Patent Publication Number: US-11022916-B2

Title: Image forming apparatus, recording medium. and control method for reducing pressure gradient between rollers

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Japanese patent application No. 2019-079537 filed on Apr. 18, 2019, including description, claims, drawings, and abstract the entire disclosure is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technological Field 
     The present invention relates to an image forming apparatus, a recording medium storing a control program for the image forming apparatus, and a control method for the image forming apparatus. 
     2. Description of the Related Art 
     The image forming apparatus is provided with a roller pair for performing sheet conveyance and image formation. It is desirable that in two rollers of the roller pair, the pressure between the rollers at the time of pressing is uniform in the axial direction of the rollers, and if the pressure is not uniform, a problem such as a paper jam or poor quality of the printed matter is caused. Such a problem becomes noticeable when the basis weight of the sheet is relatively large or conversely when the basis weight is relatively small. Also, the higher the printing speed, the more noticeable. 
     However, due to machine tolerance, a pressure gradient may occur in which the pressure between the rollers inclines in the axial direction of the rollers due to a positional deviation of the roller shaft of the roller pair in a pressing direction or the like. 
     As a prior art for detecting such a pressure gradient, the following technology is described in Unexamined Japanese Patent Publication No. 2012-47810. By pressing a transfer roll on a photosensitive drum of a toner transfer source via an intermediate transfer belt of a toner transfer destination, a toner is transferred to the intermediate transfer belt. Then, the gradient of pressing force in the axial direction of the transfer roll is detected by detecting, with an optical sensor, the density difference of the toner transferred to the intermediate transfer belt at a plurality of different positions in the axial direction of the transfer roll. Further, the following technology is described in Unexamined Japanese Patent Publication No. 2008-287137. After the toner on the intermediate transfer body is transferred to a sheet at the nip formed by bringing the transfer member into contact with the intermediate transfer body, the residual toner densities at two locations near both axial ends on the intermediate transfer body are detected with the optical sensor. If any of the toner densities is higher than a threshold value, it is determined that a contact failure has occurred. 
     SUMMARY 
     However, the above-described prior art has a problem that even when the cause of the difference in toner density in the axial direction between the rollers or the like is not the pressure gradient in the axial direction between the rollers, it is determined that the pressure gradient is the cause. In this case, even when the pressure gradient is corrected, problems such as a difference in toner density cannot be solved. In addition, since the pressure gradient in the axial direction between the rollers cannot be detected unless the toner is actually transferred, there is a problem that the operation is complicated. Further, there is a problem that it is impossible to cope with a case where the influence of the pressure gradient in the axial direction between the rollers occurs only in the conveyance of the sheet such as a paper jam. 
     The present invention has been made to solve such a problem. That is, an object of the present invention is to provide an image forming apparatus a recording medium storing a control program for the image forming apparatus, and a control method for the image forming apparatus, which can easily and accurately reduce the pressure gradient in the axial direction between rollers, a recording medium storing a control program for the image forming apparatus, and a control method for the image forming apparatus. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present invention, the image forming apparatus, the recording medium storing the control program for the image forming apparatus, and the control method for the image forming apparatus reflecting one aspect of the present invention comprises the following. 
     An image forming apparatus comprising: a driver that presses and separates two rollers via a belt; a detector that detects a position of said belt in an axial direction of one roller of said two rollers; and a hardware processor that calculates, based on a detection result by said detector, a first movement amount of the position of said belt in said axial direction at time of traveling of said belt in a state where said two rollers are separated and a second movement amount of the position of said belt in said axial direction at the time of traveling of said belt in a state where said two rollers are pressed. 
     A non-transitory computer-readable storage medium storing a control program for an image forming apparatus which includes a driver that presses and separates two rollers via a belt and a detector that detects a position of said belt in an axial direction of one roller of said two rollers, the control program causing a computer to perform: a process having a procedure of calculating, based on a detection result by said detector, a first movement amount of the position of said belt in said axial direction when said belt is made to travel for a predetermined time in a state where said two rollers are separated and a second movement amount of the position of said belt in said axial direction when said belt is made to travel for said predetermined time in a state where said two rollers are pressed. 
     A control method of an image forming apparatus which includes a driver that presses and separates two rollers via a belt and a detector that detects a position of said belt in an axial direction of one roller of said two rollers, the method comprising: calculating, based on a detection result by said detector, a first movement amount of the position of said belt in said axial direction when said belt is made to travel for a predetermined time in a state where said two rollers are separated and a second movement amount of the position of said belt in said axial direction when said belt is made to travel for said predetermined time in a state where said two rollers are pressed. 
     The objects, features, and characteristics of this invention other than those set forth above will become apparent from the description given herein below with reference to preferred embodiments illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention. 
         FIG. 1  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 2  is a block diagram illustrating the configuration of the image forming apparatus; 
         FIGS. 3A and 3B  are explanatory diagrams illustrating a state in which a secondary transfer roller and an opposing roller are separated and pressed; 
         FIGS. 4A to 4C  are explanatory diagrams illustrating examples of a push-up amount of a spring-included sheet metal by a cam due to rotation of the cam; 
         FIG. 5  is an explanatory diagram illustrating an operation of a roller position adjuster when parallelism between rollers is adjusted by the roller position adjuster; 
         FIG. 6  is a diagram illustrating an effect on a belt movement amount by a pressure gradient at the time of pressing a target roller pair that can be separated via the belt and an effect on the belt movement amount by rollers other than the target roller pair about each of the time of separation and the time of pressing the target roller pair; 
         FIG. 7  is a diagram illustrating a relation between a difference between a first movement amount and a second movement amount, and the parallelism between rollers and the pressure gradient between rollers; 
         FIG. 8  is a flowchart illustrating an operation of the image forming apparatus; 
         FIG. 9  is an explanatory diagram illustrating the operation of the roller position adjuster when the parallelism between rollers is adjusted by the roller position adjuster; 
         FIGS. 10A to 10D  are explanatory diagrams illustrating examples of shapes of two cams when viewed from a direction of a rotation shaft; and 
         FIG. 11  is an explanatory diagram illustrating a configuration of a photosensitive drum and a transfer roller of an imaging device of the image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. 
     An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. Note that, in the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of description, and may be different from the actual ratios. 
     First Embodiment 
       FIG. 1  is a schematic diagram illustrating a configuration of an image forming apparatus  100 .  FIG. 2  is a block diagram illustrating the configuration of the image forming apparatus  100 . Here, in this embodiment, as an example, a secondary transfer roller  431 , an opposing roller  44 , and an intermediate transfer belt  42  in a secondary transferor are described as corresponding to two rollers that are separated (pressed/separated) via a belt, and the belt, respectively. However, the present invention is not limited to this, and may be applied to other roller and belt configurations as in the third to fifth embodiments described below. 
     The image forming apparatus  100  includes a controller  110 , a storage  120 , a communicator  130 , an operation display  140 , an image reader  150 , an image controller  160 , and an image former  170 . These components are communicably connected to each other by a bus  180 . The image forming apparatus  100  can be configured by, for example, an MFP (MultiFunction Peripheral). 
     The controller  110  includes a CPU (Central Processing Unit) and various memories, and controls the above units and performs various arithmetic processes according to a program. The controller  110  configures an arithmetic controller. Details of the operation of the controller  110  will be described later. 
     The storage  120  is configured by an SDD (Solid State Drive), an HDD (Hard Disc Drive) or the like, and stores various programs and various data. 
     The communicator  130  is an interface for performing communication between the image forming apparatus  100  and an external device. As the communicator  130 , a network interface based on standards such as Ethernet (registered trademark), SATA, and IEEE1394 is used. Further, as the communicator  130 , various local connection interfaces such as Bluetooth (registered trademark) and a wireless communication interface such as IEEE802.11 or the like are used. The communicator  130  configures an outputter. 
     The operation display  140  includes a touch panel, numeric keys, a start button, a stop button, and the like, and is used for displaying various pieces of information and inputting various instructions. The operation display  140  forms a display and an adjustment mechanism. Further, the operation display forms an outputter instead of the communicator  130 . 
     The image reader  150  has a light source such as a fluorescent lamp and an imaging element such as a CCD (Charge Coupled Device) image sensor. The image reader  150  emits light from a light source to a document set at a predetermined reading position, photoelectrically converts the reflected light thereof with the imaging element, and generates image data from the electric signal thereof. 
     The image controller  160  performs layout processing and rasterization processing of print data included in a print job or the like received by the communicator  130 , and generates bitmap image data. 
     The print job is a general term for a print command for the image forming apparatus  100 , and includes print data and print settings. The print data is data of the document to be printed, and the print data may include various data such as image data, vector data, and text data, for example. Specifically, the print data may be PDL (Page Description Language) data, PDF (Portable Document Format) data, or TIFF (Tagged Image File Format) data. The print settings are settings related to image formation on a sheet  900 , and include various settings such as the number of pages, the number of copies, the sheet type, selection of color or monochrome, and page layout. 
     The image former  170  includes an imaging device  40 , a fixer  50 , a sheet feeding unit  60 , a sheet conveying unit  70 , a roller position adjuster  80 , and a belt position detector  81 . The roller position adjuster  80  configures a driver. The belt position detector  81  configures a detector. 
     The image forming device  40  includes imaging units  41 Y,  41 M,  41 C, and  41 K corresponding to toners of colors of Y (yellow), M (magenta), C (cyan), and K (black). A toner image is formed on a photosensitive drum  47  by the imaging units  41 Y,  41 M,  41 C, and  41 K through charging, exposure, and development processes based on the image data. The exposure is performed by scanning the photosensitive drum  47  with a laser beam. When the photosensitive drum  47  and a primary transfer roller  48  are pressed via the intermediate transfer belt  42 , and the intermediate transfer belt  42  travels to be rotated by the driving force of a driving roller  45 , the toner images formed on the photosensitive drums  47  as an image carrier are superposed on the intermediate transfer belt  42  in order, thereby forming a color toner image. The intermediate transfer belt  42  travels in the sub-scanning direction (the direction of the straight arrow). When the secondary transfer roller  431  and the opposing roller  44  are pressed via the intermediate transfer belt  42 , the color toner image formed on the intermediate transfer belt  42  is transferred onto the conveyed sheet  900 . The width of the intermediate transfer belt  42  is, for example, 500 mm. The sliding speed of the intermediate transfer belt  42  is, for example, 500 mm/s. 
     A steering roller  46  changes the tension applied to the intermediate transfer belt  42  by adjusting the steering angle, and adjusts the position of the intermediate transfer belt  42  in the width direction with respect to the opposing roller  44  or the like that stretches the intermediate transfer belt  42 . Accordingly, the position of the intermediate transfer belt  42  in the width direction with respect to the opposing roller  44  or the like is held substantially at the axial center of the opposing roller  44  or the like, thereby the intermediate transfer belt  42  is prevented from moving in the width direction and dropping from the opposing roller  44  or the like, or the like. The steering roller  46  configures a steering mechanism. 
       FIGS. 3A and 3B  are explanatory diagrams illustrating a state where the secondary transfer roller  431  and the opposing roller  44  are separated and pressed.  FIG. 3A  illustrates a state where the secondary transfer roller  431  and the opposing roller  44  are separated.  FIG. 3B  illustrates a state where the secondary transfer roller  431  and the opposing roller  44  are pressed. 
     An endless belt  432  is stretched on the secondary transfer roller  431  together with a plurality of other rollers. The secondary transfer roller  431 , and a plurality of other rollers stretching the belt  432  together with the secondary transfer roller  431 , and the endless belt  432  are included in a housing that can be inserted into and removed from the image forming apparatus  100 , thereby configuring a secondary transferor  43 . The secondary transferor  43  becomes a component of the image forming apparatus  100  by being inserted into the image forming apparatus  100 . 
     The secondary transfer roller  431 , and the plurality of other rollers stretching the belt  432  together with the secondary transfer roller  431 , and the endless belt  432  need not be included in the housing, thereby being a component installed as a part of the image forming apparatus  100 . Further, in the secondary transferor  43 , the endless belt  432  need not be used. In this case, the plurality of other rollers stretching the belt  432  together with the secondary transfer roller  431  are not required. 
     The roller position adjuster  80  includes a cam  82 , a spring-included sheet metal  83 , and a drive motor  84  (see  FIG. 5 ). The drive motor  84  configures a drive source. As the drive motor  84 , for example, a stepping motor can be used. The cam  82  configures a conversion mechanism. The spring-included sheet metal  83  and the cam  82  are provided at positions corresponding to both ends of the secondary transfer roller  431 , respectively. The roller position adjuster  80  adjusts the position of the secondary transfer roller  431  in the pressing direction (hereinafter, also simply referred to as “pressing direction”) to the opposing roller  44 . The roller position adjuster  80  adjusts the position of the secondary transfer roller  431  in the pressing direction so as to press the secondary transfer roller  431  with the opposing roller  44  and to adjust the parallelism (hereinafter, also simply referred to as “parallelism between rollers”) of the secondary transfer roller  431  with respect to the opposing roller  44 . The parallelism between the rollers is the difference in the distance between both ends of one roller and the other roller. The parallelism between the rollers may be, for example, the parallelism between the secondary transfer roller  431  and the opposing roller  44  when the secondary transfer roller  431  and the opposing roller  44  are pressed. 
     The secondary transfer roller  431  is pressed against the opposing roller  44  by being urged toward the opposing roller  44  by the roller position adjuster  80 . Specifically, in a state where a shaft  431   a  of the secondary transfer roller  431  is in contact with the spring of the spring-included sheet metal  83 , the bottom surface of the spring-included sheet metal  83  is pushed up by the cam  82  abutting on the bottom surface when the cam  82  rotates about a rotation shaft  82   a  attached to the eccentric position. As a result, the secondary transfer roller  431  is urged toward the opposing roller  44  together with the spring-included sheet metal  83 , so that the secondary transfer roller  431  is pressed against the opposing roller  44 . The secondary transfer roller  431  may be in contact with the spring of the spring-included sheet metal  83  via a bearing such as a ball bearing provided on the shaft  431   a  of the secondary transfer roller  431 . The diameter of each of the secondary transfer roller  431  and the opposing roller  44  is, for example, 10 mm. The secondary transfer roller  431  and the opposing roller  44  are pressed such that the total load in the axial direction (hereinafter, also referred to as “roller axial direction”) of the opposing roller  44  (or the secondary transfer roller  431 ) is, for example, between 70 N to 130 N. Hereinafter, a state in which the secondary transfer roller  431  and the opposing roller  44  are pressed is also simply referred to as “the time of pressing”. A state in which the secondary transfer roller  431  and the opposing roller  44  are separated is also simply referred to as “the time of separation”. 
       FIGS. 4A to 4C  are explanatory diagrams illustrating an example of the push-up amount of the spring-included sheet metal  83  by the cam  82  due to the rotation of the cam  82 . In  FIGS. 4A to 4C , the straight arrows indicate the pressing direction. The arc arrows indicate the rotation direction of the cam  82 . 
       FIGS. 4A to 4C  illustrate the rotation state of the cam  82  and the position of the spring-included sheet metal  83  in the pressing direction due to the rotation of the cam  82  when the push-up amounts of the spring-included sheet metal  83  are 0 mm, 1.5 mm, and 3 mm, respectively. 
       FIG. 5  is an explanatory diagram illustrating the operation of the roller position adjuster  80  when the parallelism between the rollers is adjusted by the roller position adjuster  80 . 
     As described above, the spring-included sheet metal  83  and the cam  82  are installed at positions corresponding to both ends of the secondary transfer roller  431 , respectively. The drive motor  84  for rotating and driving the rotation shaft  82   a  of the cam  82  is provided corresponding to each cam  82 . The roller position adjuster  80  adjusts the positions of the both ends of the secondary transfer roller  431  in the pressing direction (the direction of the arrow) by adjusting the push-up amount of each spring-included sheet metal  83  by the rotation of each cam  82 . Thereby, the parallelism between the rollers is adjusted, and the gradient of the pressure at the time of pressing between the secondary transfer roller  431  and the opposing roller  44  (hereinafter, also referred to as “pressure gradient between the rollers”) is adjusted. 
     The belt position detector  81  detects the position of the intermediate transfer belt  42  in the roller axial direction (hereinafter, also simply referred to as “the position of the intermediate transfer belt  42 ”). The position of the intermediate transfer belt  42  can be detected, for example, as the position of the end of the intermediate transfer belt  42  in the width direction (the axial direction of the opposing roller  44 ) in the axial direction of the opposing roller  44 . The belt position detecting unit  81  is configured by, for example, a line sensor arranged along the width direction of the intermediate transfer belt  42 , and the position (the end position or the like) of the intermediate transfer belt  42  is detected based on the light reflectance, which is measured by the line sensor, by the opposing roller  44  and the intermediate transfer belt  42 . 
     Returning to  FIG. 1 , the description will be continued. 
     The fixer  50  includes a fixing roller  51   a , a fixing belt  51   b , a heating roller  51   c , and a pressure roller  52 . When the fixing roller  51   a  and the pressure roller  52  are pressed against each other via the endless fixing belt  51   b , a fixing nip is formed between the fixing belt  51   b  and the pressure roller  52 . The fixing belt  51   b  is stretched by the fixing roller  51   a  and the heating roller  51   c . The fixing roller  51   a  and the pressure roller  52  are individually driven to rotate by drive motors (not illustrated). The fixing belt  51   b  and the heating roller  51   c  rotate following the rotation of the fixing roller  51   a . The heating roller  51   c  and the pressure roller  52  are each heated to a predetermined temperature by a built-in heater. The fixing belt  51   b  is heated by the heating roller  51   c  to stretch. The sheet  900  conveyed to the fixer  50  is heated and pressed by the fixing nip such that the toner image is fixed (melt-fixed), and is conveyed by the rotation of the fixing belt  51   b  and the pressure roller  52 . 
     The sheet  900  on which the toner image is fixed by the fixer  50  is discharged to the discharge tray  90  as a printed matter. 
     The sheet feeding unit  60  has a plurality of sheet feeding trays  61  and  62 , and feeds out the sheets  900  stored in the sheet feeding trays  61  and  62  one by one to a downstream conveyance path. 
     The sheet conveying unit  70  has a plurality of conveying rollers for conveying the sheet  900 , and conveys the sheet  900  between the image forming device  40 , the fixer  50 , and the sheet feeding unit  60 . The plurality of conveying rollers include a registration roller  71  for correcting the gradient of the sheet  900  and a loop roller  72  for forming a predetermined amount of loop on the sheet  900 . 
     The sheet conveying unit  70  discharges the sheet  900  on which the image is formed to the discharge tray  90 . 
     The operation of the controller  110  will be described in detail. 
     Based on the detection result of the position of the intermediate transfer belt  42  detected by the belt position detecting unit  81 , the controller  110  calculates the movement amount of the intermediate transfer belt  42  in the roller axial direction when the intermediate transfer belt  42  is made to travel for a predetermined time (hereinafter, also referred to as “belt movement amount”). The controller  110  calculates a first movement amount that is a belt movement amount in a state where the secondary transfer roller  431  and the opposing roller  44  are separated by the roller position adjuster  80 . The controller  110  calculates a second movement amount that is a belt movement amount in a state where the secondary transfer roller  431  and the opposing roller  44  are pressed by the roller position adjuster  80 . The predetermined time is, for example, one second, but is not limited thereto, and may be any time between 0.5 seconds and 10 seconds. Note that, for example, the movement amount of the intermediate transfer belt  42  in the roller axial direction when the intermediate transfer belt  42  travels for five seconds may be measured to calculate the movement amount of the intermediate transfer belt  42  in the roller axial direction per second and use the amount as a belt movement amount. In addition, the belt movement amount may be a movement amount of the intermediate transfer belt  42  in the roller axial direction when the intermediate transfer belt  42  travels a predetermined distance. The controller  110  further calculates a difference between the first movement amount and the second movement amount. 
       FIG. 6  is a diagram illustrating an effect on the belt movement amount by the pressure gradient at the time of pressing a target roller pair that can be separated via the belt and an effect on the belt movement amount by rollers other than the target roller pair about each of the time of separation and the time of pressing the target roller pair. The target roller pair corresponds to the secondary transfer roller  431  and the opposing roller  44 . The rollers other than the target roller pair correspond to the driving roller  45  and the like that stretches the intermediate transfer belt  42 . The belt movement amount at the time of separation of the target roller pair corresponds to the first movement amount. The belt movement amount at the time of pressing the target roller pair corresponds to the second movement amount. 
     As illustrated in  FIG. 6 , when the target roller pair is separated, the rollers other than the target roller pair affect the belt movement amount, and the pressure gradient at the time of pressing the target roller pair does not affect the belt movement amount. The reason why the pressure gradient at the time of pressing the target roller pair does not affect the belt movement amount is that no pressure is generated between the rollers of the target roller pair at the time of separation of the target roller pair. When the target roller pair is pressed, the rollers other than the target roller pair affect the belt movement amount, and the pressure gradient at the time of pressing the target roller pair also affects the belt movement amount. The effect of the rollers other than the target roller pair on the belt movement amount is made similarly at both of the time of separation and the time of pressing of the target roller pair. Therefore, by calculating the difference between the belt movement amount (first movement amount) at the time of separation of the target roller pair and the belt movement amount (second movement amount) at the time of pressing the target roller pair, the pressure gradient at the time of pressing the target roller pair can be evaluated with high accuracy. 
     The controller  110  calculates the parallelism between the rollers and the pressure gradient between the rollers based on the first movement amount and the second movement amount. 
       FIG. 7  is a diagram illustrating a relation between the difference between the first movement amount and the second movement amount, and the parallelism between the rollers and the pressure gradient between the rollers. These relations can be obtained, for example, by experiment. The parallelism between the rollers and the pressure gradient between the rollers configure the adjustment index. In the example of  FIG. 7 , a value obtained by subtracting the first movement amount from the second movement amount is calculated as a difference between the first movement amount and the second movement amount. The parallelism between the rollers is calculated as the positional deviation of the roller shaft in the pressing direction (the difference between the shaft of the secondary transfer roller  431  and the shaft of the opposing roller  44 ) at both ends of the shaft of the secondary transfer roller  431 . Specifically, the parallelism between the rollers is calculated as a value obtained by subtracting the distance from the shaft of the opposing roller  44  at the front end of the secondary transfer roller  431  from the distance from the shaft of the opposing roller  44  at the rear end. Here, the front end of the secondary transfer roller  431  is, for example, the end closer to the insertion opening of the secondary transferor  43  inserted into the image forming apparatus  100 , and the rear end of the secondary transfer roller  431  is the end farthest from the insertion opening. The pressure gradient between the rollers is calculated as the difference of the pressure on the secondary transfer roller  431  between both ends of the secondary transfer roller  431 . Specifically, the pressure gradient between the rollers is calculated as the value obtained by subtracting the pressure applied to the secondary transfer roller  431  by the opposing roller  44  at the rear end of the secondary transfer roller  431  from the pressure applied to the secondary transfer roller  431  by the opposing roller  44  at the front end. 
     As illustrated in  FIG. 7 , for example, when the difference between the first movement amount and the second movement amount is −2 mm, the positional deviation of the roller shaft is +0.5 mm, and the pressure gradient between the rollers is +10 N. The minus sign of the value of the difference between the first movement amount and the second movement amount indicates that the intermediate transfer belt  42  moves to the rear side of the secondary transfer roller  431 . The positive sign of the value of the positional deviation of the roller shaft indicates that the distance from the shaft of the opposing roller  44  at the front end of the secondary transfer roller  431  is shorter than the distance from the shaft of the opposing roller  44  at the rear end. The positive sign of the value of the pressure gradient between the rollers indicates that the pressure on the secondary transfer roller  431  at the front end of the secondary transfer roller  431  is larger than the pressure on the secondary transfer roller  431  at the rear end. 
     As described above, the difference between the first movement amount and the second movement amount reflects the pressure gradient between the rollers at the time of pressing with high accuracy. Further, the pressure gradient between the rollers at the time of pressing is caused by the parallelism between the rollers. Therefore, the parallelism between the rollers and the pressure gradient between the rollers can be calculated based on the difference between the first movement amount and the second movement amount. For example, the relations between the difference between the first movement amount and the second movement amount, and the parallelism between the rollers and the pressure gradient between the rollers are each measured by experiments or the like, and an approximate expression indicating the relations is obtained in advance. Then, using the relational expression, the parallelism between the rollers and the pressure gradient between the rollers can be calculated from the measurement result of the difference between the first movement amount and the second movement amount. 
     The controller  110  calculates the first movement amount, the second movement amount, and the difference between the first movement amount and the second movement amount at at least one timing of the time of replacement of members configuring the image forming apparatus  100 , the time of shipment of the image forming apparatus  100 , and the time of image formation by the image former  170 . This is because the positional deviation of the roller shaft and the pressure gradient between the rollers may occur due to the machine tolerance between the secondary transfer roller  431  and the opposing roller  44 , for example, at the time of replacement of members such as the secondary transferor  43  configuring the image forming apparatus  100  or the like. The controller  110  calculates the first movement amount, the second movement amount, and the difference between the first movement amount and the second movement amount at an arbitrary timing such as a timing at which the instruction input on the operation display  140  or the like from the user is received. The controller  110  calculates the first movement amount, the second movement amount, and the difference between the first movement amount and the second movement amount at timing when a change in at least one of the internal temperature and the external temperature of the image forming apparatus  100  becomes a predetermined amount or more. The internal temperature and the external temperature of the image forming apparatus  100  can be obtained by, for example, an installed internal temperature sensor and an external temperature sensor (both not illustrated), respectively. This is because expansion and contraction of the members of the image forming apparatus  100  due to changes in the internal temperature and the external temperature affect the pressure gradient between the rollers. The relation between the internal temperature and the like and the change in the difference between the first movement amount and the second movement amount is obtained from experiments and the like, thereby the predetermined amount can be set to an appropriate value from the viewpoint of the quality of the printed matter and the occurrence rate of jams in the conveyance of the sheet  900  and the like. The predetermined amount may be set as, for example, 10° C. 
     The controller  110  calculates the first movement amount and the second movement amount based on the detection result by the belt position detecting unit  81  in a state where at least one of the first movement amount and the second movement amount is adjusted to be zero by the steering roller  46 . 
     The controller  110  causes the operation display  140  to display the calculation results of the first movement amount and the second movement amount, the difference between the first movement amount and the second movement amount, the parallelism between the rollers, and the pressure gradient between the rollers. 
     The controller  110  causes the roller position adjuster  80  to adjust the position of both ends or one end of the secondary transfer roller  431  in the pressing direction to the opposing roller  44  based on any one of the first movement amount and the second movement amount, the difference between the first movement amount and the second movement amount, the parallelism between the rollers, and the pressure gradient between the rollers such that the secondary transfer roller  431  and the opposing roller  44  are in parallel. That is, the controller  110  adjusts the position of both ends or one end of the secondary transfer roller  431  in the pressing direction to the opposing roller  44  by adjusting the rotation angle of the cam  82  (see  FIG. 5 ) of the roller position adjuster  80 , such that the difference between the first movement amount and the second movement amount becomes zero. 
     The rotation angle of the cam  82  of the roller position adjuster  80  can be adjusted according to the adjustment amount according to a user instruction input to the operation display  140 . That is, the position of both ends or one end of the secondary transfer roller  431  in the pressing direction to the opposing roller  44  can be adjusted manually. In this case, the controller  110  outputs at least one of the first movement amount and the second movement amount, the difference between the first movement amount and the second movement amount, the parallelism between the rollers, and the pressure gradient between the rollers to the user by display on the operation display  140  or transmission from the communicator  130  to the terminal of the user or the like. Accordingly, the user adjusts the position of both ends or one end of the secondary transfer roller  431  in the pressing direction to the opposing roller  44  by adjusting the rotation angle and the like of the cam  82  based on the output information, such that the secondary transfer roller  431  and the opposing roller  44  are in parallel. Note that the rotation angle of the cam  82  of the roller position adjuster  80  may be adjusted by the adjustment amount by the force of the user. For example, a knob (not illustrated) as an adjustment mechanism may be provided on the rotation shaft  82   a  of the cam  82 , and the rotation angle of the cam  82  may be adjusted by rotating the knob by the force of the user. 
     The operation of the image forming apparatus  100  will be described. 
       FIG. 8  is a flowchart illustrating the operation of the image forming apparatus  100 . This flowchart can be executed by the controller  110  according to the program stored in the storage  120 . 
     The controller  110  determines whether or not there is the input of the instruction by the user to adjust the shaft position deviation in the operation display  140  (S 101 ). 
     When it is determined that there is not the input of the instruction by the user to adjust the shaft position deviation in the operation display  140  (S 101 : NO), the controller  110  repeatedly executes Step S 101 . 
     When it is determined that there is the input of the instruction by the user to adjust the shaft position deviation in the operation display  140  (S 101 : YES), the controller  110  starts the traveling of the intermediate transfer belt  42  in a state where the secondary transfer roller  431  and the opposing roller  44  are separated (S 102 ). 
     The controller  101  determines whether or not a predetermined time has elapsed since the start of the traveling of the intermediate transfer belt  42  by using a timer (not illustrated) built in the image forming apparatus  100  (S 103 ). 
     When it is not determined that the predetermined time has elapsed since the start of the traveling of the intermediate transfer belt  42  (S 103 : NO), the controller  101  repeatedly executes Step S 103 . 
     When it is determined that the predetermined time has elapsed since the start of the traveling of the intermediate transfer belt  42  (S 103 : YES), the controller  101  calculates the belt movement amount in the predetermined time as the first movement amount based on the detection result of the position of the intermediate transfer belt  42  by the belt position detecting unit  81  (S 104 ). 
     Thereafter, the controller  101  starts the traveling of the intermediate transfer belt  42  in a state where the secondary transfer roller  431  and the opposing roller  44  are pressed (S 105 ). 
     The controller  101  determines whether or not a predetermined time has elapsed since the start of the traveling of the intermediate transfer belt  42  by using the timer (S 106 ). 
     When it is not determined that the predetermined time has elapsed since the start of the traveling of the intermediate transfer belt  42  (S 106 : NO), the controller  101  repeatedly executes Step S 106 . 
     When it is determined that the predetermined time has elapsed since the start of the traveling of the intermediate transfer belt  42  (S 106 : YES), the controller  101  calculates the belt movement amount in the predetermined time as the second movement amount based on the detection result of the position of the intermediate transfer belt  42  by the belt position detecting unit  81  (S 107 ). 
     The controller  101  calculates the difference between the first movement amount and the second movement amount (S 108 ). 
     The controller  101  adjusts the parallelism between the rollers by the roller position adjuster  80 , such that the difference between the first movement amount and the second movement amount becomes zero (S 109 ). 
     Second Embodiment 
     A second embodiment of the present invention will be described. This embodiment differs from the first embodiment in the following points. In the first embodiment, the driving forces of the two drive motors  84  are converted into driving forces for changing the positions of both ends of the shaft of the secondary transfer roller  431  by the two cams  82 , respectively. On the other hand, in this embodiment, the driving force of one drive motor  84  is converted to the driving forces of changing the positions of both ends of the shaft of the secondary transfer roller  431  by two cams  82  which have a common rotation shaft and of which the shapes are different when viewed from the direction of the rotation shaft. In other points, this embodiment is the same as the first embodiment, and redundant description is omitted. 
       FIG. 9  is an explanatory diagram illustrating the operation of the roller position adjuster  80  when the parallelism between the rollers is adjusted by the roller position adjuster  80 . 
     The spring-included sheet metal  83  and the cam  82  are provided at positions corresponding to both ends of the secondary transfer roller  431 , respectively. The common rotation shaft  82   a  of the two cams  82  is rotationally driven by one drive motor  84 . The two cams  82  have different shapes when viewed from the direction of the rotation shaft  82   a , as indicated by thin arrows. Accordingly, the roller position adjuster  80  adjusts the positions of the both ends of the secondary transfer roller  431  in the pressing direction (the direction of the thick arrow) with different adjustment amounts of the push-up amount of each spring-included sheet metal  83  by the rotation of each cam  82 . That is, the parallelism between the rollers and the pressure gradient between the rollers are adjusted by the rotation driving of the two cams  82  by one drive motor  84 . 
       FIGS. 10A to 10D  are explanatory diagrams illustrating examples of the shape of the two cams  82  when viewed from the direction of the rotation shaft  82   a . In  FIGS. 10A to 10D , the cam  82 (F) arranged at a position corresponding to the front side of the secondary transfer roller  431  and the cam  82 (R) arranged at a position corresponding to the rear side are illustrated to be distinguished by solid lines and broken lines, respectively. Further, the points where the two cams  82 (F) and  82 (R) are in contact with the spring-included sheet metal  83  are indicated by a solid circle  83   a (F) and a broken circle  83   a (R), respectively. 
     As illustrated in  FIGS. 10A to 10D , in one cam  82 (F) and the other cam  82 (R) of the two cams  82 , the shapes of the two cams  82  when viewed from the direction of the rotation shaft  82   a  are different. Accordingly, by rotating the two cams  82 (F) and  82 (R) about the common rotation shaft  82   a , at the rotation angles of  FIGS. 10B and 10C , the push-up amounts by which the cams  82 (F) and  82 (R) push up the spring-included sheet metal  83  are different from each other. That is, the push-up amount of each spring-included sheet metal  83  is adjusted by different adjustment amounts by one drive motor  84 . At the rotation angles of  FIGS. 10A and 10D , the push-up amounts by which the cams  82 (F) and  82 (R) push up the spring-included sheet metal  83  are the same. However, the push-up amount of the spring-included sheet metal  83  in  FIG. 10A  is different from the push-up amount of the spring-included sheet metal  83  in  FIG. 10D . Thus, by changing the rotation angle in  FIG. 10A  into the rotation angle in  FIG. 10D , the pressure between the rollers is increased without adjusting the parallelism between the rollers and the pressure gradient between the rollers. 
     Third Embodiment 
     A third embodiment of the present invention will be described. This embodiment differs from the first embodiment in the following points. In the first embodiment, the parallelism between the secondary transfer roller  431  and the opposing roller  44  is adjusted. On the other hand, in this embodiment, the parallelism between the fixing roller  51   a  of the fixer  50  and the pressure roller  52  is adjusted. In other points, this embodiment is the same as the first embodiment, and redundant description is omitted. 
     The fixing roller  51   a  and the pressure roller  52  are pressed and separated via the fixing belt  51   b . Therefore, similarly to the first embodiment, the first movement amount can be calculated when the fixing belt  51   b  is made to travel for a predetermined time in a state where the fixing roller  51   a  and the pressure roller  52  are separated from each other. The second movement amount can be calculated when the fixing belt  51   b  is made to travel for the predetermined time in a state where the fixing roller  51   a  and the pressure roller  52  are pressed. Then, the parallelism between the fixing roller  51   a  and the pressure roller  52  of the fixer  50  can be adjusted based on the first movement amount and the second movement amount. 
     In this embodiment, for example, the belt position detector  81  is configured by a line sensor arranged along the width direction of the fixing belt  51   b , and the position of the fixing belt  51   b  in the width direction with respect to the fixing roller  51   a  is detected based on the light reflectance, which is measured by the line sensor, by the fixing roller  51   a  and the fixing belt  51   b . The first movement amount and the second movement amount are calculated based on the detection result of the belt position detector  81 . 
     Fourth Embodiment 
     A fourth embodiment of the present invention will be described. This embodiment differs from the first embodiment in the following points. In the first embodiment, the parallelism between the secondary transfer roller  431  and the opposing roller  44  is adjusted. On the other hand, in this embodiment, the parallelism between the photosensitive drum  47  as an image carrier and the primary transfer roller  48  is adjusted. In other points, this embodiment is the same as the first embodiment, and redundant description is omitted. 
     The photosensitive drum  47  and the primary transfer roller  48  are pressed and separated via the intermediate transfer belt  42 . Therefore, similarly to the first embodiment, when the intermediate transfer belt  42  is made to travel for the predetermined time in a state where the photosensitive drum  47  and the primary transfer roller  48  are separated from each other, the first movement amount can be calculated based on the detection result of the belt position detector  81 . In addition, when the intermediate transfer belt  42  is made to travel for the predetermined time in a state where the photosensitive drum  47  and the primary transfer roller  48  are pressed, the second movement amount can be calculated based on the detection result of the belt position detector  81 . Then, the parallelism between the photosensitive drum  47  and the primary transfer roller  48  can be adjusted based on the first movement amount and the second movement amount. 
     Fifth Embodiment 
     A fifth embodiment of the present invention will be described. This embodiment differs from the first embodiment in the following points. The image forming apparatus  100  of the first embodiment forms the image on the sheet  900  by an intermediate transfer system (tandem system). On the other hand, this embodiment is the image forming apparatus  100  using a direct transfer system of directly transferring an image from the photosensitive drum  47  as an image carrier to the sheet  900 . In other points, this embodiment is the same as the first embodiment, and redundant description is omitted. 
       FIG. 11  is an explanatory diagram illustrating the configuration of the photosensitive drum  47  and a transfer roller  49   a  of the image forming device  40  of the image forming apparatus  100 .  FIG. 11  illustrates a state where the photosensitive drum  47  and the transfer roller  49   a  are pressed via a transfer belt  49   b . Four combinations of the pressed photosensitive drum  47  and the transfer roller  49   a  are shown, and the combinations are provided to transfer the toner image with the toner of each color of Y, M, C, and K to the sheet  900 . The toner image with each color is formed at a position on each photosensitive drum  47  corresponding to the position of each photosensitive drum  47  in the sub-scanning direction indicated by an arrow. The color toner image is formed on the sheet  900  by forming the toner image of each color on the sheet  900  in an overlapping manner. 
     The photosensitive drum  47  and the transfer roller  49   a  are pressed and separated from each other via the transfer belt  49   b . Therefore, similarly to the first embodiment, the first movement amount can be calculated when the transfer belt  49   b  is made to travel for a predetermined time in a state where the photosensitive drum  47  and the transfer roller  49   a  are separated from each other. The second movement amount can be calculated when the transfer belt  49   b  is made to travel for the predetermined time in a state where the photosensitive drum  47  and the transfer roller  49   a  are pressed. Then, the parallelism between the photosensitive drum  47  and the transfer roller  49   a  can be adjusted based on the first movement amount and the second movement amount. 
     In this embodiment, the belt position detector  81  is configured by, for example, a line sensor arranged along the width direction of the transfer belt  49   b , and the position of the transfer belt  49   b  in the width direction with respect to the transfer roller  49   a  is detected based on the light reflectance, which is measured by the line sensor, by the transfer roller  49   a  and the transfer belt  49   b . The first movement amount and the second movement amount are calculated based on the detection result of the belt position detector  81 . 
     The embodiment described above has the following effects. 
     The first movement amount of the belt in the axial direction of the roller when the belt is made to travel for the predetermined time in the state where the roller pair that can be pressed and separated via the belt is separated and the second movement amount of the belt in the axial direction of the roller when the belt is made to travel for the predetermined time in the pressed state are calculated. Accordingly, the axial pressure gradient between the rollers can be reduced easily and accurately based on the calculation result. 
     Further, the difference between the first movement amount and the second movement amount is calculated. Accordingly, it is possible to easily reduce the pressure gradient between the rollers in the axial direction by adjusting the parallelism of the roller pair. 
     Further, at least one of the parallelism between the two rollers and the gradient of the pressure with respect to the axial direction of two rollers is calculated based on the first movement amount and the second movement amount. Accordingly, it is possible to more easily reduce the pressure gradient between the rollers in the axial direction by adjusting the parallelism of the roller pair. 
     Further, the first movement amount and the second movement amount are calculated at at least one timing of the time of replacement of members configuring the image forming apparatus, the time of shipment of the image forming apparatus, and the time of starting the image forming operation. Accordingly, the pressure gradient between the rollers in the axial direction can be reduced effectively. 
     Further, the first movement amount and the second movement amount are calculated at timing when a change in at least one of the internal temperature and the external temperature of the image forming apparatus becomes a predetermined amount or more. Accordingly, the pressure gradient between the rollers in the axial direction can be reduced more effectively. 
     Further, the first movement amount and the second movement amount are calculated at an arbitrary timing. Accordingly, it is possible to flexibly reduce the pressure gradient between the rollers in the axial direction at a desired timing according to the request of the user. 
     Further, the first movement amount and a second movement amount are calculated in a state where any one of the first movement amount and the second movement amount is adjusted to be zero by the steering mechanism which adjusts the movement of the position of the belt at the time of the traveling of the belt. Accordingly, it is possible to reduce the pressure gradient between the rollers in the axial direction with higher accuracy. 
     Further, the two rollers are set as at least one of the roller pair including the image carrier of the primary transferor for transferring the toner from the image carrier onto the belt, the roller pair of the secondary transferor for transferring the toner on the belt to the recording medium, and the roller pair of the fixer for fixing the toner on the recording medium. Accordingly, it is possible to effectively improve the quality of the printed matter and prevent the conveyance failure of the sheet. 
     Further, the two rollers are the roller pair including the image carrier of the direct transfer type transferor that transfers the toner from the image carrier to the recording medium. Accordingly, it is possible to effectively improve the quality of the printed matter and prevent the conveyance failure of the sheet. 
     Further, the adjuster is provided which can adjust the parallelism of each shaft of the two rollers by adjusting the position of at least one of the two rollers based on the first movement amount and the second movement amount or the adjustment index calculated from the first movement amount and the second movement amount. Accordingly, it is possible to flexibly reduce the pressure gradient between the rollers in the axial direction by hand, software, or hardware. 
     Further, the outputter is provided which outputs at least one of the first movement amount and the second movement amount, and the adjustment index to a user. The adjuster includes the adjustment mechanism that adjusts the position of at least one of two rollers according to the instruction input by the user or the adjustment amount by the force of the user and adjusts the parallelism of each shaft of the two rollers by the adjustment mechanism. Accordingly, the user manually adjusts the position of at least one of the two rollers with reference to the output results of the first movement amount, the second movement amount, and the like, so that the pressure gradient between the rollers in the axial direction can be accurately adjusted. 
     Further, the adjuster adjusts the parallelism of the shafts of the two rollers, by adjusting the position of at least one of the two rollers, based on the first movement amount and the second movement amount, or the adjustment index by two drive sources respectively arranged on both sides of at least one shaft of the two rollers and the conversion mechanism that converts driving forces of the two drive sources into respective driving forces of changing positions of both ends of the shaft. Accordingly, the pressure gradient between the rollers in the axial direction can be reduced with high accuracy without requiring any operation by the user. 
     Further, the adjuster includes one drive source, the first conversion mechanism that converts the driving force of the drive source into the driving force of changing the position of one end of the shaft of one of the two rollers, and the second conversion mechanism that converts the driving force of the drive source into the driving force of changing the position of another end of the shaft. The first conversion mechanism is a first cam that rotates about the rotation shaft by the driving force of the drive source so as to convert the driving force of the drive source into the driving force of changing the position of the one end of the shaft. The second conversion mechanism is the second cam that rotates about the rotation shaft together with the first cam by the driving force of the drive source so as to convert the driving force of the drive source into the driving force of changing the position of the other end of the shaft. Shapes of the first cam and the second cam when viewed from the direction of the rotation shaft are different. Accordingly, the pressure gradient between the rollers in the axial direction can be reduced with high accuracy without requiring any operation by the user and with a smaller number of members. 
     The display is further provided which displays the calculation result obtained by the arithmetic controller. Thereby, the parallelism of the roller pair or the like can be confirmed. 
     The invention is not limited to the embodiments described above. 
     For example, in the embodiment, the sheet has been described as the example of the storage medium, but the recording medium is not limited to the sheet, and may be a resin film or the like. 
     Further, some or all of the processing executed by the program in the embodiment may be executed by replacing hardware such as a circuit. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purpose of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims