Patent Publication Number: US-11021338-B2

Title: Sheet conveying device and image forming apparatus incorporating the sheet conveying device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-045716, filed on Mar. 13, 2018, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     This disclosure relates to a sheet conveying device, and an image forming apparatus incorporating the sheet conveying device. 
     Related Art 
     Image forming apparatuses include printing apparatuses that print a sheet while winding the sheet around a conveying drum as the sheet is conveyed. In such printing apparatuses, the sheet is to be gripped by the conveying drum on the circumferential surface of the conveying drum without crease on the sheet. 
     A known printing apparatus includes a holding member, a pair of contact-type pressing members, and multiple attraction holes. The holding member is mounted on an outer circumferential surface of a rotary drum to hold and grip the leading end of a recording medium in a sheet conveying direction. The pair of contact-type pressing members includes pressing members disposed upstream from the holding member in the sheet conveying direction and provided at both ends of the outer circumferential surface of the rotary drum. The pair of contact-type pressing members presses the recording medium toward the rotary drum by contacting the lateral side end of the recording medium. The multiple attraction holes are formed in the outer circumferential surface of the rotary drum to attract the non-image forming face side of the recording medium to be conveyed. 
     SUMMARY 
     At least one aspect of this disclosure provides a sheet conveying device including a conveying body, a pressing body, and an attracting device. The conveying body conveys a sheet. The pressing body presses the sheet to a circumferential surface of the conveying body at an upstream side from an operation start position at which an operation with respect to the sheet starts, in a sheet conveying direction. The attracting device sucks and attracts the sheet onto the conveying body. The attracting device includes an attracting unit having an attracting region extending shorter than a distance between the pressing body and the operation start position. The attracting unit rotates together with the conveying body. 
     Further, at least one aspect of this disclosure provides an image forming apparatus including an image forming device to form an image on a sheet, and the above-described sheet conveying device to convey the sheet to the image forming device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       An exemplary embodiment of this disclosure will be described in detail based on the following figured, wherein: 
         FIG. 1  is a schematic diagram illustrating an image forming apparatus (e.g., a printing apparatus) to discharge liquid, according to Embodiment 1 of this disclosure; 
         FIG. 2  is a schematic diagram illustrating a sheet conveying drum and components included in an attracting device; 
         FIG. 3  is a diagram illustrating the configuration of the attracting device; 
         FIG. 4  is a diagram illustrating control of attraction timings of an attraction controller; and 
         FIG. 5  is a diagram illustrating an example of relation of the size of a sheet in the width direction, attracting force, and time according to Embodiment 2 of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to” or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to” or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers referred to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements describes as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors herein interpreted accordingly. 
     Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layer and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. 
     The terminology used herein is for describing particular embodiments and examples and is not intended to be limiting of exemplary embodiments of this disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Descriptions are given, with reference to the accompanying drawings, of examples, exemplary embodiments, modification of exemplary embodiments, etc., of an image forming apparatus according to exemplary embodiments of this disclosure. Elements having the same functions and shapes are denoted by the same reference numerals throughout the specification and redundant descriptions are omitted. Elements that do not demand descriptions may be omitted from the drawings as a matter of convenience. Reference numerals of elements extracted from the patent publications are in parentheses so as to be distinguished from those of exemplary embodiments of this disclosure. 
     This disclosure is applicable to any image forming apparatus, and is implemented in the most effective manner in an inkjet image forming apparatus. 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes any and all technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of this disclosure are described. 
     Descriptions are given of an embodiment applicable to a sheet conveying device and an image forming apparatus incorporating the sheet conveying device, with reference to the following figures. 
     It is to be noted that identical parts are given identical reference numerals and redundant descriptions are summarized or omitted accordingly. 
     A description is given of an image forming apparatus  1  according to Embodiment 1 of this disclosure, with reference to  FIG. 1 . 
     The image forming apparatus  1  may be a copier, a facsimile machine, a printer, a multifunction peripheral or a multifunction printer (MFP) having at least one of copying, printing, scanning, facsimile, and plotter functions, or the like. According to the present example, the image forming apparatus  1  is an inkjet image forming apparatus that forms images on recording media by discharging ink. 
     It is to be noted in the following examples that: the term “image forming apparatus” indicates an apparatus in which an image is formed on a recording medium such as paper, OHP (overhead projector) transparencies, OHP film sheet, thread, fiber, fabric, leather, metal, plastic, glass, wood, and/or ceramic by attracting developer or ink thereto; the term “image formation” indicates an action for providing (i.e., printing) not only an image having meanings such as texts and figures on a recording medium but also an image having no meaning such as patterns on a recording medium; and the term “sheet” is not limited to indicate a paper material but also includes the above-described plastic material (e.g., an OHP sheet), a fabric sheet and so forth, and is used to which the developer or ink is attracted. In addition, the “sheet” is not limited to a flexible sheet but is applicable to a rigid plate-shaped sheet and a relatively thick sheet. 
     Further, size (dimension), material, shape, and relative positions used to describe each of the components and units are examples, and the scope of this disclosure is not limited thereto unless otherwise specified. 
     Further, it is to be noted in the following examples that: the term “sheet conveying direction” indicates a direction in which a recording medium travels from an upstream side of a sheet conveying path to a downstream side thereof; the term “width direction” indicates a direction basically perpendicular to the sheet conveying direction. 
       FIG. 1  is a schematic diagram illustrating the image forming apparatus (e.g., a printing apparatus) to discharge liquid, according to Embodiment 1 of this disclosure. 
     The image forming apparatus  1  includes a sheet feeding device  10 , a printing device  20 , a drying device  30 , and a sheet ejecting device  40 . The image forming apparatus  1  feeds a sheet P that is fed from the sheet feeding device  10 , prints an image on the sheet P by applying liquid in the printing device  20 , dries the liquid adhered to the sheet P in the drying device  30 , and ejects the sheet P to the sheet ejecting device  40 . 
     The sheet feeding device  10  includes a sheet feed tray  11 , a sheet feeding unit  12 , and a pair of registration rollers  13 . The sheet feed tray  11  loads multiple sheets P. The sheet feeding unit  12  separates the multiple sheets P fed from the sheet feed tray  11  one by one and feeds an uppermost sheet P of the multiple sheets P toward the printing device  20  that functions as an image forming device. 
     The sheet feeding unit  12  may be a sheet feeding unit that includes rollers, a sheet feeding unit employing an air suction method, and any other sheet feeding units. After the sheet P has been fed from the sheet feed tray  11  by the sheet feeding unit  12 , as the leading end of the sheet P reaches the pair of registration rollers  13 , the pair of registration rollers  13  drives and rotates at a predetermined timing to convey the sheet P to the printing device  20 . 
     The printing device  20  includes a sheet conveying drum  21  and a liquid discharging device  22 . The sheet conveying drum  21  functions as a conveying body to convey the sheet P while gripping the sheet P on an outer circumferential surface of the sheet conveying drum  21 . The liquid discharging device  22  discharges liquid toward the sheet P that is borne on the sheet conveying drum  21 . 
     The printing device  20  further includes a transfer cylinder  24  and a transfer cylinder  25 . The transfer cylinder  24  receives the sheet P from the sheet feeding device  10  and transfers the sheet P to the sheet conveying drum  21 . The transfer cylinder  25  receives the sheet P that is conveyed by the sheet conveying drum  21  and transfers the sheet P to the drying device  30 . 
     After the sheet P has been conveyed from the sheet feeding device  10  to the printing device  20 , the leading end of the sheet P is gripped b a sheet gripper that is mounted on the surface of the transfer cylinder  24 , so that the sheet P is conveyed along with rotation of the transfer cylinder  24 . The sheet P conveyed by the transfer cylinder  24  is transferred to the sheet conveying drum  21  at an opposing position where the sheet P is brought to face the sheet conveying drum  21 . 
     Another sheet gripper is mounted on the surface of the sheet conveying drum  21 , so that the leading end of the sheet P is gripped by the sheet gripper of the sheet conveying drum  21 . Multiple suction holes are dispersedly formed in the surface of the sheet conveying drum  21 . The printing device  20  further includes an attracting device  26  that functions as an attracting device and a liquid discharging device  22 . The attracting device  26  generates suction airflow directed inward from the multiple suction holes of the sheet conveying drum  21 . 
     After the sheet P is conveyed from the transfer cylinder  24  to the sheet conveying drum  21 , the leading end of the sheet P is gripped by the sheet gripper of the sheet conveying drum  21  and, at the same time, the sheet P is attracted onto the sheet conveying drum  21  due to suction airflow generated by the attracting device  26 . Accordingly, the sheet P is conveyed along with rotation of the sheet conveying drum  21 . The sheet conveying drum  21 , the attracting device  26 , and a leveling roller  28  (described later) are included in a sheet conveying device  100 . 
     The liquid discharging device  22  includes a liquid discharging unit  23  (to be more specific, liquid discharging units  23 A,  23 B,  23 C, and  23 D). For example, the liquid discharging unit  23 A discharges liquid of cyan (C), the liquid discharging unit  23 B discharges liquid of magenta (M), the liquid discharging unit  23 C discharges liquid of yellow (Y), the liquid discharging unit  23 D discharges liquid of black (K). It is to be noted that another liquid discharging unit that discharges liquid of special color such as white, gold, and silver or liquid such as surface coating liquid may be provided, according to a user&#39;s request. 
     Respective liquid discharging units  23 A,  23 B,  23 C, and  23 D of the liquid discharging device  22  are controlled by respective drive signals according to printing information. When the sheet P that is borne on the sheet conveying drum  21  passes an opposing region facing the liquid discharging device  22 , liquid of respective colors (i.e., cyan, magenta, yellow, and black) is discharged from the liquid discharging unit  23  (i.e., the liquid discharging units  23 A,  23 B,  23 C, and  23 D), so that an image according to the printing information is formed. 
     The drying device  30  includes a drying mechanism  31  and a suction and conveyance mechanism  32 . The drying mechanism  31  dries liquid that is adhered onto the sheet P in the printing device  20 . The suction and conveyance mechanism  32  conveys the sheet P that is conveyed from the printing device  20  while sucking the sheet P (in other words, simultaneously performs suction and conveyance of the sheet P). 
     The sheet P that is conveyed from the printing device  20  is received by the suction and conveyance mechanism  32 . Then, the sheet P is conveyed to pass through the drying mechanism  31  and is transferred to the sheet ejecting device  40 . 
     When passing through the drying mechanism  31 , the liquid on the sheet P is subjected to a drying operation performed by the drying mechanism  31 . According to the drying operation by the drying mechanism  31 , moisture such as water in the liquid evaporates. Consequently, the colorant contained in the liquid is fixed to the sheet P, and curling of the sheet P is restrained. 
     The sheet ejecting device  40  includes a sheet ejection tray  41  on which multiple sheets P are loaded. The sheets P that are sequentially conveyed from the drying device  30  are overlaid one after another on the sheet ejection tray  41  and stacked. 
     It is to be noted that the image forming apparatus  1  may include a pre-processing device that performs pre-processing to the sheet P and locate the pre-processing device upstream from the printing device  20  in the sheet conveying direction or include a post-processing device that performs post-processing to the sheet P and locate the post-processing device between the drying device  30  and the sheet ejecting device  40 . 
     As an example of the pre-processing, for example, a pre-coating operation is performed to apply processing liquid to a sheet P in order to restrain bleeding of liquid reacting to the liquid. In addition, as an example of the post-processing, for example, a sheet reversing and conveying process to reverse a sheet printed in the printing device  20  and send the sheet again to the printing device  20  so as to print both sides of the sheet, and a binding process to bind multiple sheets. 
     Next, a description is given of the attracting device  26 , with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a schematic diagram illustrating the sheet conveying drum  21  and components around the sheet conveying drum  21  included in the attracting device  26 .  FIG. 3  is a diagram illustrating the configuration of the attracting device  26  of  FIG. 2 . 
     First, referring to  FIG. 2 , a leveling roller  28  is disposed in the vicinity of the sheet conveying drum  21 , upstream from the liquid discharging unit  23  (to be more specific, the liquid discharging unit  23 A) in the sheet conveying direction, and downstream from the transfer cylinder  24  in the sheet conveying direction. The leveling roller  28  functions as a pressing body to press the sheet P to the outer circumferential surface of the sheet conveying drum  21 . As previously described, the leveling roller  28  is included in the sheet conveying device  100 . 
     Specifically, in the present embodiment, the printing device  20  performs a printing operation that is a predetermined operation to the sheet P, and an operation start position at which the printing operation (i.e., the predetermined operation) of the printing device  20  (hereinafter, referred to as a “printing operation start position”) equals a liquid discharging position at which the liquid discharging unit  23 A that is an extreme upstream side liquid discharging unit of the liquid discharging units  23 A,  23 B,  23 C, and  23 D discharges liquid. 
     By gripping the leading end of the sheet P by the sheet gripper of the sheet conveying drum  21  and pressing the trailing end of the sheet P by the leveling roller  28 , a tension force is applied to the sheet P. As a result, crease and lifting of the sheet P are corrected, and therefore the sheet P is borne on the sheet conveying drum  21  along the outer circumferential surface of the sheet conveying drum  21 . 
     An attracting unit (or a suction unit)  201  (i.e., attracting units  201 A,  201 B, and  201 C) that forms the attracting device  26  is disposed inside the sheet conveying drum  21 . The attracting unit  201  rotates in cooperation with rotation of the sheet conveying drum  21 . 
     The attracting units  201 A,  201 B, and  201 C include respective attraction regions (i.e., sucking regions) having respective lengths L 1 , L 2 , and L 3  shorter or smaller than a distance L 0  extending from the leveling roller  28  to the printing operation start position of the liquid discharging unit  23 A as an extreme upstream liquid discharging unit. The relations of the lengths L 1 , L 2 , and L 3  to the distance L 0  are expressed as L 1 &lt;L 0 , L 2 &lt;L 0 , and L 3 &lt;L 0 . 
     In the present embodiment, the sheet conveying drum  21  is capable of bearing multiple sheets P at the same time and includes the attracting units  201 A,  201 B, and  201 C that are divided in three according to the length of a single sheet P. However, the configuration of the sheet conveying drum  21  is not limited to this configuration. 
     In the above-described configuration of the sheet conveying drum  21 , the lengths of the respective attraction regions of the attracting units  201 A,  201 B, and  201 C may not be equal to each other. For example, in consideration of the corresponding size of the sheet P, the length of the attraction region of the attracting unit  201  is adjusted to the smallest size, in other words, the minimum size. Therefore, the attracting unit that is disposed on the extreme downstream side in the sheet conveying direction (in this case, the attracting unit  201 C) has the longest attraction region. Since the other attraction regions closer to the trailing end of the sheet P is determined according to division of the sheet P, the respective lengths of the other attraction regions are shorter than the length of attraction region of the extreme downstream side attracting unit. 
     However, the length of the attraction region of the attracting unit  201  on the extreme downstream side in the sheet conveying direction is shorter (smaller) than the distance extending from the leveling roller  28  (i.e., a pressing body) to the printing operation start position at which the liquid discharging unit  23 A that is disposed on the extreme upstream side in the sheet conveying direction. 
     Next, referring to  FIG. 3 , the attracting device  26  further includes dedicated suction passages  202 , a common suction passage  203 , and a suction pump  204 . The attracting unit  201  (i.e., the attracting units  201 A,  201 B, and  201 C) of the attracting device  26  is coupled to the suction pump  204  that functions as a suction body, via the dedicated suction passages  202  and the common suction passage  203 . The respective dedicated suction passages  202  are provided with each electromagnetic valve  205  (specifically, electromagnetic valves  205 A,  205 B, and  205 C) that functions as an opening and closing body. 
     The attracting device  26  further includes an attraction controller  501  that performs control of driving of the suction pump  204  and control of opening and closing of the electromagnetic valve  205  (i.e., the electromagnetic valves  205 A,  205 B, and  205 C). 
     The attraction controller  501  is connected to a home sensor  502  and a rotary encoder  503 . The home sensor  502  outputs a home position signal according to rotation of the sheet conveying drum  21 . The rotary encoder  503  obtains a count value of the output pulses. The attraction controller  501  detects the respective positions of the attracting units  201 A,  201 B, and  201 C relative to the leveling roller  28  based on the home position signal of the home sensor  502  and the count value of the output pulses of the rotary encoder  503 . Based on the result, the attraction controller  501  controls opening and closing of the electromagnetic valve  205  (i.e., the electromagnetic valves  205 A,  205 B, and  205 C) to control attraction of the sheet P performed by the attracting unit  201  (i.e., the attracting units  201 A,  201 B, and  201 C). 
     Next, a description is given of attraction control performed by the attraction controller  501 , with reference to drawings including  FIG. 4 . 
       FIG. 4  is a diagram illustrating timings of attraction control of the attraction controller  501 . 
     First, the transfer cylinder  24  conveys the sheet P to the sheet conveying drum  21 . Then, the sheet gripper of the sheet conveying drum  21  grips the leading end of the sheet P, so that the sheet P is further conveyed along with rotation of the sheet conveying drum  21 . Then, as the sheet P passes through the leveling roller  28 , the sheet P receives a tension force. Accordingly, crease and lifting of the sheet P are corrected. 
     Here, for example, assuming that the leading end of the attracting unit  201 A passes the leveling roller  28  at a point in time t 0  as illustrated in the graph of  FIG. 4 , the attracting unit  201 A continues to halt the start of attraction of the sheet P from the point in time t 0 . 
     Then, at a point in time t 1  in the graph of  FIG. 4  after the trailing end of the attracting unit  201 A passes the leveling roller  28 , for example, the electromagnetic valve  205 A is opened and the attracting unit  201 A starts to attract the sheet P onto the sheet conveying drum  21 . In this case, the distance from the point in time t 0  to the point in time t 1  as illustrated in the graph of  FIG. 4  equals to a distance of the sum of the length L 1  of the attraction region of the attracting unit  201 A and an amount of margin α. 
     It is to be noted that this description is given without a time lag between the operation of the electromagnetic valve  205  and generation of an actual attracting force. However, when a time lag is generated, the electromagnetic valve  205  is opened earlier by the time lag. 
     Therefore, when the sheet P passes through the leveling roller  28  and is subjected to a tension force applied between the gripping at the leading end of the sheet P by the sheet gripper of the sheet conveying drum  21  and the leveling roller  28 , the sheet P is not attracted to the sheet conveying drum  21 . Accordingly, crease and lifting of the sheet P are corrected by the tension force. 
     By contrast, in a case in which the sheet P is attracted to the sheet conveying drum  21  when the sheet P has passed the leveling roller  28 , a frictional force that is generated between the sheet P and the sheet conveying drum  21  increases. Therefore, crease and lifting of the sheet P are fixed when the sheet P is attracted. As a result, even if the tension force is applied by the leveling roller  28 , the sheet P fails to be leveled. 
     Then, at a point in time t 2  in the graph of  FIG. 4  after the trailing end of the attracting unit  201 B passes the leveling roller  28 , for example, the electromagnetic valve  205 B is opened and the attracting unit  201 B starts attraction of the sheet P. In this case, the distance from the point in time t 1  to the point in time t 2  as illustrated in the graph of  FIG. 4  equals to a distance of the sum of the length L 1  of the attraction region of the attracting unit  201 A, the length L 2  of the attraction region of the attracting unit  201 B, and the amount of margin α. 
     Further, at a point in time t 3  in the graph of  FIG. 4  after the trailing end of the attracting unit  201 C passes the leveling roller  28 , for example, the electromagnetic valve  205 C is opened and the attracting unit  201 C starts attraction of the sheet P. In this case, the distance from the point in time t 1  to the point in time t 3  as illustrated in the graph of  FIG. 4  equals to a distance of the total of the sum of the length L 1  of the attraction region of the attracting unit  201 A, the length L 2  of the attraction region of the attracting unit  201 B, and the length L 3  of the attraction region of the attracting unit  201 C, subtracted by an amount of margin β. 
     Here, the amount of margin β is a length to be subtracted due to attraction of the attracting unit  201 C performed before the trailing end of the sheet P passes the leveling roller  28 . 
     Specifically, when the trailing end of the sheet P is being opposed to any part of the attracting unit  201 , the trailing end of the sheet P comes out of the leveling roller  28  without being attracted before the attracting unit  201  passes the leveling roller  28 . In a case in which the trailing end of the sheet P comes out of the leveling roller  28  without being attracted, it is likely that lifting of the sheet P occurs. 
     For example, in a comparative image forming apparatus, before a pair of contact-type pressing members presses a recording medium, an attracting member attracts the recording medium. As a result, the effect of leveling the recording medium onto the circumferential surface of a conveying drum by the pair of contact-type pressing members to restrain crease and lifting of the recording medium cannot be achieved sufficiently. 
     Therefore, in a case in which the trailing end of the sheet P is opposed to the attracting unit  201 , even before the attracting unit  201  passes the leveling roller  28 , the attracting unit  201  attracts the sheet P before the trailing end of the sheet P comes out of the leveling roller  28 . 
     As described above, when the trailing end of the sheet P is opposed to any part of the attracting unit  201 , the attracting device  26  causes the attracting unit  201  to attract the sheet P onto the sheet conveying drum  21  before the trailing end of the sheet P passes the leveling roller  28  (i.e., a pressing body). 
     Accordingly, the sheet P is prevented from lifting of the trailing end of the sheet P, and therefore is conveyed stably. 
     Further, for example, even when the trailing end of the sheet P is opposed to any part of the attracting unit  201 B or when the sheet P corresponds to a sheet having the size to be opposed to the attracting unit  201 A, it is preferable that the attracting unit  201  attracts the sheet P onto the sheet conveying drum  21  before the trailing end of the sheet P passes the leveling roller  28 . 
     In other words, in a case in which the distance of attraction of the sheet P by the attracting unit  201  is shorter (smaller) than the distance L 0  that is the distance between the leveling roller  28  (i.e., a pressing body) and the printing operation start position, the attracting device  26  causes the attracting unit  201  to attract the sheet P onto the sheet conveying drum  21  before the trailing end of the sheet P passes the leveling roller  28 . 
     Accordingly, the sheet P is prevented from lifting of the sheet P, and therefore is conveyed stably. 
     Next, a description is given of an image forming apparatus  1  according to Embodiment 2, with reference to drawings including  FIG. 5 . 
       FIG. 5  is a diagram illustrating an example of relation of the size of a sheet in the width direction, attracting force, and time according to Embodiment 2 of this disclosure. 
     In the present embodiment, the attracting device  26  changes the timing to apply the attracting force of the attracting unit  201  according to the width in a direction perpendicular to the sheet conveying direction of the sheet P. 
     To be more specific, the wider the width in the direction perpendicular to the sheet conveying direction of the sheet P is, the smaller the number of suction holes that are not blocked by the sheet P becomes, among the multiple suction holes of the sheet conveying drum  21 . By contrast, the narrower the width in the direction perpendicular to the sheet conveying direction of the sheet P is, the greater the number of suction holes that are not blocked by the sheet P becomes. 
     Therefore, depending on the number of suction holes that not blocked by the sheet P, the time that is taken until the attracting force of the attracting unit  201  reaches a predetermined attracting force varies. For example, as illustrated in  FIG. 5 , the time from the start of the suction by the attracting unit  201  to the target attracting force takes longer (greater) in a case in which the width in the direction perpendicular to the sheet conveying direction of the sheet P is narrower with the smaller number of suction holes that are blocked by the sheet P than a case in which the width in the direction perpendicular to the sheet conveying direction of the sheet P is wider with the greater number of suction holes that are blocked by the sheet P. 
     Therefore, when the width of the sheet P is relatively wide, the timing of applying the attracting force (i.e., the timing of generating the suction force) is delayed, and when the width of the sheet material P is relatively narrow, the timing of applying the attracting force (i.e., the timing of generating the suction force) is made earlier. In this case, when a sheet having the largest applicable width (i.e., the maximum width applicable in the image forming apparatus  1 ) is conveyed, the timing of applying the attracting force to the sheet having the largest applicable width is the latest timing. Similarly, when a sheet having the smallest applicable width (i.e., the minimum width applicable in the image forming apparatus  1 ) is conveyed, the timing of applying the attracting force to the sheet having the smallest applicable width is the earliest timing. 
     Consequently, the sheet P is attracted stably. 
     For example, in the example of  FIG. 4 , when the electromagnetic valve  205 A is opened and the attracting unit  201 A attracts the sheet P at the point in time t 1 , the electromagnetic valve  205 A is opened earlier when the attracting unit  201 A attracts the sheet P having a narrower width than when the attracting unit  201 A attracts the sheet P having a wider width. With this operation, the attracting unit  201 A generates the target attracting force at the point in time t 1 . 
     It is to be noted that, in the present embodiment, the timing of applying the attracting force is controlled. However, the operation of the attracting device  26  is not limited thereto. For example, the suction force of the attracting unit  201  may also be changed according to the width of the sheet P. 
     The change of the suction force is achieved by changing the suction force of the suction pump  204  that functions as a suction body according to the width of the sheet P. According to this operation, the time until the attracting force of the attracting unit  201  reaches the target attracting force is substantially equal even though the width of the sheet P is relatively narrow or relatively wide. 
     It is to be noted that, each of the above-described embodiments provides an example in which the predetermined operation is a printing operation. However, the predetermined operation is not limited to the printing operation. For example, the predetermined operation may include a reading operation to read an image formed on a sheet and a detecting operation to detect a position detecting mark of a sheet and the leading end of a sheet. 
     In this disclosure, the term “liquid” that is used as liquid discharged from a liquid discharging unit includes any liquid having a viscosity or a surface tension that can be discharged from the liquid discharge head. However, preferably, the viscosity of the liquid is not greater than 30 mPa·s under ordinary temperature and ordinary pressure or by heating or cooling. Examples of the liquid include a solution, a suspension, or an emulsion that contains, for example, a solvent, such as water or an organic solvent, a colorant, such as dye or pigment, a functional material, such as a polymerizable compound, a resin, or a surfactant, a biocompatible material, such as DNA, amino acid, protein, or calcium, or an edible material, such as a natural colorant. Such a solution, a suspension, or an emulsion can be used for, e.g., inkjet ink, surface treatment solution, a liquid for forming components of electronic element or light-emitting element or a resist pattern of electronic circuit, or a material solution for three-dimensional fabrication. 
     Examples of an energy source for generating energy to discharge liquid include a piezoelectric actuator (a laminated piezoelectric element or a thin-film piezoelectric element), a thermal actuator that employs a thermoelectric conversion element, such as a heating resistor, and an electrostatic actuator including a diaphragm and opposed electrodes. 
     The term “liquid discharge apparatus” used herein is an apparatus including the liquid discharge head or the liquid discharge device to discharge liquid by driving the liquid discharge head. The liquid discharge apparatus may be, for example, an apparatus capable of discharging liquid to a material to which liquid can adhere and an apparatus to discharge liquid toward gas or into liquid. 
     The “liquid discharge apparatus” may include devices to feed, convey, and eject the material on which liquid can adhere. The liquid discharge apparatus may further include a pretreatment apparatus to coat a treatment liquid onto the material, and a post-treatment apparatus to coat a treatment liquid onto the material, onto which the liquid has been discharged. 
     The “liquid discharge apparatus” may be, for example, an image forming apparatus to form an image on a sheet by discharging ink, or a three-dimensional fabrication apparatus to discharge a fabrication liquid to a powder layer in which powder material is formed in layers to form a three-dimensional fabrication object. 
     The “liquid discharge apparatus” is not limited to an apparatus to discharge liquid to visualize meaningful images, such as letters or figures. For example, the liquid discharge apparatus includes an apparatus to form meaningless images, such as meaningless patterns, or fabricate three-dimensional images. 
     The above-described term “material onto which liquid adheres” denotes, for example, a material or a medium onto which liquid is adhered at least temporarily, a material or a medium onto which liquid is adhered and fixed, or a material or a medium onto which liquid is adhered and into which the liquid permeates. Examples of the “material onto which liquid adheres” include recording media such as a paper sheet, recording paper, and a recording sheet of paper, film, and cloth, electronic components such as an electronic substrate and a piezoelectric element, and media such as a powder layer, an organ model, and a testing cell. The “material onto which liquid adheres” includes any material on which liquid adheres unless particularly limited. 
     The above-mentioned “material onto which liquid adheres” may be any material as long as liquid can temporarily adhere such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, or the like. 
     The “liquid discharge apparatus” may be an apparatus to relatively move the liquid discharge head and a material on which liquid can be adhered. However, the liquid discharge apparatus is not limited to such an apparatus. For example, the “liquid discharge apparatus” may be a serial head apparatus that moves the liquid discharge head, a line head apparatus that does not move the liquid discharge head, or the like. 
     Examples of the “liquid discharge apparatus” further include a treatment liquid coating apparatus to discharge the treatment liquid to a sheet to coat the treatment liquid on a sheet surface to reform the sheet surface and an injection granulation apparatus in which a composition liquid including raw materials dispersed in a solution is discharged through nozzles to granulate fine particles of the raw materials. Further, there is an injection granulation apparatus for spraying a composition liquid in which raw materials are dispersed in a solution through a nozzle to granulate fine particles of the raw material. 
     The terms “image formation”, “recording”, “printing”, “image printing”, and “fabricating” used herein may be used synonymously with each other. 
     The above-described embodiments are illustrative and do not limit this disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements at least one of features of different illustrative and exemplary embodiments herein may be combined with each other at least one of substituted for each other within the scope of this disclosure and appended claims. Further, features of components of the embodiments, such as the number, the position, and the shape are not limited the embodiments and thus may be preferably set. It is therefore to be understood that within the scope of the appended claims, the disclosure of this disclosure may be practiced otherwise than as specifically described herein.