transfers the toner image carried on the second image carrier to a recording medium. 
     Preferably, the image carrier carries the toner image formed by toner, the elastic body causes the image carrier to be charged, and the image carrier carries the toner image as an electrostatic latent image formed as the image carrier is exposed after being charged is developed. 
     Although embodiments of the present disclosure have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present disclosure should be interpreted by terms of the appended claims rather than by terms of the above description, and it is intended that all modifications are included within the meaning and scope equivalent to the patent claims. 
     As used herein, the words “can” and “may” are used in a permissive (i.e., meaning having the potential to), rather than mandatory sense (i.e., meaning must). The words “include,” “includes,” “including,” and the like mean including, but not limited to. Similarly, the singular form of “a” and “the” include plural references unless the context clearly dictates otherwise. And the term “number” shall mean one or an integer greater than one (i.e., a plurality).