Patent Publication Number: US-11385588-B2

Title: Sheet laminator, image forming apparatus, and image forming system

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. 2020-111643, filed on Jun. 29, 2020, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure relate to a sheet laminator that performs a sheet lamination on a two-ply sheet in which an inner sheet is inserted, an image forming apparatus (for example, a copier, a printer, a facsimile machine, and a multi-functional apparatus having at least two functions of the copier, the printer, and the facsimile machine) including the sheet laminator, and an image forming system including the sheet laminator. 
     Background Art 
     Various types of sheet laminators are known to perform the sheet laminating operation on a two-ply sheet in which two sheets are bonded together at a bonding portion on one end of the two-ply sheet after the two sheets of the two-ply sheet are separated and an inner sheet is inserted into the two-ply sheet with the two sheets being separated. 
     Specifically, a known sheet laminator separates two sheets of a laminated sheet (that is a two-ply sheet) in which one sides of the two sheets are bonded at one end of the two-ply sheet, and inserts protective paper that is an inner sheet between the two sheets. Then, the lamination sheet in which the protective paper is inserted is conveyed to a portion (lamination portion) in which a heater is disposed, so that the heater heats the lamination sheet to perform the sheet lamination. 
     SUMMARY 
     Embodiments of the present disclosure described herein provide a novel sheet laminator including a sheet separation device, a sheet insertion device, and circuitry. The sheet separation device is configured to perform a sheet separating operation to separate a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at one end as a bonding portion of the two-ply sheet, and a sheet inserting operation to insert an inner sheet between the two sheets separated from each other by the sheet separating operation. The sheet lamination device is configured to perform a sheet laminating operation on the two-ply sheet after the sheet separating operation and the sheet inserting operation performed by the sheet separation device. The circuitry is configured to cause the sheet lamination device to perform the sheet laminating operation on the two-ply sheet while causing the sheet separation device to perform the sheet separating operation on another two-ply sheet subsequent to the two-ply sheet or the sheet separating operation and the sheet inserting operation on said another two-ply sheet. 
     Further, embodiments of the present disclosure described herein provide an image forming apparatus including a housing that includes an image forming apparatus that is configured to form an image on a sheet, and the above-described sheet laminator. 
     Further, embodiments of the present disclosure described herein provide an image forming system including an image forming apparatus that is configured to form an image on a sheet, and the above-described sheet laminator that is detachably attached to the image forming apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Exemplary embodiments of this disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic view illustrating the overall configuration of a sheet laminator according to an embodiment of the present disclosure; 
         FIG. 2A  is a side view illustrating a gripper that has moved to a gripping position in the sheet laminator illustrated in  FIG. 1 ; 
         FIG. 2B  is a side view illustrating the gripper that has moved to a releasing position in the sheet laminator illustrated in  FIG. 1 ; 
         FIG. 3A  is a perspective view illustrating the gripper that has moved to the gripping position in the sheet laminator illustrated in  FIG. 1 ; 
         FIG. 3B  is a perspective view illustrating the gripper that has moved to the releasing position in the sheet laminator illustrated in  FIG. 1 ; 
         FIGS. 4A to 4D  are schematic views, each illustrating the sheet separating operation performed in the sheet laminator illustrated in  FIG. 1 ; 
         FIGS. 5A to 5D  are schematic views, each illustrating the sheet separating operation performed in the sheet laminator, subsequent from the sheet separating operation of  FIGS. 4A to 4D ; 
         FIGS. 6A to 6C  are schematic views, each illustrating the sheet separating operation performed in the sheet laminator, subsequent from the sheet separating operation of each of  FIGS. 5A to 5D ; 
         FIGS. 7A to 7C  are schematic views, each illustrating the sheet separating operation performed in the sheet laminator, subsequent from the sheet separating operation of each of  FIGS. 6A to 6C ; 
         FIGS. 8A to 8C  are schematic views, each illustrating the sheet separating operation performed in the sheet laminator, subsequent from the sheet separating operation of each of  FIGS. 7A to 7C ; 
         FIGS. 9A to 9D  are schematic views, each illustrating the sheet separating operation performed in the sheet laminator, subsequent from the sheet separating operation of each of  FIGS. 8A to 8C ; 
         FIGS. 10A to 10C  are schematic views, each illustrating the sheet separating operation performed in the sheet laminator, subsequent from the sheet separating operation of each of  FIGS. 9A to 9D ; 
         FIG. 11  is a schematic view illustrating separation claws inserted into a two-ply sheet in a width direction of the two-ply sheet; 
         FIGS. 12A to 12E  are perspective views, each illustrating the operation of the separation claws; 
         FIG. 13  including  FIGS. 13A and 13B  is a flowchart illustrating a flow of a control process executed in the sheet laminator; 
         FIG. 14  is a flowchart illustrating the flow of the control process subsequent from  FIG. 13 ; 
         FIG. 15  is a schematic view illustrating the configuration of a moving mechanism to move the separation claws; 
         FIGS. 16A and 16B  are schematic views, each illustrating a part of operation in a sheet laminator, according to Variation 1; 
         FIG. 17  is a schematic view illustrating an image forming apparatus, according to Variation 2; and 
         FIG. 18  is a schematic view illustrating an image forming system, according to Variation 3. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     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. 
     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. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below. 
     Next, a description is given of a configuration and functions of a sheet laminator, an image forming apparatus, and an image forming system, according to an embodiment of the present disclosure, with reference to drawings. Note that identical parts or equivalents are given identical reference numerals and redundant descriptions are summarized or omitted accordingly. 
     First, a description is given of the overall configuration and operations of a sheet laminator  50 , with reference to  FIG. 1 . 
     The sheet laminator  50  includes a sheet separation device  1 , a sheet lamination device  51 , a first ejection tray  13 , a second ejection tray  55  that functions as a retract portion. 
     The sheet separation device  1  includes a first feed tray  11 , a second feed tray  12 , a first feed roller  2 , a second feed roller  3 , a first conveyance roller pair  4 , a second ejection roller pair  8 , a third conveyance roller pair  6 , a first sensor  41 , a second sensor  42 , a third sensor  43 , a fourth sensor  44 , a fifth sensor  45 , a sixth sensor  46 , a seventh sensor  47 , an eighth sensor  48 , a winding roller  20 , a moving mechanism  30 , and separation claws  16  (see  FIGS. 6A to 6C  and  FIGS. 12A to 12E ). Each of the separation claws  16  functions as a separator. The sheet separation device  1  further includes a controller  500  that controls sheet conveyance of the sheet (i.e., the two-ply sheet PJ and the inner sheet PM) by performing, e.g., a sheet separating operation, a sheet laminating operation, and a sheet inserting operation. The controller  500  is connected to various drivers driving various parts and units, for example, the above-described parts and units included in the sheet separation device  1 . 
     The sheet separation device  1  performs a sheet separating operation and a sheet inserting operation. To be more specific, the sheet separation device  1  performs the sheet separating operation to separate the non-bonding portion of a two-ply sheet PJ in which two sheets, which are a first sheet P 1  and a second sheet P 2 , are overlapped and bonded together at one end of the two-ply sheet PJ as a bonding portion A of the two-ply sheet PJ (see  FIGS. 12A to 12E  and other drawings). The sheet separation device  1  then performs the sheet inserting operation to insert an inner sheet PM between the first sheet P 1  and the second sheet P 2  separated from each other by the sheet separating operation. 
     In particular, in the present embodiment, the two-ply sheet PJ is made of the first sheet P 1  and the second sheet P 2  overlapped and bonded together at one side of four sides as the bonding portion A. That is, in the two-ply sheet PJ including the first sheet P 1  and the second sheet P 2 , one side (the bonding portion A) of the first sheet P 1  and one side (the bonding portion A) of the second sheet P 2  are connected by, e.g., thermal welding, and the other side of the first sheet P 1  and the other side of the second sheet P 2  are not connected. As the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ, a transparent film sheet (that is, a laminated sheet) may be employed. 
     The sheet separation device  1  separates the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ, in other words, separates the other side of the two sheets that is opposite the bonding portion A that maintains bonding of the first sheet P 1  and the second sheet P 2 . Subsequently, the sheet separation device  1  inserts an inner sheet PM between the separated two sheets, which are the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ. The inner sheet PM is a sheet including at least one plain sheet or a photograph. 
     The sheet lamination device  51  performs the sheet laminating operation on the two-ply sheet PJ after the sheet separating operation and the sheet inserting operation are performed on the two-ply sheet PJ by the sheet separation device  1 . 
     Specifically, the sheet lamination device  51  performs the sheet laminating operation on the two-ply sheet PJ in a state in which the inner sheet PM is inserted between two sheets, which are the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ, separated from each other by the sheet separation device  1 . In other words, the sheet lamination device  51  applies heat and pressure on the non-bonding portion of the two sheets (i.e., the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ) to bond the two sheets together in a state in which the inner sheet PM. The sheet lamination device  51  is disposed downstream from the sheet separation device  1  in the sheet conveyance direction, that is, the downstream side in the forward direction and the left side in  FIG. 1 . The sheet lamination device  51  includes a plurality of heat-pressure roller pairs  51   a ,  51   b , and  51   c  aligned along the sheet conveyance direction (see  FIGS. 9A to 10C ). Each of the plurality of heat-pressure roller pairs  51   a ,  51   b , and  51   c  applies heat and pressure to the two-ply sheet PJ while conveying the two-ply sheet PJ in the forward direction in a state in which the inner sheet PM is inserted in the two-ply sheet PJ. Further, a fourth sheet conveyance passage K 6  that functions as a sheet conveyance passage is disposed between the third conveyance roller pair  6  and the sheet lamination device  51 . 
     The first ejection tray  13  functions as an ejection tray on which the two-ply sheet PJ (and the inner sheet PM) is stacked when the two-ply sheet PJ is ejected after the sheet laminator  50  has performed the sheet laminating operation on the two-ply sheet PJ. 
     The second ejection tray  55  functions as an ejection tray on which a sheet on which the sheet laminator  50  does not perform the sheet laminating operation is stacked. Note that the second ejection tray  55  also functions as a retract portion onto which a subsequent two-ply sheet is temporarily purged (ejected), when the sheet laminator  50  performs the sheet laminating operation consecutively. The detailed description of the second ejection tray  55  functioning as a retract portion is given below, with reference to  FIGS. 9A to 10C . 
     The sheet laminator  50  further includes a plurality of sheet conveyance passages such as a first sheet conveyance passage K 1 , a second sheet conveyance passage K 2 , a third sheet conveyance passage K 3 , a first branched sheet conveyance passage K 4 , a second branched sheet conveyance passage K 5 , a fourth sheet conveyance passage K 6 , and a retract sheet conveyance passage K 7 . Each of the first sheet conveyance passage K 1 , the second sheet conveyance passage K 2 , the third sheet conveyance passage K 3 , the first branched sheet conveyance passage K 4 , the second branched sheet conveyance passage K 5 , the fourth sheet conveyance passage K 6 , and the retract sheet conveyance passage K 7  extends from the sheet separation device  1  to the sheet lamination device  51  and includes two conveyance guides (guide plates) facing each other to guide and convey the sheet such as the two-ply sheet PJ and the inner sheet PM. 
     In particular, in the present embodiment, the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  branch off in different directions from the third sheet conveyance passage K 3 . The first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  are disposed opposite across the third sheet conveyance passage K 3 , between the winding roller  20  and the third sheet conveyance passage K 3 . 
     Further, the fourth sheet conveyance passage K 6  is a sheet conveyance passage extending from (the third conveyance roller pair  6  of) the sheet separation device  1  to the sheet lamination device  51 . Further, the retract sheet conveyance passage K 7  is a sheet conveyance passage extending from (the sheet lamination device  51  of) the sheet separation device  1  to the second ejection tray  55  (retract portion). To be more specific, the fourth sheet conveyance passage K 6  and the retreat sheet conveyance passage K 7  branch off in different directions from the downstream side (that is, the left side in  FIG. 1 ) of the third conveyance roller pair  6 . 
     As illustrated in  FIG. 1 , for example, the two-ply sheet PJ is loaded on the first feed tray  11 . The first feed roller  2  feeds the uppermost two-ply sheet PJ on the first feed tray  11 , to the first conveyance roller pair  4 , and the first conveyance roller pair  4  conveys the two-ply sheet PJ along the first sheet conveyance passage K 1 . 
     Each of the first feed tray  11  and the first feed roller  2  functions as a first sheet feeder to feed the two-ply sheet PJ. The first sheet feeder is controlled by the controller  500 . To be more specific, the controller  500  drives and rotates the first feed roller  2  to feed the two-ply sheet PJ from the first feed tray  11 . 
     Further, the inner sheet PM is loaded on the second feed tray  12 . Then, the second feed roller  3  feeds the uppermost two-ply sheet PJ on the second feed tray  12 . 
     As described above, each of the second feed tray  12  and the second feed roller  3  functions as a second sheet feeder to feed the inner sheet PM that is a sheet to be inserted between the two sheets, which are the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ with the non-bonding portion being separated. Then, the controller causes the second feed roller  3  to drive and rotate as a second sheet feeder, so as to feed the inner sheet PM from the second feed tray  12  as a second sheet feeder. 
     Then, in the sheet laminator  50  according to the present embodiment, the controller  500  causes the second feed roller  3  (second sheet feeder) to start feeding the inner sheet PM from the second feed tray  12  (second sheet feeder) after the first feed roller  2  (first sheet feeder) has fed the two-ply sheet PJ from the first feed tray  11  (first sheet feeder) and before the operation to separate the non-bonding portion of the two-ply sheet PJ is completed. 
     That is, in the present embodiment, the feeding of the two-ply sheet PJ and the feeding of the inner sheet PM are not performed separately (operated by a user via the operation display panel  49 ) but are performed in a single operation. To be more specific, as a user presses the button on the operation display panel  49  once to start the operation, the sheet separating operation in which the two-ply sheet PJ is fed and separated, the sheet inserting operation in which the inner sheet PM is inserted into the two-ply sheet PJ between the first sheet P 1  and the second sheet P 2  separated from each other, and the sheet laminating operation are collectively performed automatically based on the single instruction. 
     The operation to start feeding the inner sheet PM from the second feed tray  12  is performed not after completion of the sheet separating operation of the two-ply sheet PJ but performed before completion of the sheet separating operation of the two-ply sheet PJ. Therefore, the time required for a series of steps from when the two-ply sheet PJ is fed from the first feed tray  11  to when the inner sheet PM is completely inserted in the two-ply sheet PJ is reduced efficiently, and therefore the productivity of the sheet separation device  1  is enhanced. That is, the time required for the operation from the start to the end performed by the sheet laminator  50  is reduced. 
     Each of the first conveyance roller pair  4 , the second conveyance roller pair  5 , the third conveyance roller pair  6 , a first ejection roller pair  7 , and a second ejection roller pair  8  includes a drive roller and a driven roller and conveys the sheet nipped by the respective nip regions. The third sheet conveyance passage K 3  includes the second conveyance roller pair  5 , the winding roller  20 , and the third conveyance roller pair  6  in this order from upstream to downstream in the sheet conveyance direction. In particular, the winding roller  20 , the third conveyance roller pair  6 , and the second ejection roller pair  8  are configured to be rotatable in a forward direction or in a reverse direction. The third conveyance roller pair  6  and the second ejection roller pair  8  convey the sheet in the forward direction that is the left direction in  FIG. 1  and in the reverse direction that is the right direction in  FIG. 1 . The third conveyance roller pair  6  also functions as a sheet conveying roller pair that conveys the sheet to the sheet lamination device  51  or to the second ejection tray  55 . The first ejection roller pair  7  functions as a sheet conveying roller pair that conveys and ejects the two-ply sheet PJ (and the inner sheet PM) after the sheet laminating operation, toward the first ejection tray  13 . 
     Note that a switching claw  17  is disposed downstream from the third conveyance roller pair  6  in the forward direction (sheet conveyance direction to the left in  FIG. 1 ). The switching claw  17  that functions as a switcher switches the direction of conveyance of the sheet P, for example, by conveying the sheet P toward the sheet lamination device  51  or toward the second ejection tray  55 . 
     That is, the switching claw  17  functions as a switcher that switches a first state and a second state. The first state is a state in which the fourth sheet conveyance passage K 6  is open and the retract sheet conveyance passage K 7  is closed, which is the state illustrated in  FIG. 9A , for example. The second state is a state in which the fourth sheet conveyance passage K 6  is closed and the retract sheet conveyance passage K 7  is open, which is the state illustrated in  FIG. 9C , for example. 
     The switching claw  17  is controlled according to the mode selected by a user (in particular, when the sheet laminating operation is consecutively performed on the plurality of two-ply sheets PJ), so as to switch the direction of conveyance (ejection) of the sheet P. 
     A detailed description is given below of the operations of the switching claw  17  functioning as a switcher, with reference to  FIGS. 9A to 9D  and  FIGS. 10A to 10C , for example. 
     Referring to  FIG. 1 , each of the first sensor  41 , the second sensor  42 , the third sensor  43 , the fourth sensor  44 , and the fifth sensor  45 , the seventh sensor  47 , and the eighth sensor  48  functions as a sheet detector employing a reflective photosensor that optically detects whether the sheet is present at the position of each sensor. The first sensor  41  is disposed near a portion downstream from the first conveyance roller pair  4  in the sheet conveyance direction. The second sensor  42  is disposed near a portion downstream from the second feed roller  3  in the sheet conveyance direction. The third sensor  43  is disposed near a portion downstream from the second conveyance roller pair  5  in the sheet conveyance direction. The fourth sensor  44  is disposed near a portion downstream from the winding roller  20  (at the left side of the winding roller  20  in  FIG. 1 ) and upstream from the third conveyance roller pair  6  (at the right side of the third conveyance roller pair  6  in  FIG. 1 ) in the sheet conveyance direction. The fifth sensor  45  is disposed downstream from the fourth sheet conveyance passage K 6  from the sheet separation device  1  to the sheet lamination device  51  (at the left side of the third conveyance roller pair  6  in  FIG. 1 ) in the sheet conveyance direction. Further, the seventh sensor  47  is disposed on the first branched sheet conveyance passage K 4 . The eighth sensor  48  is disposed on the second branched sheet conveyance passage K 5 . 
     Note that the sixth sensor  46  functions as an abnormality detector that detects an abnormal state while the sheet separating operation is performed. The detailed description of the sixth sensor  46  is given below. 
     A description is given of the winding roller  20 , with reference to  FIGS. 2A, 2B, 3A, 3B, 5B to 5D, and 6A . 
     The winding roller  20  is a roller that winds the two-ply sheet PJ, with a gripper  32  that is one example of a gripper (handle) grips a gripped portion B of the two-ply sheet PJ at a winding start position W (see  FIG. 5B ). The gripped portion B is an end of the two-ply sheet PJ that is opposite an end at which the bonding portion A is formed, which is referred to as the other end of the two-ply sheet PJ. While the gripper  32  grips the gripped portion B of the two-ply sheet PJ, the winding roller  20  rotates in a predetermined rotation direction (that is, the counterclockwise direction in  FIGS. 5A to 5D ) to wrap the two-ply sheet PJ around the winding roller  20 . The winding roller  20  is rotatable about a rotary shaft  20   a  in the forward direction and in the reverse direction. The controller  500  controls a drive motor that drives the winding roller  20 . 
     To be more specific, the two-ply sheet PJ is fed from the first feed tray  11 , passes through the first sheet conveyance passage K 1 , and is conveyed by the second conveyance roller pair  5  in the forward direction along the third sheet conveyance passage K 3 . The two-ply sheet PJ passes through the winding start position W of the winding roller  20  once and is conveyed to a position of the third conveyance roller pair  6  that is a position at which the trailing end of the two-ply sheet PJ passes through the fourth sensor  44  but does not pass through the third conveyance roller pair  6 , that is, the position before the third conveyance roller pair  6 . Thereafter, the third conveyance roller pair  6  rotates in the reverse direction to convey the two-ply sheet PJ in the reverse direction to the position of the winding roller  20  that is the winding start position W, and the gripper  32  grips the other end (leading end) of the two-ply sheet PJ. The two-ply sheet PJ is further conveyed in a state in which the other end (leading end) of the two-ply sheet PJ is gripped by the gripper  32 , and the winding roller  20  rotates in the counterclockwise direction in  FIG. 1  to wind the two-ply sheet PJ around the winding roller  20 . 
     With reference to  FIG. 5C ′, when the two-ply sheet PJ is wound around the winding roller  20 , the length of a sheet wound around the winding roller  20  is proportional to the diameter of the winding roller  20 . Therefore, since a first sheet P 1  is on the inner side to the center of the winding roller  20 , that is, closer to the inner circumferential surface of the winding roller  20 , than a second sheet P 2  on the outer side to the center of the winding roller  20 , that is, closer to the outer circumferential surface of the winding roller  20 , the length of the first sheet P 1  wound around the winding roller  20  is shorter than the length of the second sheet P 2  wound around the winding roller  20 . As a result, misalignment occurs in a part of the two-ply sheet PJ in which the sheet P 1  is in close contact with the sheet P 2  (in other words, the part in which the sheet P 1  sticks to the sheet P 2 ) other than the bonding portion A and the gripped portion B. The misalignment causes the first sheet P 1  to slack and bend toward the second sheet P 2 , forming a gap C between the two sheets, which are the first sheet P 1  and the second sheet P 2 , in the vicinity of the bonding portion A of the two-ply sheet PJ, as illustrated in  FIGS. 5D and 6A . In other words, when the first sheet P 1  that is placed on the second sheet P 2  is warped upward, the gap C is formed between the first sheet P 1  and the second sheet P 2  at one end of the two-ply sheet PJ, that is, the upstream side in the sheet conveyance direction when the two-ply sheet PJ is conveyed in the right direction in  FIG. 1 . As described above, the two sheets P 1  and P 2  that are in close contact with each other without any gap are separated from each other. 
     Particularly in the present embodiment, in order to significantly form the gap C as described above, that is, in order to increase the difference between the length of the first sheet P 1  wound around the winding roller  20  and the length of the second sheet P 2  wound around the winding roller  20 , the two-ply sheet PJ is wound around the winding roller  20  at least one round. 
     As described above, in the present embodiment, by providing the winding roller  20  to wind the two-ply sheet PJ around the rotary shaft  20   a , the two-ply sheet PJ is separatable without increasing the size and cost of the sheet laminator  50 . 
     As illustrated in  FIG. 5B ′, the gripper  32  in the present embodiment is configured to grip the gripped portion B of the two-ply sheet PJ without contacting the end surface of the other end of the gripped portion B of the two-ply sheet PJ. 
     Specifically, the gripper  32  is configured to sandwich and grip the gripped portion B of the two-ply sheet PJ between the gripper  32  and a receiving portion  20   b  of the winding roller  20  without causing any member to abut and restrict the end surface of the other end of the two-ply sheet PJ, in other words, without causing any member to hit or contact the end surface of the two-ply sheet PJ. The receiving portion  20   b  of the winding roller  20  is a part of the outer circumferential portion of the winding roller  20  and is arranged to be exposed outwardly and facing the gripper  32 . 
     To be more specific, the two-ply sheet PJ is not nipped and gripped by the gripper  32  and the receiving portion  20   b  of the winding roller  20  in a state in which a specific member such as the gripper  32  contacts the end surface of the other end (that is the leading end face). The two-ply sheet PJ is nipped and gripped by the gripper  32  and the receiving portion  20   b  while the end surface of the other end (leading end face) does not contact any member. In this state, the gripper is located close to the second sheet P 2  on the outer side to the center of the winding roller  20  and the receiving portion  20   b  is located close to the first sheet P 1  on the inner side to the center of the winding roller  20 . 
     Therefore, when compared with a configuration in which the leading end face of the two-ply sheet PJ contacts a member, the above-described structure according to the present embodiment reduces damage on the two-ply sheet PJ (particularly, the leading end). In particular, once the leading end face of the two-ply sheet PJ is damaged, it is difficult to perform the sheet laminating operation on the damaged leading end face. Therefore, the configuration of the present disclosure is useful. 
     Note that, in the present embodiment, the bonding portion A of the two-ply sheet PJ wound around the winding roller  20  is the one end of the two-ply sheet PJ. The one end is opposite to the other end functioning as the gripped portion B. 
     In the present embodiment, at least one of the gripper  32  (handle) and the receiving portion  20   b  is made of elastic material such as rubber. 
     According to this configuration, when compared with a sheet separation device having a configuration in which the gripper  32  and the receiving portion  20   b  have rigid bodies made of metal or resin, the above-described sheet separation device  1  according to the present embodiment enhances the gripping force to grip the two-ply sheet PJ and prevents the surfaces of the two-ply sheet PJ from being damaged. In particular, the sheet separation device  1  including the gripper  32  and the receiving portion  20   b  made of the elastic material easily exhibits the above-described effect. 
     As illustrated in  FIGS. 2A, 2B, 3A, and 3B , the moving mechanism  30  moves the gripper  32  between a gripping position (a position illustrated in  FIGS. 2A and 3A ) at which the gripper  32  can grip the two-ply sheet PJ and a releasing position (a position illustrated in  FIGS. 2B and 3B ) at which the gripper  32  is released from the gripping position. 
     To be more specific, the moving mechanism  30  includes an arm  31 , a compression spring  33 , a cam  34 , and a motor. The compression spring  33  functions as a biasing member. The motor drives to rotate the cam  34  in the forward direction or the reverse direction. 
     The arm  31  holds the gripper  32 . The arm  31  and the gripper  32  are held together by the winding roller  20  to be rotatable together about a support shaft  31   a . In the present embodiment, the gripper  32  is connected to the tip of the arm  31 , and the gripper  32  and the arm  31  are made (held) as a single unit. Alternatively, the gripper  32  and the arm  31  may be made as separate members, and the gripper  32  may be mounted on the arm  31 , that is, may be held by the arm  31 . In any case, the arm  31  holding the gripper  32  rotates about the rotary shaft  20   a  together with the winding roller  20 . 
     The compression spring  33  functions as a biasing member that biases the arm  31  so that the gripper  32  moves from the releasing position illustrated in  FIG. 2B  to the gripping position illustrated in  FIG. 2A . To be more specific, one end of the compression spring  33  is connected to a fixed position near the rotary shaft  20   a , and the other end of the compression spring  33  is connected to one end of the arm  31  that is an end opposite to the other end of the arm  31  connected to the gripper  32  with respect to the support shaft  31   a.    
     The cam  34  pushes the arm  31  against the biasing force of the compression spring  33  that functions as the biasing member, so that the gripper  32  moves from the gripping position illustrated in  FIG. 2A  to the releasing position illustrated in  FIG. 2B . The motor controlled by the controller  500  drives the cam  34  to rotate in the forward direction or the reverse direction at a desired rotation angle. The cam  34  is held by the apparatus housing so as to be rotatable about a cam shaft  34   a  separately from the winding roller  20 . 
     In the moving mechanism  30  configured as described above, as illustrated in  FIGS. 2A and 3A , in a state in which the cam  34  is not in contact with the arm  31 , the arm  31  is biased by the compression spring  33  to press the gripper  32  against the receiving portion  20   b . This state is referred to as a closed state. In the closed state, the gripper  32  and the receiving portion  20   b  grip the two-ply sheet PJ. 
     By contrast, as illustrated in  FIGS. 2B and 3B , in a state in which the cam  34  is contacts and presses the arm  31 , the arm  31  rotates in the counterclockwise direction in  FIG. 2B  about the support shaft  31   a  against the biasing force of the compression spring  33 , so that the gripper  32  separates from the receiving portion  20   b . This state is referred to as an open state. In the open state, the two-ply sheet PJ is not gripped, which is referred to as a grip release state. 
     Note that, in the present embodiment, as illustrated in  FIGS. 3A and 3B , the winding roller  20  includes a plurality of roller portions (i.e., seven roller portions in the present embodiment) separated in the axial direction of the winding roller  20 . Similarly, the cam  34  includes a plurality of cam portions separated in the axial direction of the cam  34  so that the divided positions of the plurality of cam portions of the cam  34  respectively meet and face the plurality of roller portions of the winding roller  20 . 
     Setting portions separated in the axial direction to grip the two-ply sheet PJ as described above, that is, not setting the entire area of the winding roller  20  and the cam  34  in the axial direction to grip the two-ply sheet PJ share load to grip the two-ply sheet PJ. The above-described configuration is useful when a gripping force required to grip the two-play sheet PJ increases. 
     Here, a description is given of the fourth sensor  44  in the sheet laminator  50  according to the present embodiment, with reference to  FIGS. 1, 4D, and 5A . 
     The fourth sensor  44  functions as a sheet detector to detect the two-ply sheet PJ conveyed between the winding roller  20  and the third conveyance roller pair  6 . The fourth sensor  44  detects the leading end of the two-ply sheet PJ conveyed to the winding roller  20  in the sheet conveyance direction by the third conveyance roller pair  6 . Based on the detection results detected by the fourth sensor  44 , the controller  500  controls the moving mechanism  30 . 
     To be more specific, the fourth sensor  44  is disposed in the sheet conveyance passage between the winding roller  20  and the third conveyance roller pair  6 . As illustrated in  FIGS. 4D and 5A , when the third conveyance roller pair  6  conveys the two-ply sheet PJ in the reverse direction toward the position of the winding roller  20  with the gripped portion B of the two-ply sheet PJ being the leading end, the fourth sensor  44  detects the leading end (that is, the tip of one end of the gripped portion B) of the two-ply sheet PJ conveyed in the reverse direction. In response to the detection timing at which the fourth sensor  44  detects the leading end (in the reverse direction) of one end of the gripped portion B, the controller  500  adjusts and controls a timing to stop the two-ply sheet PJ at the gripping position and a timing at which the gripper  32  grips the gripped portion B. Specifically, after a predetermined time has passed since the fourth sensor  44  detected the front end of the two-ply sheet PJ, the third conveyance roller pair  6  stops the reverse direction conveyance of the two-ply sheet PJ, and the cam  34  rotates to pivot the arm  31  of the moving mechanism  30  so that the gripper  32  moves from the releasing position illustrated in  FIG. 2B  to the gripping position illustrated in  FIG. 2A . 
     The above-described control accurately performs an operation in which the end surface of the two-ply sheet PJ is nipped by the gripper  32  and the receiving portion  20   b  without contacting (abutting) the end surface of the two-ply sheet PJ on any member. 
     As described above, the third conveyance roller pair  6  is a sheet conveying roller pair that conveys the two-ply sheet PJ with the other end (i.e., the gripped portion B) as a leading end, toward the winding start position W of the winding roller  20  in the third sheet conveyance passage K 3  (sheet conveyance passage) between the third conveyance roller pair  6  and the winding roller  20 . 
     Now, a description is given of the separation claws  16  each functioning as a separator, with reference to  FIGS. 6A to 6C, 11, 12A to 12E, and 15 . 
     Each of the separation claws  16  is a claw-shaped member that moves from the standby position illustrated in  FIG. 12A  and is inserted into the gap C formed between the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ at a predetermined position of the two-ply sheet PJ. 
     To be more specific, the separation claws  16  are inserted into the gap C formed between the first sheet P 1  and the second sheet P 2  at a position between the winding roller  20  and the third conveyance roller pair  6  from the standby positions outside both ends of the two-ply sheet PJ in the width direction of the two-ply sheet PJ in a state in which the other end (that is the gripped portion B) is wound by the winding roller  20  and the one end (that is the bonding portion A) is nipped by the third conveyance roller pair  6 . 
     More specifically, in the present embodiment, the separation claws  16  are a pair of separation claws that functions as a pair of separators disposed at both sides of the two-ply sheet PJ in the width direction that is the direction perpendicular to a plane on which  FIGS. 6A to 6C  are illustrated and the horizontal direction in  FIGS. 11 and 15 . As illustrated in  FIGS. 12A to 12E , the vertical length of each of the separation claws  16  in the vertical direction (thickness direction) of the two-ply sheet PJ gradually increases from the tip of each of the separation claws  16  near the center in the width direction of the two-ply sheet PJ, to the rear end of the separation claw  16  near the outsides in the width direction of the two-ply sheet PJ. Further, the separation claws  16  are movable in the width direction of the two-ply sheet PJ by a driving device  76  (see  FIG. 15 ) controlled by the controller  500 . 
     The separation claws  16  configured as described above ordinarily stand by at respective standby positions at which the separation claws  16  do not interfere with conveyance of the sheet such as the two-ply sheet PJ in the third sheet conveyance passage K 3 . As illustrated in  FIG. 12A , the standby positions of the separation claws  16  are outside of the two-ply sheet PJ (including the first sheet P 1  and the second sheet P 2 ) in the width direction of the two-ply sheet PJ. Subsequently, as illustrated in  FIGS. 11 and 12B , the separation claws  16  enter the gap C in the two-ply sheet PJ when separating the two-ply sheet PJ (including the first sheet P 1  and the second sheet P 2 ). As a result, the separation claws  16  secure the gap C to be relatively large. 
     As illustrated in  FIG. 15 , the driving device  76  that moves the pair of separation claws  16  in the width direction includes a motor  77 , a gear pulley  78 , a pulley  79 , and a timing belt  80 . The gear pulley  78  has a step-like ring shape including a gear and a pulley. The gear meshes with a motor gear mounted on a motor shaft of the motor  77 . The pulley stretches and supports the timing belt  80  together with the pulley  79 . One separation claw  16  of the pair of separation claws  16  includes a fixed portion  16   a  that is fixed to a part of the belt surface of the timing belt  80  that is the upper side of the belt surface in  FIG. 15 . The other separation claw  16  includes a fixed portion  16   a  that is fixed to a part of the other belt surface of the timing belt  80  that is the lower side of the belt surface in  FIG. 15 . 
     In the driving device  76  as configured described above, the motor  77  drives to rotate the motor shaft in a direction indicated by arrow in  FIG. 15  (i.e. clockwise direction), the gear pulley  78  rotates counterclockwise, the timing belt  80  rotates in the counterclockwise direction, and the pair of separation claws  16  moves from the outside in the width direction of the two-ply sheet PJ to the center in the width direction of the two-ply sheet PJ (that is, the pair of separation claws  16  approaches each other). In contrast, when the motor  77  drives to rotate the motor shaft in the direction opposite to the arrow direction in  FIG. 15 , the pair of separation claws  16  moves from the center in the width direction of the two-ply sheet PJ toward the outside in the width direction of the two-ply sheet PJ (that is, the pair of the separation claws  16  moves in a direction away from each other). 
     In a state in which the separation claws  16  are inserted into the gap C in the two-ply sheet PJ, the separation claws  16  relatively move from the one end of the two-ply sheet PJ near the bonding portion A to the other end of the two-ply sheet PJ near the gripped portion B. Then, the separation claws  16  move in the width direction between the first sheet P 1  and the second sheet P 2  at the other end of the two-ply sheet PJ. 
     Specifically, the controller  500  controls the driving device  76  (see  FIG. 15 ) to move the pair of separation claws  16  as follows. As illustrated in  FIGS. 11B and 11C , the pair of separation claws  16  is inserted into both ends of the gap C in the two-ply sheet PJ in the width direction and relatively moves to the other end of the two-ply sheet PJ that is the gripped portion B. After the pair of separation claws  16  has relatively moved to the other end of the two-ply sheet PJ, as illustrated in  FIG. 12D , the pair of separation claws  16  on the other end of the two-ply sheet PJ moves in the width direction from both ends of the two-ply sheet PJ to the center of the two-ply sheet PJ between the first sheet P 1  and the second sheet P 2 . In order to cause the pair of separation claws  16  to move as described above, the driving device  76  is configured so that the pair of separation claws  16  moves from the standby positions to the positions at which the separation claws  16  come close to each other. 
     The above-described mechanism, which includes the winding roller  20  to wind the two-ply sheet PJ and the separation claws  16  to be inserted into the two-ply sheet PJ so as to separate the two-ply sheet PJ, reduces the size of the sheet separation device  1 , when compared with a mechanism using a large-scale device such as a vacuum device to separate the two-ply sheet PJ. That is, without increasing the size of the sheet laminator  50 , the above-described mechanism reliably separates the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ. 
     In particular, since the separation claws  16  in the present embodiment move over substantially the entire area in the width direction of the two-ply sheet PJ on the other end of the two-ply sheet PJ (that is the trailing end of the two-ply sheet PJ), the separation claws  16  sufficiently separate (in other words, peel) the other ends of the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ that is opposite the bonding portion A. Therefore, it is less likely that the above-described configuration causes an inconvenience that the other end of the two-ply sheet PJ that is opposite the bonding portion A is not sufficiently separated and that the inner sheet PM (see  FIG. 12E ) would not be inserted into the other end of the two-ply sheet PJ from the other end of the two-ply sheet PJ. Additionally, the above-described configuration allows the separation claws  16  to easily function as a switcher, that is, to separately guide the first sheet P 1  and the second sheet P 2  to the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5 , respectively. 
     Here, a description is given of the separation claws  16  that functions as a switcher, with reference to  FIGS. 7A to 10E . 
     In the present embodiment, the separation claws  16  that functions as a separator also function as a switcher that guides the first sheet P 1  and the second sheet P 2  separated by the separation claws  16 , to the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  branching off in different directions, respectively (see  FIG. 7C ). 
     To be more specific, as illustrated in  FIG. 7C , the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  branch off in different directions from the third sheet conveyance passage K 3  between the winding roller  20  and each of the separation claws  16  (separator). To be more specific, the first branched sheet conveyance passage K 4  branches upward from the third sheet conveyance passage K 3 , and the second branched sheet conveyance passage K 5  branches downward from the third sheet conveyance passage K 3 . 
     As illustrated in  FIGS. 7A to 7C , after the separation claws  16  are inserted into the gap C, the third conveyance roller pair  6  conveys the one end of the two-ply sheet PJ to the left side in  FIGS. 7A to 7C  so that the winding of the other end of the two-ply sheet PJ on the winding roller  20  is released (see  FIG. 12A  to  FIG. 12C ). After the winding of the other end of the two-ply sheet PJ on the winding roller  20  is released, the separation claws  16  move to the center in the width direction of the two-ply sheet PJ as illustrated in  FIG. 12D , and stop at the center in the width direction of the two-ply sheet PJ. Then, while the separation claws  16  remain in the above-described state, the third conveyance roller pair  6  conveys the other end of the two-ply sheet PJ to the right side in  FIGS. 7A to 7C  again. Thereafter, the separation claws  16  guide the first sheet P 1  and the second sheet P 2  separated by the separation claws  16 , to the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5 , respectively. That is, the first sheet P 1  is guided to the first branched sheet conveyance passage K 4 , and the second sheet P 2  is guided to the second branched sheet conveyance passage K 5 . Subsequently, as illustrated in  FIGS. 8A to 8C and 12E , the separation claws  16  move to the standby positions, and the second conveyance roller pair  5  conveys the inner sheet PM to the one end of the third sheet conveyance passage K 3 , that is, the right side in  FIGS. 8A to 8C , to insert the inner sheet PM between the first sheet P 1  and the second sheet P 2  separated from the two-ply sheet PJ. 
     As described above, each of the separation claws  16  in the present embodiment functions as a separator that separates (in other words, peels) the non-bonding portion of the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ, and also functions as a switcher that separately guides the separated two sheets, which are the first sheet P 1  and the second sheet P 2 , to the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5 , respectively. Accordingly, the above-described configuration reduces the size and cost of the sheet laminator  50 , when compared with the configuration of a sheet separation device including the separator and the switcher as different units. That is, the above-described configuration efficiently and reliably separates the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ. 
     The seventh sensor  47  optically detects a state in which the first sheet P 1  separated apart from the second sheet P 2  is successfully conveyed to the first branched sheet conveyance passage K 4 . Further, the eighth sensor  48  optically detects a state in which the second sheet P 2  separated apart from the first sheet P 1  is successfully conveyed to the second branched sheet conveyance passage K 5 . 
     Note that each separation claw  16  in the present embodiment functions as both a separator and a switcher. However, the sheet separation device  1  according to the present embodiment may further include a member that functions as a switcher, different from the separation claw  16  that functions as a separator. 
     Here, a description is given of a first guide  25  provided in the sheet separation device  1  according to the present embodiment, with reference, for example,  FIGS. 6A to 7C . 
     The first guide  25  is disposed between the separation claws  16  and the winding roller  20  in the third sheet conveyance passage K 3 . The first guide  25  functions as a limiter to limit an amount of slack (in other words, a deflection amount) of the first sheet P 1  that is wound around the winding roller  20  on the inner side of the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ wound around the winding roller  20 . 
     To be more specific, the first guide  25  that functions as a limiter is a conveyance guide disposed on the side in which the winding roller  20  is disposed with respect to an imaginary plane S 1 , that is, above the imaginary plane S 1  in  FIG. 6A , in the third sheet conveyance passage K 3 . The imaginary plane S 1  (see  FIG. 6A ) is an imaginary plane passing through the winding start position W of the winding roller  20  and the nip region of the third conveyance roller pair  6  in the third sheet conveyance passage K 3 . The first guide  25  has a shape like substantially a triangular prism having a plane along the outer circumferential surface of the winding roller  20 , and the plane covers a part of the outer circumferential surface of the winding roller  20  and is separated from the winding roller  20  by a predetermined gap. The first guide  25  functions as a conveyance guide of the third sheet conveyance passage K 3  and a conveyance guide of the first branched sheet conveyance passage K 4 . That is, the first guide  25  guides the sheet conveyed through the third sheet conveyance passage K 3 , the sheet conveyed through the first branched sheet conveyance passage K 4 , and the sheet wound around the winding roller  20 . 
     In particular, in the third sheet conveyance passage K 3 , the first guide  25  limits bending the two-ply sheet PJ upward (in particular, bending the first sheet P 1  upward) between the winding roller  20  and the third conveyance roller pair  6 . Therefore, the gap C in the two-ply sheet PJ that is mainly formed by bending the first sheet P 1  upward is intensively formed between the first guide  25  and the third conveyance roller pair  6 . Accordingly, the above-described configuration increases the size of the gap C even if the winding amount of the two-ply sheet PJ wound around the winding roller  20  is not large, and the separation claws  16  smoothly enter the gap C to separate the two-ply sheet PJ. 
     Now, a description is given of a second guide  26  provided in the sheet separation device  1  according to the present embodiment, with reference to  FIGS. 6A to 7C . 
     The second guide  26  is disposed between the separation claws  16  and the winding roller  20  in the third sheet conveyance passage K 3 . The second guide  26  functions as a guide to guide the second sheet P 2  that is an outer sheet of the two sheets P 1  and P 2  of the two-ply sheet PJ wound around the winding roller  20 . 
     To be more specific, the second guide  26  that functions as a guide is a sheet conveyance guide disposed on the side in which the winding roller  20  is not disposed with respect to the imaginary plane S 1 , that is, below the imaginary plane S 1  in  FIG. 6A , in the third sheet conveyance passage K 3 . The second guide  26  is disposed to face the lower surface of the sheet from a portion close and upstream from the second conveyance roller pair  5  in the forward direction to a portion downstream from the third conveyance roller pair  6  in the forward direction. That is, the second guide  26  guides the sheet conveyed on the third sheet conveyance passage K 3 . 
     In particular, in the third sheet conveyance passage K 3  between the winding roller  20  and the third conveyance roller pair  6 , a clearance between the first guide  25  and the second guide  26  is set to be a value by which the sheet having the largest thickness is conveyed. Since this setting limits a gap between the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ so as not to be too large between the first guide  25  and the second guide  26 , the gap C in the two-ply sheet PJ that is mainly formed by bending the first sheet P 1  upward is intensively formed. Accordingly, the separation claws  16  smoothly enter the gap C to separate the two-ply sheet PJ. 
     Here, a description is given of the sixth sensor  46 , with reference to  FIGS. 6A to 7C . The sixth sensor  46  functions as an abnormality detection sensor or an abnormality detector to detect an abnormal state in which the gap C formed between the first sheet P 1  and the second sheet P 2  at a predetermined position (that is, a position between the third conveyance roller pair  6  and the winding roller  20 ) is not larger than a predetermined size before the separation claws  16  move from the standby positions, to be more specific, before the separation claws  16  move from the standby positions illustrated in  FIG. 15  to the separation positions illustrated in  FIGS. 11 and 12A . The predetermined size is the size of the gap C into which the separation claws  16  enter, which is determined by experiments. That is, the sixth sensor  46  that functions as the abnormality detector detects the abnormal state in which the gap C formed between the first sheet P 1  and the second sheet P 2  at a predetermined position is not larger than the predetermined size before the separation claws  16  are inserted into the gap C. 
     In other words, at a timing at which the gap C is formed between the first sheet P 1  and the second sheet P 2 , as illustrated in  FIGS. 5D, 6A, and 6C , the sixth sensor  46  that functions as the abnormality detector detects the abnormal state such as a state in which the gap is not formed at all or a state in which the gap is not formed as a sufficient gap C. 
     In the present embodiment, the controller  500  notifies occurrence of an abnormal state when the abnormal state is detected by the sixth sensor  46  (abnormality detector). To be more specific, as illustrated in  FIG. 1 , the sheet laminator  50  includes an operation display panel  49  that functions as an operation display device on the exterior of the sheet laminator  50  to display various kinds of information about the sheet laminator  50  and input various kinds of commands. When the controller  500  determines the abnormal state based on the results detected by the sixth sensor  46 , that is, when the two-ply sheet PJ does not have the sufficiently large gap C, the controller  500  controls the operation display panel  49  to display that the abnormal state is detected. For example, the operation display panel  49  displays “Since an abnormality has occurred, the process of inserting the inner sheet is stopped. Please check the setting direction of the two-ply sheet in the unit sheet feed tray. If the setting direction is correct and similar abnormalities are repeated, please contact a service person.” 
     The above-described sixth sensor  46  that functions as the abnormality detector may be, for example, a lever type sensor that comes into contact with the upper first sheet P 1  of the two-ply sheet PJ forming the gap C larger than the predetermined size. 
     Here, a description is given or the sheet laminating operation on a plurality of two-ply sheets in the sheet laminator  50  according to the present embodiment, with respect to  FIGS. 9A to 10C . 
     As illustrated in  FIGS. 9A to 10C , in a case in which the sheet laminator  50  performs the sheet laminating operation on a plurality of two-ply sheets PJ including a preceding two-ply sheet PJ 1  and a subsequent two-ply sheet PJ 2 , when the sheet lamination device  51  is performing the sheet laminating operation on the preceding two-ply sheet PJ 1 , the sheet separation device  1  that performs the sheet separating operation and the sheet inserting operation performs at least the sheet separating operation on the subsequent two-ply sheet PJ 2 . 
     That is, in the present embodiment, when continuously performing the sheet laminating operation on each of the plurality of two-ply sheets PJ (i.e., the preceding two-ply sheet PJ 1  and the subsequent two-ply sheet PJ 2 ), the sheet laminator  50  according to the present embodiment does not start the sheet separating operation on the subsequent two-ply sheet PJ 2  after completely finishing the sheet laminating operation on the preceding two-ply sheet PJ 1  but starts the sheet separating operation on the subsequent two-ply sheet PJ 2  while the sheet lamination device  51  is performing the sheet laminating operation on the preceding two-ply sheet PJ 1 . This sheet laminating operation continuously performed on the plurality of two-ply sheets may hereinafter be referred to as a continuous sheet laminating operation. Further, in other words, the sheet laminator  50  according to the present embodiment narrows the gap (space) between the preceding two-ply sheet PJ 1  and the subsequent two-ply sheet PJ 2  in the sheet conveyance direction to perform the continuous sheet laminating operation. 
     Therefore, the time to finish the entire sheet laminating operation (series of jobs) on the plurality of two-ply sheets PJ is reduced, thereby enhancing the productivity of the sheet laminator  50 . 
     In particular, in the present embodiment, as illustrated in  FIGS. 9C, 9D, and 10A , when the sheet separation device  1  performs the sheet separating operation on the subsequent two-ply sheet PJ 2  in the continuous sheet laminating operation, the switching claw  17  that functions as a switcher is controlled to be in the second state in which the fourth sheet conveyance passage K 6  is closed and the retract sheet conveyance passage K 7  is open). 
     That is, when the sheet separation device  1  performs the sheet separating operation on the subsequent two-ply sheet PJ 2 , the fourth sheet conveyance passage K 6  is closed and, at the same time, the retract sheet conveyance passage K 7  is open. 
     Accordingly, when compared with a configuration in which the retract sheet conveyance passage K 7  is not provided and the continuous sheet laminating operation is performed by using the fourth sheet conveyance passage K 6  alone, even if the length of the fourth sheet conveyance passage K 6  (in the sheet conveyance direction) is shortened (that is, even if the size of the sheet laminator  50  is reduced), the configuration according to the present embodiment prevents the inconvenience in which the subsequent two-ply sheet PJ 2  interfere the preceding two-ply sheet PJ 1 . 
     Note that the control of changing the position of the switching claw  17  is performed by the fifth sensor  45  disposed proximate to the branching point of the fourth sheet conveyance passage K 6  and the retract sheet conveyance passage K 7 , in response to the timing that the trailing end of the preceding two-ply sheet PJ 1  is detected. 
     Further, as illustrated in  FIGS. 10A to 10C , the continuous sheet laminating operation in the present embodiment is controlled that the trailing end of the preceding two-ply sheet PJ 1  passes the extreme upstream portion of the sheet lamination device  51  (that is, the nip region formed between the rollers of a first heat-pressure roller pair  51   a  that is one of the plurality of heat-pressure roller pairs  51   a ,  51   b , and  51   c  and is an extreme-upstream heat-pressure roller pair disposed extreme upstream of the plurality of heat-pressure roller pairs  51   a ,  51   b , and  51   c  of the sheet lamination device  51  in the sheet conveyance direction), and then the leading end of the subsequent two-ply sheet PJ 2  enters the extreme upstream portion (i.e., the nip region of the first heat-pressure roller pair  51   a ). In other words, the controller  500  causes the leading end of the subsequent two-ply sheet PJ 2  to enter the extreme upstream portion of the sheet lamination device  51  in the sheet conveyance direction after the trailing end of the preceding two-ply sheet PJ 1  passed the extreme upstream portion of the sheet lamination device  51 . 
     Therefore, the continuous sheet laminating operation is performed in a state in which the gap (space) between the preceding two-ply sheet PJ 1  and the subsequent two-ply sheet PJ 2  is further reduced (narrowed). Accordingly, the time to finish the entire sheet laminating operation (series of jobs) on the plurality of two-ply sheets PJ is reduced, thereby enhancing the productivity of the sheet laminator  50 . 
     Now, a description is given of the operations performed in the sheet laminator  50  when the sheet laminating operation is performed continuously on the plurality of two-ply sheets PJ, with reference to  FIGS. 4A to 10C . 
     Further, in the description of the operations, the operations of the separation claws  16  are appropriately described with reference to  FIGS. 11 to 12E , and the control flow is described with reference to a flowchart of  FIG. 13  including  FIGS. 13A and 13B  and  FIG. 14 . 
     First, the first feed roller  2  and the first conveyance roller pair  4  start feeding the two-ply sheet PJ (that is a preceding two-ply sheet PJ 1 ) from the first feed tray  11  in step S 1  of  FIG. 13A . Then, as illustrated in  FIG. 4A , the second conveyance roller pair  5  conveys the two-ply sheet PJ with the bonding portion A as a leading end of the two-ply sheet PJ in the forward direction that is a direction from the right side to the left side in  FIGS. 4A to 4D  in the third sheet conveyance passage K 3 . 
     At this time, the controller  500  controls the moving mechanism  30  so that the gripper  32  is positioned at the gripping position. That is, the cam  34  moves to a rotational position at which the cam  34  does not press the arm  31 . When the gripper  32  is positioned at the gripping position as described above, the gripper  32  does not block conveyance of the sheet in the third sheet conveyance passage K 3 . The separation claws  16  stand by at the standby positions (illustrated in  FIG. 12A ) at which the separation claws  16  do not block conveyance of the sheet in the third sheet conveyance passage K 3 . 
     Then, as illustrated in  FIG. 4B , the controller  500  determines whether the third sensor  43  has detected the bonding portion A of the two-ply sheet PJ (that is the leading end of the two-ply sheet PJ conveyed in the forward direction, in other words, the one end of the two-ply sheet PJ), in step S 2  of  FIG. 13A . When the third sensor  43  has not detected the bonding portion A of the two-ply sheet PJ (NO in step S 2  of  FIG. 13A ), step S 2  is repeated until the third sensor  43  detects the bonding portion A of the two-ply sheet PJ. By contrast, when the third sensor  43  has detected the bonding portion A of the two-ply sheet PJ (YES in step S 2  of  FIG. 13A ), in response to the timing of detection of the bonding portion A of the two-ply sheet PJ by the third sensor  43 , the controller  500  causes the third conveyance roller pair  6  to convey the two-ply sheet PJ in the forward direction by a predetermined amount X 1  until the gripped portion B of the two-ply sheet PJ (that is the trailing end of the two-ply sheet PJ conveyed in the forward direction, in other words, the other end of the two-ply sheet PJ) passes the position of the winding roller  20 , in step S 3  of  FIG. 13A . Note that, in a case in which the two-ply sheet PJ is the subsequent two-ply sheet PJ 2  (that is, the second or other two-ply sheet after the first two-ply sheet) in the continuous sheet laminating operation in the above-described state, the switching claw  17  (see  FIGS. 9A to 9C ) is rotated to the position to close the fourth sheet conveyance passage K 6  and open the retract sheet conveyance passage K 7 ). 
     As illustrated in  FIG. 4C , the controller  500  causes the third conveyance roller pair  6  to temporarily stop conveyance of the two-ply sheet PJ conveyed by the predetermined amount X 1  and causes the gripper  32  to move from the gripping position to the releasing position in step S 4  of  FIG. 13A . That is, the cam  34  moves to a rotational position at which the cam  34  presses the arm  31 . In this state, the gripped portion B of the two-ply sheet PJ is received between the gripper  32  and the receiving portion  20   b.    
     Then, as illustrated in  FIG. 4D , the controller  500  causes the third conveyance roller pair  6  to rotate in the reverse direction to start conveyance of the two-ply sheet PJ in the reverse direction in step S 5  of  FIG. 13A . At this time, the fourth sensor  44  detects the gripped portion B of the two-ply sheet PJ, that is, the other end of the two-ply sheet PJ and the leading end of the two-ply sheet PJ conveyed in the reverse direction. 
     Subsequently, the controller  500  determines whether the fourth sensor  44  has detected the gripped portion B of the two-ply sheet PJ, in step S 6  of  FIG. 13A . When the fourth sensor  44  has not detected the gripped portion B (NO in step S 6  of  FIG. 13A ), step S 6  is repeated until the fourth sensor  44  detects the gripped portion B of the two-ply sheet PJ. By contrast, when the fourth sensor  44  has detected the gripped portion B (YES in step S 6  of  FIG. 13A ), as illustrated in  FIG. 5A , in response to the timing of detection of the gripped portion B of the two-ply sheet PJ by the fourth sensor  44 , the controller  500  causes the third conveyance roller pair  6  to convey the two-ply sheet PJ by a predetermined amount X 2  until the gripped portion B of the two-ply sheet PJ reaches the position of the winding roller  20 , that is, the winding start position W. Then, the controller  500  causes the third conveyance roller pair  6  to stop conveyance of the two-ply sheet PJ, in step S 7  of  FIG. 13A . 
     Then, as illustrated in  FIG. 5B , the gripper  32  is moved from the releasing position to the gripping position in the state in which the gripped portion B of the two-ply sheet PJ is at the winding start position W, in step S 8  of  FIG. 13A . That is, the cam  34  moves to a rotational position at which the cam  34  does not press the arm  31 . In this state, as illustrated in  FIG. 5B ′, the end surface of the other end of the two-ply sheet PJ does not contact any member, and the gripped portion B of the two-ply sheet PJ is gripped between the gripper  32  and the receiving portion  20   b.    
     Then, as illustrated in  FIG. 5C , the winding roller  20  rotates in the reverse direction (that is, the counterclockwise direction) in a state in which the gripper  32  grips the two-ply sheet PJ, and the third conveyance roller pair  6  rotates again in the reverse direction together with the winding roller  20 . At this time, as the winding roller  20  rotates, the gap C is formed between the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ between the winding roller  20  and the third conveyance roller pair  6 , as illustrated in  FIG. 5D . At this time, as the gap C is formed, the first guide  25  and the second guide  26  limit the warp (slack) of the two-ply sheet PJ in the vicinity of the winding roller  20 . Accordingly, the gap C of the two-ply sheet PJ is intensively formed near the third conveyance roller pair  6 . 
     Since the controller  500  determines the timing at which the gripper  32  and the receiving portion  20   b  grip the gripped portion B of the two-ply sheet PJ in response to the timing of detection of the leading end of the two-ply sheet PJ conveyed in the reverse direction by the fourth sensor  44  disposed downstream from the third conveyance roller pair  6  in the reverse direction, the gripped portion B of the two-ply sheet PJ is accurately conveyed to a desired gripping position regardless of variations in the sheet lengths with respect to the sheet conveyance amount X 2 . Note that the size of sheets includes an error even if the sheets are sold as the same size. 
     Further, by detecting the leading end of the two-ply sheet PJ conveyed in the reverse direction by the fourth sensor  44 , the sheet conveyance amount X 2  that is measured according to the detection is reduced regardless of the sheet length. Therefore, the above-described configuration reduces variation in the sheet conveyance amount X 2  and accurately conveys the gripped portion B of the two-ply sheet PJ to the desired gripping position. 
     Accordingly, the fourth sensor  44  is preferably disposed near the winding roller  20 . 
     Further, a description is given of a mechanism that generates the gap C in the two-ply sheet PJ, with reference to  FIG. 5C ′. The gap C is generated in the two-ply sheet PJ between the winding roller  20  and the third conveyance roller pair  6  by winding the two-ply sheet PJ around the winding roller  20 . 
     The following description additionally indicates the mechanism. 
     The two-ply sheet PJ wound around the winding roller  20  is gripped by the gripper  32 , restricting misalignment in the sheet. Therefore, a slip is generated between the first sheet P 1  and the second sheet P 2  by the amount of the circumferential length of the winding roller  20 . As a result, the conveyance amount of the inner sheet (i.e., the first sheet P 1 ) is smaller than the conveyance amount of the outer sheet (i.e., the second sheet P 2 ). As a result, warp (slack) is generated in the inner sheet (i.e., the first sheet P 1 ) between the nip region of the third conveyance roller pair  6  and the winding roller  20 . At this time, as the two-ply sheet PJ is wound around the winding roller  20  one or more rounds, the difference in the winding circumferential length is generated between the inner circumference and the outer circumference additionally by the thickness of the sheet, which generates the warp (slack). 
     To be more specific, a distance from the rotary shaft  20   a  (i.e., the axial center) of the winding roller  20  to the second sheet P 2  on the outer side of the winding roller  20  is R+ΔR, where a distance from the rotary shaft  20   a  (i.e., the axial center) of the winding roller  20  to the first sheet P 1  on the inner side of the winding roller  20  is “R” and the thickness of the inner sheet (first sheet P 1 ) is “A R”. Since the radius of the first sheet P 1  wound around the inner side of the winding roller  20  and the radius of the second sheet P 2  wound around the outer side of the first sheet P 1  are different by the thickness A R of the first sheet P 1  (wound around the inner side of the winding roller  20 ), a circumferential length difference of 2×ΔR×π is generated between the inner sheet (first sheet P 1 ) and the outer sheet (second sheet P 2 ), when the two-ply sheet PJ is wound around the winding roller  20  by one round. Therefore, when the number of winding the two-ply sheet PJ around the winding roller  20  is M times, the slack of the inner sheet (first sheet P 1 ) is generated by the circumferential length difference of 2×ΔR×π×M. 
     Finally, the warp (slack) is accumulated between the third conveyance roller pair  6  and the winding roller  20 , and the gap C corresponding to 2×ΔR×π×M is formed between the first sheet P 1  and the second sheet P 2 . 
     Then, the controller  500  causes the third conveyance roller pair  6  and the winding roller  20  to rotate in the reverse direction. At the timing at which the third conveyance roller pair  6  has conveyed the two-ply sheet PJ by a predetermined amount X 3  since the start of winding of the two-ply sheet PJ by the winding roller  20 , the controller  500  causes the third conveyance roller pair  6  to stop conveyance of the two-ply sheet PJ and the winding roller  20  to stop winding the two-ply sheet PJ, as illustrated in  FIG. 6A , in step S 9  of  FIG. 13A . In this state, the two-ply sheet PJ is wound around the winding roller  20  one or more times, and the gap C in the two-ply sheet PJ (i.e., the distance between the first sheet P 1  and the second sheet P 2  in the vertical direction) is sufficiently widened if the two-ply sheet PJ is normally separated. 
     When the gap C is sufficiently widened, the controller  500  determines whether the sixth sensor  46  detects that the gap C equal to or larger than a predetermined distance F is formed in the two-ply sheet PJ, in step S 29  of  FIG. 13A . 
     As a result, when the controller  500  determines that the gap C is the sufficiently large gap equal to or greater than the predetermined size F, the controller  500  determines that the subsequent sheet separating operations of the separation claws  16  do not cause a problem and controls the separation claws  16  to insert into the gap C sufficiently widened in the two-ply sheet PJ, as illustrated in  FIG. 6B , in step S 10  of  FIG. 13A . That is, as illustrated in  FIGS. 11 and 12A , each of the separation claws  16  in pair is moved from the standby position to the separation position. 
     Then, as illustrated in  FIG. 6C , the third conveyance roller pair  6  and the winding roller  20  start rotating in the forward direction, that is, in the clockwise direction, in step S 11  of  FIG. 13A , in the state in which the separation claws  16  are inserted in the gap C. That is, as illustrated in  FIGS. 12A to 12C , the separation claws  16  that is inserted in the gap C of the two-ply sheet PJ relatively move from the one end (bonding portion A) to the other end (gripped portion B) with respect to the two-ply sheet PJ. Note that the above-described relative movement in the present embodiment is achieved by moving the two-ply sheet PJ itself in a direction indicated by arrow in  FIGS. 12A to 12C  without changing the positions of the separation claws  16  in the sheet conveyance direction. 
     Note that, when the controller  500  determines that the gap C in the two-ply sheet PJ is not the sufficiently large gap equal to or greater than the predetermined distance F (NO in step S 29  of  FIG. 13A ), that is, when the controller  500  determines that the abnormal state occurs based on the results detected by the sixth sensor  46 , the controller  500  determines that the subsequent sheet separating operations of the separation claws  16  cause various kinds of problems, and therefore does not move the separation claws  16  from the standby positions to the separation positions. At this time, the controller  500  causes the operation display panel  49  (see  FIG. 1 ) to notify that the occurrence of the abnormal state stops the sheet separating operation of the two-ply sheet PJ and the sheet inserting operation of the inner sheet PM, in step S 30  of  FIG. 13A . 
     Thereafter, as illustrated in  FIG. 7A , the controller  500  causes the third conveyance roller pair  6  and the winding roller  20  to stop rotating in the forward direction after the third conveyance roller pair  6  has conveyed the two-ply sheet PJ in the forward direction by a predetermined amount X 4 , in step S 12  of  FIG. 13B . At this time, the gripped portion B of the two-ply sheet PJ is positioned on the third sheet conveyance passage K 3  (that is, at the winding start position W illustrated in  FIG. 5B ), which is a state in which the gripper  32  may release the gripped portion B. In addition, as illustrated in  FIG. 12C , the separation claws  16  stop near the other end of the two-ply sheet PJ after the separation claws  16  are inserted into the gap C of the two-ply sheet PJ and relatively move to the other end (gripped portion B) of the two-ply sheet PJ with respect to the two-ply sheet PJ. 
     In this state, the gripper  32  moves from the gripping position to the releasing position in step S 13  of  FIG. 13B . That is, the cam  34  moves to a rotational position at which the cam  34  does not press the arm  31 . This state indicates that the gripper  32  releases the two-ply sheet PJ from the gripping. Note that, in the present embodiment, the cam  34  in the moving mechanism  30  moves to release the gripping of the gripper  32 . However, in a case in which the pulling force by conveyance of the two-ply sheet PJ by the third conveyance roller pair  6  is greater than the gripping force of the gripper  32  to grip the two-ply sheet PJ, the gripping of the two-ply sheet PJ by the gripper  32  is released by pulling the two-ply sheet PJ from the gripper  32  due to conveyance of the two-ply sheet PJ without moving the cam  34  in the moving mechanism  30 . 
     Thereafter, as illustrated in  FIG. 7B , the controller  500  causes the third conveyance roller pair  6  to rotate in the forward direction again to start conveyance of the two-ply sheet PJ in the forward direction, in step S 14  of  FIG. 13B . In addition, after the gripped portion B of the two-ply sheet PJ, that is, the other end of the two-ply sheet PJ and the trailing end of the two-ply sheet PJ, passes over the branch portion between the third sheet conveyance passage K 3  and each of the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5 , the gripper  32  moves from the releasing position to the gripping position. Further, at this time, the fourth sensor  44  detects the gripped portion B of the two-ply sheet PJ, that is, the other end of the two-ply sheet PJ and the trailing end of the two-ply sheet PJ conveyed in the forward direction. Then, the controller  500  determines whether the third conveyance roller pair  6  is conveyed the two-ply sheet PJ by a predetermined amount X 5  in response to the timing at which the fourth sensor  44  detects the trailing end of the two-ply sheet PJ conveyed in the forward direction, in other words, after the fourth sensor  44  has detected the gripped portion B of the two-ply sheet PJ, in step S 15  of  FIG. 13B . When the third conveyance roller pair  6  is not conveyed the two-ply sheet PJ by the predetermined amount X 5  after the fourth sensor  44  has detected the gripped portion B of the two-ply sheet PJ (NO in step S 15  of  FIG. 13B ), step S 15  is repeated until the third conveyance roller pair  6  is conveyed the two-ply sheet PJ by the predetermined amount X 5  after the fourth sensor  44  has detected the gripped portion B of the two-ply sheet PJ. By contrast, when the third conveyance roller pair  6  is conveyed the two-ply sheet PJ by the predetermined amount X 5  after the fourth sensor  44  has detected the gripped portion B of the two-ply sheet PJ (YES in step S 15  of  FIG. 13B ), as illustrated in  FIG. 12D , the controller  500  causes the third conveyance roller pair  6  to stop conveying the two-ply sheet PJ and causes the separation claws  16  to move in the width direction of the two-ply sheet PJ, in step S 28  of  FIG. 13B . As a result, as illustrated in  FIG. 7B , the trailing ends of the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ conveyed in the forward direction are separated and largely opened (see  FIG. 12D ). At this time, the controller  500  starts to perform the sheet separating operation (sheet separation) on the two-ply sheet PJ. 
     Then, as illustrated in  FIG. 7C , the third conveyance roller pair  6  rotates in the reverse direction to start conveying the two-ply sheet PJ in the reverse direction, in step S 16  of  FIG. 13B . At this time, since the separation claws  16  are disposed at the switching positions at which the separation claws  16  block the two-ply sheet PJ moving to the third sheet conveyance passage K 3  (that is, the position illustrated in  FIG. 12D ), the first sheet P 1  and the second sheet P 2  separated each other are guided to the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5 , respectively, as illustrated in  FIG. 7C . At this time, the fifth sensor  45  (see  FIG. 1 ) detects the bonding portion A of the two-ply sheet PJ, that is, the one end of the two-ply sheet PJ and the trailing end of the two-ply sheet PJ conveyed in the reverse direction. Subsequently, the controller  500  determines whether the fifth sensor  45  (see  FIG. 1 ) that functions as a sheet detector has detected the trailing end of the two-ply sheet PJ conveyed in the reverse direction, that is, the bonding portion A, in step S 17  of  FIG. 13B . In response to the timing of detection of the trailing end of the two-ply sheet PJ in the reverse direction by the fifth sensor  45  (see  FIG. 1 ), the controller  500  causes the second feed roller  3  to start feeding the inner sheet PM from the second feed tray  12 , in step S 18  of  FIG. 13B . 
     Note that the timing at which a sheet feed roller  197  starts to feed the inner sheet PM is not limited to the above-described timing. It is preferable to set the timing to reduce the time to perform the sheet separating operation and the sheet inserting operation. 
     Subsequently, as illustrated in  FIG. 8A , in response to the timing of detection of the trailing end of the two-ply sheet PJ in the reverse direction by the fifth sensor  45  (see  FIG. 1 ), the controller  500  causes the third conveyance roller pair  6  to rotate to convey the two-ply sheet PJ by a predetermined amount X 6 , and stop the conveyance of the two-ply sheet PJ when the two-ply sheet PJ has been conveyed by the predetermined amount X 6 , in step S 19  of  FIG. 13B . When the third conveyance roller pair  6  conveys the two-ply sheet PJ by the predetermined amount X 6 , the bonding portion A of the two-ply sheet PJ is in the nip region of the third conveyance roller pair  6  or at a position slightly leftward from the nip region of the third conveyance roller pair  6 . That is, the third conveyance roller pair  6  nips the one end of the two-ply sheet PJ. Then, this state is a state in which the sheet separating operation of the two-ply sheet PJ is completed. 
     Further, before completion of the sheet separating operation of the two-ply sheet PJ, the controller  500  has already started feeding the inner sheet PM from the second feed tray  12 . Therefore, as illustrated in  FIG. 8A , when the sheet separating operation on the two-ply sheet PJ is completed, the leading end of the inner sheet PM (i.e., at one end of the inner sheet PM in the forward direction) has approached the position at which the inner sheet PM is inserted between the first sheet P 1  and the second sheet P 2  constructing the two-ply sheet PJ. 
     On the other hand, the third sensor  43  detects the leading end of the inner sheet PM (i.e., at one end of the inner sheet PM in the forward direction). In addition, as illustrated in  FIG. 8B , in response to the detection timing, the separation claws  16  move to the respective standby positions at the timing at which the separation claws  16  do not block conveyance of the inner sheet PM. 
     Further, as illustrated in  FIGS. 8C and 12E , the controller  500  determines whether the third sensor  43  has detected the leading end of the inner sheet PM in the forward direction, in step S 20  of  FIG. 13B . When the third sensor  43  has not detected the leading end of the inner sheet PM in the forward direction (NO in step S 20  of  FIG. 13B ), step S 20  is repeated until the third sensor  43  has not detected the leading end of the inner sheet PM in the forward direction. By contrast, when the third sensor  43  has detected the leading end of the inner sheet PM in the forward direction (YES in step S 20  of  FIG. 13B ), in response to the detection timing, the controller  500  causes the second conveyance roller pair  5  to convey the inner sheet PM by a predetermined amount X 7 . Then, the controller  500  causes the third conveyance roller pair  6  to start conveying the two-ply sheet PJ in the forward direction again, in step S 21  of  FIG. 13B . At this time, the inner sheet PM is accurately nipped at a desired position between the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ. 
     Thus, the controller  500  finishes the sheet inserting operation to insert the inner sheet PM in the two-ply sheet PJ, in other words, between the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ (step S 22  of  FIG. 14 ). 
     At this time, as illustrated in  FIG. 9A , the switching claw  17  (see  FIG. 1 ) opens the fourth sheet conveyance passage K 6  (in step S 23  of  FIG. 14 ). Thereafter, the controller  500  causes the third conveyance roller pair  6  to convey the two-ply sheet PJ (in which the inner sheet PM has been inserted after the sheet separating operation) to pass through the fourth sheet conveyance passage K 6 , and is then conveyed to the sheet lamination device  51 . 
     Then, as illustrated in  FIG. 9B , the sheet lamination device  51  starts to perform the sheet laminating operation on the two-ply sheet PJ (i.e., the preceding two-ply sheet PJ 1 ) (in step S 31  of  FIG. 14 ). That is, while the two-ply sheet PJ (i.e., the preceding two-ply sheet PJ 1 ) is conveyed in the sheet lamination device  51 , the entire area of the two-ply sheet PJ is gradually bonded with the inner sheet PM being inserted in the two-ply sheet PJ. At this time, the subsequent two-ply sheet PJ 2  (before separation) is conveyed from the first feed tray  11  to the sheet separation device  1  without interfering the preceding two-ply sheet PJ 1 . 
     Then, as illustrated in  FIG. 9C , after the fifth sensor  45  detects the trailing end of the preceding two-ply sheet PJ 1  (that is the trailing end of the preceding two-ply sheet PJ 1  conveyed in the forward direction, in other words, the other end of the preceding two-ply sheet PJ 1 ), the controller  500  determines whether the preceding two-ply sheet PJ 1  is conveyed by a predetermined amount X 8  (in step S 32  of  FIG. 14 ). When the preceding two-ply sheet PJ 1  is not conveyed by the predetermined amount X 8  (NO in step S 32  of  FIG. 14 ), step S 32  is repeated until the preceding two-ply sheet PJ 1  is conveyed by the predetermined amount X 8 . By contrast, when the preceding two-ply sheet PJ 1  is conveyed by the predetermined amount X 8  (YES in step S 32  of  FIG. 14 ), in response to this timing of detection of conveyance of the preceding two-ply sheet PJ 1 , the sheet separating operation is started on the two-ply sheet PJ 2  (step S 33  of  FIG. 14 ). This timing indicates a timing at which the trailing end of the preceding two-ply sheet PJ 1  passes the branching point of the fourth sheet conveyance passage K 6  and the retract sheet conveyance passage K 7 . At this time, as illustrated in  FIG. 9C , the switching claw  17  closes the fourth sheet conveyance passage K 6  and the opens the retract sheet conveyance passage K 7 . Then, the third conveyance roller pair  6  and the second ejection roller pair  8 , each rotating in arrow in  FIG. 9C , guide the subsequent two-ply sheet PJ 2  into the retract sheet conveyance passage K 7  to convey the subsequent two-ply sheet PJ 2  to the second ejection tray  55  (retract portion). At this time, the trailing end of the subsequent two-ply sheet PJ 2  (gripped portion B) may not be located upstream from the winding start position W of the winding roller  20  (see  FIG. 5B ). A part of the subsequent two-ply sheet PJ 2 , which is protruded upstream from the third conveyance roller pair  6  in the sheet conveyance direction, is temporarily purged into the retract sheet conveyance passage K 7 . 
     Then, as illustrated in  FIG. 9C , the controller  500  causes each of the winding roller  20 , the third conveyance roller pair  6 , and the second ejection roller pair  8  to rotate in the direction indicated by arrow in  FIG. 9C , so that the subsequent two-ply sheet PJ 2  is wound around the winding roller  20 . 
     Further, as illustrated in  FIG. 10A , the controller  500  starts to peel (separate) the first sheet P 1  and the second sheet P 2  constructing the subsequent two-ply sheet PJ 2  and to feed the inner sheet PM from the second feed tray  12 . The inner sheet PM is to be inserted into the subsequent two-ply sheet PJ 2 . The series of the sheet separating operation and the sheet inserting operation performed on the subsequent two-ply sheet PJ 2  is same as the series of the sheet separating operation and the sheet inserting operation performed on the preceding two-ply sheet PJ 1 , which was described with reference to  FIGS. 4A to 8C . 
     Then, as illustrated in  FIG. 10B , the controller  500  determines whether the preceding two-ply sheet PJ 1  passed through the nip region (the extreme upstream portion) of the first heat-pressure roller pair  51   a  (in step S 34  of  FIG. 14 ). When the preceding two-ply sheet PJ 1  has not passed through the nip region (the extreme upstream portion) of the first heat-pressure roller pair  51   a  (NO in step S 34 ), step S 34  is repeated until the preceding two-ply sheet PJ 1  passes through the nip region of the first heat-pressure roller pair M a. On the other hand, when the preceding two-ply sheet PJ 1  passed through the nip region of the first heat-pressure roller pair  51   a  (YES in step S 34 ), in response to the timing at which the trailing end of the preceding two-ply sheet PJ 1  passes through the nip region of the first heat-pressure roller pair  51   a , the subsequent two-ply sheet PJ 2  in which the inner sheet PM being inserted is conveyed toward the sheet lamination device  51  (in step S 35  of  FIG. 14 ). At this time, the switching claw  17  is rotated to the position to open the fourth sheet conveyance passage K 6  and close the retract sheet conveyance passage K 7 . Note that, in the present embodiment, the timing at which the trailing end of the preceding two-ply sheet PJ 1  passes through the nip region of the first heat-pressure roller pair  51   a  is determined based on the timing at which the fifth sensor  45  detected the trailing end of the preceding two-ply sheet PJ 1 . However, the timing at which the trailing end of the preceding two-ply sheet PJ 1  passes through the nip region of the first heat-pressure roller pair  51   a  may be determined based on the rotation time of the first heat-pressure roller pair  51   a . Alternatively, a sheet detection sensor may be disposed proximate to the first heat-pressure roller pair  51   a  to directly detect the trailing end of the preceding two-ply sheet PJ 1 . 
     Then, as illustrated in  FIG. 10C , the controller  500  causes the sheet lamination device  51  to start to perform the sheet laminating operation on the subsequent two-ply sheet PJ 2  (step S 36  in  FIG. 14 ). Further, after the sheet laminating operation is performed on the preceding two-ply sheet PJ 1 , the preceding two-ply sheet PJ 1  is ejected to the outside of the image forming apparatus  100  by the first ejection roller pair  7  and is stacked on the first ejection tray  13 . 
     Thereafter, the controller  500  determines whether or not there is no two-ply sheet following the subsequent two-ply sheet PJ 2  (another subsequent two-ply sheet) (in step S 37  of  FIG. 14 ). When there is another two-ply sheet following the subsequent two-ply sheet PJ 2  (NO in step S 37 ), step goes back to step S 32  and steps S 32  to S 37  are repeated until no more two-ply sheet is detected. 
     By contrast, when there is no two-ply sheet following the subsequent two-ply sheet PJ 2  (YES in step S 37 ), the controller  500  determines whether the sheet laminating operation on the subsequent two-ply sheet PJ 2  is finished (in step S 38  of  FIG. 14 ). When the sheet laminating operation on the subsequent two-ply sheet PJ 2  is not finished (NO in step S 38 ), step S 38  is repeated until it is determined that the sheet laminating operation on the subsequent two-ply sheet PJ 2  is finished. On the other hand, when the sheet laminating operation on the subsequent two-ply sheet PJ 2  is finished (YES in step S 38 ), the subsequent two-ply sheet PJ 2  is ejected and stacked on the first ejection tray  13 , and the flow in  FIG. 14  ends. 
     As described above, the sheet laminator  50  according to the present embodiment performs the sheet laminating operation as a sequence of the following operations: an operation to feed the two-ply sheet PJ; an operation to separate the first sheet P 1  and the second sheet P 2  of the two-ply sheet PJ; an operation to insert the inner sheet PM into the space between the first sheet P 1  and the second sheet P 2 ; and an operation to perform the sheet laminating operation on the two-ply sheet PJ in which the inner sheet PM is inserted. By so doing, the user convenience for the sheet laminator  50  is enhanced. Further, in a case in which the sheet laminator  50  performs the sheet laminating operation on a plurality of two-ply sheets PJ including the preceding two-ply sheet PJ 1  and the subsequent two-ply sheet PJ 2 , when the sheet laminating operation is performed on the preceding two-ply sheet PJ 1 , the sheet separating operation is performed on the subsequent two-ply sheet PJ 2 . Accordingly, the productivity of the sheet laminator  50  and the image forming apparatus  100  is enhanced. 
     Variation 1 
     A description is given of the continuous sheet laminating operation of the sheet laminator  50  according to Variation 1. 
       FIGS. 16A and 16B  are schematic views, each illustrating a part of operations in the continuous sheet laminating operation of the sheet laminator  50 , according to Variation 1. 
       FIGS. 16A and 16B  correspond to  FIGS. 10B and 10C  according to the present embodiment. 
     As illustrated in  FIGS. 16A and 16B , the configuration and functions of the sheet laminator  50  according to Variation 1 are basically identical to the configuration and functions of the sheet laminator  50  according to the present embodiment. That is, the sheet laminator  50  of Variation 1 includes a sheet lamination device  51 A including a single heat-pressure roller pair, i.e., a heat-pressure roller pair  51   a A, while the sheet laminator  50  according to the present embodiment includes the sheet lamination device  51  including three heat-pressure roller pairs (i.e., the first heat-pressure roller pair  51   a , the second heat-pressure roller pair  51   b , and the third heat-pressure roller pair  51   c ). 
     Similar to the continuous sheet laminating operation performed by the sheet laminator  50  according to the present embodiment, as illustrated in  FIGS. 16A and 16B , the continuous sheet laminating operation performed by the sheet laminator  50  of Variation 1 having the above-described configuration is controlled so that the trailing end of the preceding two-ply sheet PJ 1  passes the extreme upstream portion (i.e., the nip region of the heat-pressure roller pair  51   a A) of the sheet lamination device  51 A, and then the leading end of the subsequent two-ply sheet PJ 2  is fed and inserted into the extreme upstream portion (i.e., the nip region of the heat-pressure roller pair  51   a A). 
     Therefore, the continuous sheet laminating operation is performed in a state in which the gap (space) between the preceding two-ply sheet PJ 1  and the subsequent two-ply sheet PJ 2  is further reduced (narrowed). Accordingly, the time to finish the entire sheet laminating operation (series of jobs) on the plurality of two-ply sheets PJ is reduced, thereby enhancing the productivity of the sheet laminator  50 . 
     Variation 2 
     A description is given of an image forming apparatus according to Variation 2, with reference to  FIG. 17 . 
       FIG. 17  is a schematic view illustrating an image forming apparatus, according to Variation 2. 
     As illustrated in  FIG. 17 , an image forming apparatus  100  according to Variation 2 that forms an image on a sheet P includes the sheet laminator  50  illustrated in  FIG. 1 , on a housing  100   a  of the image forming apparatus  100 . The housing  100   a  holds an image forming device  101  that performs an image forming operation in the image forming apparatus  100  to form an image on a sheet such as the inner sheet PM. However, in the image forming apparatus  100 , the sheet P that is fed from a sheet feeding device  112  and conveyed by the sheet feed roller  197  is conveyed as the inner sheet PM to the sheet laminator  50 . 
     With reference to  FIG. 17 , in the image forming apparatus  100 , multiple pairs of sheet conveying rollers disposed in a document feeder  110  feed an original document D from a document loading table and convey the original document D in a direction indicated by arrow in  FIG. 17 . By so doing, the original document D passes over a document reading device  102 . At this time, the document reading device  102  optically reads image data of the original document D passing over the document reading device  102 . 
     The image data optically read by the document reading device  102  is converted into electrical signals and transmitted to a writing device  103 . The writing device  103  emits laser beams onto photoconductor drums  105 Y,  105 M,  105 C, and  105 K, based on the electrical signals of the image data in each of colors, respectively. By so doing, an exposure process is executed by the writing device  103 . 
     On the photoconductor drums  105 Y,  105 M,  105 C, and  105 K of respective image forming units  104 Y,  104 M,  104 C, and  104 K, a charging process, the exposure process, and a developing process are executed to form desired images on the photoconductor drums  105 Y,  105 M,  105 C, and  105 K, respectively. 
     The images formed on the photoconductor drums  105 Y,  105 M,  105 C, and  105 K are transferred and superimposed onto an intermediate transfer belt  178  to form a color image. The color image formed on the intermediate transfer belt  178  is transferred onto the surface of a sheet P (which is a sheet to function as the inner sheet PM) fed and conveyed by the sheet feed roller  197  from the sheet feeding device  112  that functions as a second sheet feeder, at a position at which the intermediate transfer belt  178  faces a secondary transfer roller  189 . 
     After the color image is transferred onto the surface of the sheet P (that is, the inner sheet PM), the sheet P is conveyed to the position of a fixing device  120 . The fixing device  120  fixes the transferred color image on the surface of the sheet P, to the sheet P. 
     Thereafter, the sheet P is ejected from the image forming device  130  of the image forming apparatus  100  by an ejection roller pair  131 , and is fed as the inner sheet PM, into the sheet laminator  50 . At this time, when the sheet laminator  50  receives the inner sheet PM, the sheet laminator  50  has completed the operation described with reference to  FIGS. 4A to 7C  (that is, the operation to separate the two-ply sheet PJ) and performs the operation described with reference to  FIGS. 8A to 8C  (that is, the operation to insert the inner sheet PM into the two-ply sheet PJ) after the sheet laminator  50  receives the inner sheet PM. Further, after the sheet lamination device  51  has completed the sheet laminating operation on the two-ply sheet PJ in which the inner sheet PM is inserted, the second ejection roller pair  8  ejects the two-ply sheet PJ to the outside of the sheet lamination device  51  to stack the two-ply sheet PJ on the first ejection tray  13 . 
     As described above, a series of image forming operations (i.e., the printing operations) in the image forming apparatus  100  and a series of sheet separating operation of the two-ply sheet PJ and the sheet laminating operation of the inner sheet PM on which the image is formed are completed. 
     Then, even in the image forming apparatus  100  having the above-described configuration, when the continuous sheet laminating operation is performed, the sheet separating operation is started to be performed on the subsequent two-ply sheet PJ 2  while the sheet laminating operation is being performed on the preceding two-ply sheet PJ 1 . Accordingly, the overall productivity of the image forming apparatus  100  is enhanced. 
     Note that the image forming apparatus  100  further includes the operation display panel  49 . When the controller  500  determines that the abnormal state occurs based on the results detected by the sixth sensor  46  that functions as an abnormality detection sensor, the controller  500  causes the operation display panel  49  to display that the occurrence of the abnormal state stops the sheet separating operation of the two-ply sheet PJ and the sheet inserting operation of the inner sheet PM. 
     Further, the image forming apparatus  100  according to Variation 2 of the present disclosure is a color image forming apparatus but may be a monochrome image forming apparatus. Further, the image forming apparatus  100  according to Variation 2 of the present disclosure employs electrophotography, but the present disclosure is not limited to an electrophotographic image forming apparatus. For example, the present disclosure may be applied to other types of image forming apparatuses such as an inkjet image forming apparatus and a stencil printing machine. 
     Variation 3 
     A description is given of an image forming system according to Variation 3, with reference to  FIG. 18 . 
     As illustrated in  FIG. 18 , an image forming system  200  according to Variation 3 includes the image forming apparatus  100  the sheet laminator  50 . 
     In the image forming system  200 , the image forming apparatus  100  includes the image forming device  101  disposed in the housing  100   a , and the sheet laminator  50  includes the sheet separation device  1  and the sheet lamination device  51 . The sheet laminator  50  is detachably attached to the housing  100   a  of the image forming apparatus  100 . As in the image forming apparatus  100  of Variation 2, the sheet P that is fed from the sheet feeding device  112  and conveyed by the sheet feed roller  197  is conveyed as the inner sheet PM to the sheet laminator  50  in the image forming apparatus  100  of Variation 3. 
     In the image forming system  200  illustrated in  FIG. 18 , the image forming apparatus  100  performs the image forming operations on the sheet P, as described above with reference to  FIG. 17 . Then, the image forming apparatus  100  ejects the sheet P (that is, the inner sheet PM on which a desired image is formed) from the ejection roller pair  131  to the sheet laminator  50 . Then, after the sheet P is conveyed to the sheet laminator  50 , the sheet P is inserted into the two-ply sheet PJ, where the sheet laminator  50  performs the sheet laminating operation on the two-ply sheet PJ. Then, the first ejection roller pair  7  ejects the two-ply sheet PJ to the outside of the sheet laminator  50  to stack the two-ply sheet PJ on the first ejection tray  13 . 
     Then, even in the image forming apparatus  100  having the above-described configuration, when the continuous sheet laminating operation is performed, the sheet separating operation is started to be performed on the subsequent two-ply sheet PJ 2  while the sheet laminating operation is being performed on the preceding two-ply sheet PJ 1 . Accordingly, the overall productivity of the image forming apparatus  100  is enhanced. 
     When the above-described sheet laminating operation is not performed, the image forming apparatus  100  of the image forming system  200  according to Variation 3 ejects the sheet P having the image formed in the image forming operations, from a second ejection roller pair  132  to the outside of the image forming apparatus  100 , so as to stack the sheet P on a second ejection tray  150 . 
     As described above, the sheet laminator  50  is detachably attached to the housing  100   a  of the image forming apparatus  100 . When the sheet laminator  50  is not used, the sheet laminator  50  may be detached from the image forming apparatus  100 . In a case in which the sheet laminator  50  is removed from the image forming apparatus  100 , a placement surface  149  on which the sheet laminator  50  was installed functions as an ejection tray, and the sheet P that is ejected from the ejection roller pair  131  to the outside of the image forming apparatus  100  is stacked on the placement surface  149 , in other words, the sheet P on which a desired image is formed is stacked on the placement surface  149 . 
     As described above, the sheet laminator  50  according to the present embodiment includes the sheet separation device  1  that performs the sheet separating operation and the sheet inserting operation. To be more specific, the sheet separation device  1  performs the sheet separating operation to separate the non-bonding portion of the two-ply sheet PJ in which two sheets, which are the first sheet P 1  and the second sheet P 2 , are overlapped and bonded together at one end of the two-ply sheet PJ as the bonding portion A of the two-ply sheet PJ. The sheet separation device  1  then performs the sheet inserting operation to insert the inner sheet PM between the first sheet P 1  and the second sheet P 2  separated from each other by the sheet separating operation. The sheet laminator  50  according to the present embodiment further includes the sheet lamination device  51  that performs the sheet laminating operation on the two-ply sheet PJ after the sheet separating operation and the sheet inserting operation are performed on the two-ply sheet PJ by the sheet separation device  1 . Then, in a case in which the sheet laminator  50  performs the sheet laminating operation on the plurality of two-ply sheets PJ including the preceding two-ply sheet PJ 1  and the subsequent two-ply sheet PJ 2 , when the sheet lamination device  51  is performing the sheet laminating operation on the preceding two-ply sheet PJ 1 , the sheet separation device  1  that performs the sheet separating operation and the sheet inserting operation performs at least the sheet separating operation on the subsequent two-ply sheet PJ 2 . 
     Accordingly, the sheet laminator  50  of the image forming apparatus  100  achieves the enhanced productivity in the sheet laminating operation on the plurality of two-ply sheets, e.g., the first sheet P 1  and the second sheet P 2 . 
     Note that, in the present embodiment, the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  branch off in different directions from the third sheet conveyance passage K 3  (sheet conveyance passage) between the separation claws  16  each functioning as a separator and the winding roller  20 . By contrast, the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  may branch off at the position of the separation claws  16  (each functioning as a separator) in different directions from the third sheet conveyance passage K 3  (sheet conveyance passage), resulting that the third sheet conveyance passage K 3  is interposed between the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5 . 
     Further, in the present embodiment, the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  are formed in a substantially U shape extending from the branch portion to the right side of  FIG. 2 . However, the shape of the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  is not limited to the above-described U shape. For example, the first branched sheet conveyance passage K 4  and the second branched sheet conveyance passage K 5  may be formed in a substantially U shape extending from the branch portion to the left in  FIG. 2  or may be formed in a substantially S shape extending from the branch portion to both the left and right in  FIG. 2 . 
     Further, even when the above-described sheet separation devices are applied, these sheet separation devices achieve the same effect as the effect provided by the configuration(s) in the present embodiment. 
     Note that embodiments of the present disclosure are not limited to the above-described embodiments and it is apparent that the above-described embodiments can be appropriately modified within the scope of the technical idea of the present disclosure in addition to what is suggested in the above-described embodiments. 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. 
     Note that, in the present disclosure, the “end surface” of the two-ply sheet is defined as a side surface extending in the thickness direction and connecting the front surface and the back surface of the two-ply sheet. Accordingly, there are four end surfaces of the rectangular two-ply sheet on the front, back, left, and right. 
     The present disclosure is not limited to specific embodiments described above, and numerous additional modifications and variations are possible in light of the teachings within the technical scope of the appended claims. It is therefore to be understood that, the disclosure of this patent specification may be practiced otherwise by those skilled in the art than as specifically described herein, and such, modifications, alternatives are within the technical scope of the appended claims. Such embodiments and variations thereof are included in the scope and gist of the embodiments of the present disclosure and are included in the embodiments described in claims and the equivalent scope thereof. 
     The effects described in the embodiments of this disclosure are listed as the examples of preferable effects derived from this disclosure, and therefore are not intended to limit to the embodiments of this disclosure. 
     The embodiments described above are presented as an example to implement this disclosure. The embodiments described above are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, or changes can be made without departing from the gist of the invention. These embodiments and their variations are included in the scope and gist of this disclosure and are included in the scope of the invention recited in the claims and its equivalent. 
     Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.