Patent Publication Number: US-2021188580-A1

Title: Sheet space-detecting device, sheet space-detecting method, and sheet-welding method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage entry according to 35 U.S.C. 371 of PCT Application No. PCT/JP2018/044704, filed on Dec. 5, 2018, which claims priority to Japanese Application No. 2017-233606, filed on Dec. 5, 2017, which is entirely incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a sheet space-detecting device, a sheet space-detecting method and a sheet-welding method. 
     BACKGROUND 
     A fiber reinforced plastic sheet (FRP sheet), which uses carbon fiber or glass fiber as reinforcing fiber, is lightweight and has high durability, and thus is used for various structural members configuring automobiles, aircrafts and the like. Such an FRP sheet has very high tensile strength and toughness in the fiber direction thereof, but has low tensile strength and toughness in a direction orthogonal to the fiber direction. In order to reduce the anisotropy of the FRP sheet, method and apparatus for laminating a plurality of FRP sheets in a state of varying the fiber directions thereof from each other are conventionally known (for example, refer to Patent Document 1). 
     DOCUMENT OF RELATED ART 
     Patent Document 
     [Patent Document 1] PCT International Publication No. WO 2015/152325 A1 
     SUMMARY 
     Technical Problem 
     In the above conventional technology, in order to laminate FRP sheets having different fiber directions, FRP sheets having various fiber directions are cut from an FRP raw sheet having a fiber angle of 0°, and the cut FRP sheets are joined together by welding in the front-rear direction. At this time, in order that the rear end of an FRP sheet on the front side does not overlap the front end of an FRP sheet on the rear side, an optical space-detecting sensor is arranged to manage the size of space between the rear end and the front end of the FRP sheets. However, the front end and the rear end of the FRP sheets may hang down or fibers of which may fluff, which may cause variations in the detection accuracy of the space. 
     The present disclosure is made in view of the above problems, and an object thereof is to improve the detection accuracy of the space between the front end and the rear end of the FRP sheets. 
     Solution to Problem 
     In order to solve the above problems, a sheet space-detecting device of a first aspect of the present disclosure is a sheet space-detecting device that detects a space between a rear end of a preceding first fiber reinforced plastic sheet and a front end of a following second fiber reinforced plastic sheet in a conveyance path for fiber reinforced plastic sheets and includes: a light-detecting sensor that projects detection light on an area including the rear end of the first fiber reinforced plastic sheet, the front end of the second fiber reinforced plastic sheet, and a reference surface exposed from the space and receives reflected light thereof; and a spacer that supports the rear end of the first fiber reinforced plastic sheet and the front end of the second fiber reinforced plastic sheet in a state where the rear end and the front end are separated from the reference surface, in an area including at least a light-projected area on which the detection light is projected. 
     In the sheet space-detecting device of the first aspect of the present disclosure, the spacer may include a first support area that supports the first fiber reinforced plastic sheet, a second support area that supports the second fiber reinforced plastic sheet, and a step area provided between the first support area and the second support area. 
     In the sheet space-detecting device of the first aspect of the present disclosure, the step area may not extend to an edge of the spacer. 
     In the sheet space-detecting device of the first aspect of the present disclosure, the step area may be a groove having a bottom portion, and a direct reflection-limiting member forming the reference surface may be disposed on the bottom portion. 
     The sheet space-detecting device of the first aspect of the present disclosure may include a moving device that retracts the spacer from the light-projected area, and a rear end portion of the spacer may be formed to more swell up than a front end portion of the spacer. 
     A sheet space-detecting method of a second aspect of the present disclosure is a sheet space-detecting method of detecting a space between a rear end of a preceding first fiber reinforced plastic sheet and a front end of a following second fiber reinforced plastic sheet in a conveyance path for fiber reinforced plastic sheets, which includes: a spacer-disposing step of disposing a spacer such that the rear end of the first fiber reinforced plastic sheet and the front end of the second fiber reinforced plastic sheet are separated from a reference surface; and a light-detecting step of, after the spacer-disposing step, projecting detection light on an area including the rear end of the first fiber reinforced plastic sheet, the front end of the second fiber reinforced plastic sheet, and the reference surface exposed from the space and receiving reflected light thereof. 
     In the sheet space-detecting method of the second aspect of the present disclosure, an orientation direction of reinforcing fiber of the first fiber reinforced plastic sheet and the second fiber reinforced plastic sheet may be parallel to the space. 
     In the sheet space-detecting method of the second aspect of the present disclosure, the spacer may include a first support area that supports the first fiber reinforced plastic sheet, a second support area that supports the second fiber reinforced plastic sheet, and a step area provided between the first support area and the second support area, and the spacer-disposing step may include a first step of supporting the first fiber reinforced plastic sheet by the first support area, and disposing the rear end of the first fiber reinforced plastic sheet above the step area, and a second step of supporting the second fiber reinforced plastic sheet by the second support area, and disposing the front end of the second fiber reinforced plastic sheet above the step area such that the front end is separated from the rear end of the first fiber reinforced plastic sheet. 
     A sheet-welding method of a third aspect of the present disclosure is a sheet-welding method of detecting, based on the sheet space-detecting method of the second aspect, the space, and welding the rear end of the first fiber reinforced plastic sheet and the front end of the second fiber reinforced plastic sheet, which includes: a sheet position-correcting step of, after the light-detecting step, correcting a position of the second fiber reinforced plastic sheet with respect to the first fiber reinforced plastic sheet; a sheet-positioning step of, after the sheet position-correcting step, holding down a rear end portion other than the rear end of the first fiber reinforced plastic sheet, and holding down a front end portion other than the front end of the second fiber reinforced plastic sheet; and a sheet-welding step of, after the sheet-positioning step, welding the rear end of the first fiber reinforced plastic sheet and the front end of the second fiber reinforced plastic sheet. 
     Effects 
     According to the present disclosure, the detection accuracy of the space between the front end and the rear end of FRP sheets. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view schematically showing an FRP sheet-laminating device of the present disclosure. 
         FIG. 2  is a side view schematically showing the FRP sheet-laminating device of the present disclosure. 
         FIG. 3  is an exploded perspective view schematically showing an FRP sheet laminate formed by the FRP sheet-laminating device of the present disclosure. 
         FIG. 4  is a perspective view schematically showing a cutting device of the present disclosure. 
         FIG. 5  is a plan view schematically showing the arrangement of FRP sheets of the present disclosure. 
         FIG. 6  is a front view of a sheet space-detecting device and a welding device of the present disclosure viewed in a sheet flow direction. 
         FIG. 7  is a plan view schematically showing the position of a light-detecting sensor and the shape of a spacer of the present disclosure. 
         FIG. 8  is a front view of the sheet space-detecting device viewed in the sheet flow direction when the welding device of the present disclosure performs welding. 
         FIG. 9A  is a side view schematically showing the operation of the sheet space-detecting device and the operation of the welding device of the present disclosure. 
         FIG. 9B  is a side view schematically showing the operation of the sheet space-detecting device and the operation of the welding device of the present disclosure. 
         FIG. 9C  is is a side view schematically showing the operation of the sheet space-detecting device and the operation of the welding device of the present disclosure. 
         FIG. 10A  is a side view schematically showing the operation of the sheet space-detecting device and the operation of the welding device of the present disclosure. 
         FIG. 10B  is a side view schematically showing the operation of the sheet space-detecting device and the operation of the welding device of the present disclosure. 
         FIG. 11A  is a side view schematically showing the operation of the sheet space-detecting device and the operation of the welding device of the present disclosure. 
         FIG. 11B  is a side view schematically showing the operation of the sheet space-detecting device and the operation of the welding device of the present disclosure. 
         FIG. 12  is a side cross-sectional view schematically showing a spacer of a modification of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a sheet space-detecting device, a sheet space-detecting method and a sheet-welding method will be described with reference to the drawings. In the following description, a “fiber reinforced plastic sheet” is simply referred to as an “FRP sheet”. 
       FIG. 1  is a plan view schematically showing an FRP sheet-laminating device  1  of the present disclosure.  FIG. 2  is a side view schematically showing the FRP sheet-laminating device  1  of the present disclosure. 
     The FRP sheet-laminating device  1  is a conveyance system that laminates a plurality of FRP sheets while conveying the FRP sheets. The FRP sheet-laminating device  1  includes an unrolling device  2  that unrolls an FRP raw sheet P 1  from a state wound in a roll, a main conveyance path  3  that causes the FRP raw sheet P 1  unrolled from the unrolling device  2  to travels, and a transfer device  4  that draws an FRP sheet laminate P 5  having traveled on the main conveyance path  3  and sends it further downstream. 
     Note that a downstream side of the main conveyance path  3  in the conveyance direction of the FRP raw sheet P 1  may be referred to as a front side and an upstream side thereof may be referred to as a rear side. 
       FIG. 3  is an exploded perspective view schematically showing the FRP sheet laminate P 5  formed by the FRP sheet-laminating device  1  of the present disclosure. 
     As shown in  FIG. 3 , the FRP sheet laminate P 5  has a structure in which an FRP sheet P 2 , an FRP raw sheet P 3  and an FRP sheet P 4  are sequentially laminated on the FRP raw sheet P 1 . 
     Note that in a direction perpendicular to the plate surface of the FRP raw sheet P 1  or the FRP sheet laminate P 5 , a side on which the FRP sheet P 4  is provided may be referred to as an upper side, and a side on which the FRP raw sheet P 1  is provided may be referred to as a lower side. 
     The FRP raw sheet P 1  is formed of reinforcing fibers such as carbon fibers or glass fibers impregnated with, for example, a thermoplastic resin to have a thickness of about 50 to 300 μm. In the FRP raw sheet P 1 , the reinforcing fibers F (the longitudinal directions of the reinforcing fibers F) are made to be in a direction. The FRP raw sheet P 1  is formed such that the orientation directions of the reinforcing fibers F (the length directions of the reinforcing fibers F) substantially match the length direction of the FRP raw sheet P 1 . The orientation direction of the reinforcing fiber F is referred to as 0°. 
     As shown in  FIG. 1 , the FRP sheet-laminating device  1  includes a first FRP sheet-forming section  5  that forms the FRP sheet P 2 , and a second FRP sheet-forming section  14  that forms the FRP sheet P 4 . In addition, the FRP sheet-laminating device  1  includes a welding device  11  that welds the FRP sheets P 2  together arranged in front and rear, and a welding device  20  that welds the FRP sheets P 4  together arranged in front and rear. The welding devices  11  and  20  are provided with sheet space-detecting devices  10  and  19  to be described later. 
     As shown in  FIG. 2 , the unrolling device  2  includes a roller and is configured to unroll the FRP raw sheet P 1  in the length direction thereof from a state wound in a roll and to send it onto the main conveyance path  3 . As shown in  FIG. 1 , the main conveyance path  3  is a support table provided in a linear shape (straight plate shape) having a width greater than that of the FRP raw sheet P 1 . The upper surface (supporting surface) of the main conveyance path  3  is formed into a smooth surface with a low frictional resistance such that the FRP raw sheet P 1  can smoothly travel. 
     The transfer device  4  includes a pair of rollers  4   a  arranged in upper and lower as shown in  FIG. 2 , and a drive source  4   b  such as a motor connected to either one of the pair of rollers  4   a  as shown in  FIG. 1 . The transfer device  4  holds the FRP sheet laminate P 5  having traveled on the main conveyance path  3  between the pair of rollers  4   a,  and draws the FRP sheet laminate P 5  through rotation of the roller  4   a  by the drive source  4   b  to send it downstream. 
     As shown in  FIG. 1 , the first FRP sheet-forming section  5  is provided in a further upstream area than the main conveyance path  3 . The first FRP sheet-forming section  5  includes a feeding device  6  that sends out an FRP raw sheet P 1  from a state wound in a roll, a sub-conveyance path  7  that causes the FRP raw sheet P 1  sent out from the feeding device  6  to travel, and a cutting device  8  that cuts the FRP raw sheet P 1  having traveled on the sub-conveyance path  7  in a width direction thereof at a predetermined angle. In the FRP raw sheet P 1  sent out from the feeding device  6 , the orientation direction of the reinforcing fiber F thereof is 0° similar to the FRP raw sheet P 1  unrolled by the unrolling device  2  onto the main conveyance path  3 . 
     The feeding device  6  includes an unrolling device  6   a  that unrolls the FRP raw sheet P 1  from a state wound in a roll, and a transfer device  6   b  that transfers the FRP raw sheet P 1  unrolled by the unrolling device  6   a  onto the sub-conveyance path  7 . The unrolling device  6   a  has a configuration similar to the unrolling device  2  described above and is configured to unroll the FRP raw sheet P 1  in the length direction thereof from a state wound in a roll and to send it onto the sub-conveyance path  7 . 
     The transfer device  6   b  is configured to be similar to the transfer device  4  described above and includes a pair of rollers  6   c  arranged in upper and lower and a drive source  6   d  such as a motor connected to either one of the pair of rollers  6   c.  The transfer device  6   b  holds the FRP raw sheet P 1  unrolled by the unrolling device  6   a  between the pair of rollers  6   c,  and draws the FRP raw sheet P 1  through rotation of the roller  6   c  by the drive source  6   d  to send it downstream of the sub-conveyance path  7 . 
     The sub-conveyance path  7  is arranged on one side of the main conveyance path  3 . The sub-conveyance path  7  extends so as to be orthogonal to the main conveyance path  3 . The sub-conveyance path  7  is also a support table provided in a linear shape (straight plate shape) having a width greater than that of the FRP raw sheet P 1  similar to the main conveyance path  3 . The upper surface (supporting surface) of the sub-conveyance path  7  is formed into a smooth surface with a low frictional resistance such that the FRP raw sheet P 1  can smoothly travel. 
       FIG. 4  is a perspective view schematically showing the cutting device  8  of the present disclosure. 
     As shown in  FIG. 4 , the cutting device  8  cuts the FRP raw sheet P 1  having traveled on the sub-conveyance path  7  in a width direction thereof at a predetermined angle. The cutting device  8  includes a cutter  8   a,  a holding bar  8   b  that movably holds the cutter  8   a,  and a pair of support parts  8   c  that support both end portions of the holding bar  8   b.    
     The cutter  8   a  is configured to reciprocate in the length direction of the holding bar  8   b  by a driving device such as a motor. The cutter  8   a  cuts the FRP raw sheet P 1  by moving on the outward path and returns to the initial position by moving on the return path to stand by for a new cutting. 
     The holding bar  8   b  has, for example, an elongated square-pole shape formed to have a length sufficiently greater than the width of the FRP raw sheet P 1 . The holding bar  8   b  is configured to guide the cutter  8   a  in the length direction thereof. The holding bar  8   b  is arranged above the FRP raw sheet P 1  so as to cross the FRP raw sheet P 1  in the width direction thereof. The holding bar  8   b  is not limited to a square-pole shape. 
     The pair of support parts  8   c  movably support both end portions of the holding bar  8   b  so as to set the angle of the holding bar  8   b  with respect to the FRP raw sheet P 1  to a predetermined angle. In the present disclosure, the support parts  8   c  support the holding bar  8   b  such that the holding bar  8   b  crosses the orientation direction of the FRP raw sheet P 1 , that is, the length direction of the FRP raw sheet P 1 , at 45° (−45°). 
     The cutter  8   a  moves in the length direction of the holding bar  8   b,  so that the cutter  8   a  cuts the FRP raw sheet P 1  in the width direction thereof at an angle of 45° (−45°). Here, the symbol “−” of −45° denotes that the orientation direction of the reinforcing fiber F is shifted clockwise as shown in  FIG. 3 . Therefore, if the orientation direction is shifted counterclockwise, it is denoted by a symbol “+”. 
     As shown in  FIG. 4 , the pair of support parts  8   c  are configured to change the angle of the holding bar  8   b  with respect to the FRP raw sheet P 1  into an arbitrary angle. That is, the holding bar  8   b  is configured such that both ends of the holding bar  8   b  move in opposite directions parallel with the length direction of support bars  8   d  with respect to the support bars  8   d  directly supporting the holding bar  8   b.    
     In this way, in the present disclosure, the angle with respect to the length direction of the FRP raw sheet P 1  (the orientation direction of the reinforcing fiber F) is variable. Therefore, the cutting device  8  can also cut the FRP raw sheet P 1  at, for example, “+30°” or “+60°” instead of performing the cutting of the FRP raw sheet P 1  at “+45°”. Furthermore, it is possible to cut at “−45°” or the like. 
     The cutting device  8  is controlled by a control device (not shown) such that the drive for the cutter  8   a  is linked to the operation of the transfer device  6   b  of the feeding device  6 . That is, while the transfer operation for the FRP raw sheet P 1  by the transfer device  6   b  is temporarily stopped, the cutter  8   a  is driven to cut the FRP raw sheet P 1  at a predetermined angle, and the FRP sheet P 2  having a parallelogram shape as shown in  FIG. 3  is formed. The length of the side indicated by the reference sign L 1  in  FIG. 3  is equal to √2 times the width of the FRP raw sheet P 1 . 
     As shown in  FIG. 1 , a transfer device  9  that places the FRP sheet P 2  on the FRP raw sheet P 1  traveling on the main conveyance path  3  is provided on the downstream side of the cutting device  8 . As shown in  FIG. 2 , the transfer device  9  includes a holding part  9   a  that suction-holds the FRP sheet P 2 , and a moving part  9   b  that rotates the holding part  9   a  in a horizontal plane to set the direction of the reinforcing fiber F of the FRP sheet P 2  to a predetermined direction. 
     The holding part  9   a  is configured to detachably hold the FRP sheet P 2  by suction to be described later. The moving part  9   b  is formed of robot arms, has a plurality of rotation axes and is configured to move the holding part  9   a  in horizontal X and Y directions, to rotate the holding part  9   a  around the axes and to lift and lower the holding part  9   a.    
     With such a configuration, the transfer device  9  holds, by the holding part  9   a,  the FRP sheet P 2  having a parallelogram shape cut by the cutting device  8 , moves the held FRP sheet P 2  onto the main conveyance path  3  by the moving part  9   b,  and thereafter detaches the FRP sheet P 2  from the holding part  9   a  to place the FRP sheet P 2  on the FRP raw sheet P 1 . 
     As shown in  FIG. 3 , the moving part  9   b  rotates the FRP sheet P 2  and places it on the FRP raw sheet P 1  such that the orientation direction of the reinforcing fiber F of the FRP sheet P 2  is set to a predetermined direction, that is, the orientation direction is set to +45° that is an angle different from the orientation direction of the reinforcing fiber F of the FRP raw sheet P 1 . At the time the placement of the FRP sheet P 2  is performed, the FRP sheet P 2  is positioned such that cutting edges L 2  of the FRP sheet P 2  are disposed on the side edges of the FRP raw sheet P 1 . 
     As shown in  FIGS. 1 and 2 , the welding device  11  is provided in the main conveyance path  3 . The welding device  11  heats a space between the front end and the rear end of the FRP sheets P 2  placed on the FRP raw sheet P 1  and the vicinity thereof. As the welding device  11 , for example, an ultrasonic-welding machine can be used. The welding device  11  melts the resins of the FRP sheets P 2  and the FRP raw sheet P 1  below them to weld the FRP sheets P 2  on front and rear on each other, and at the same time, to weld the FRP sheets P 2  on the FRP raw sheet P 1 . As the welding device  11 , it is possible to use a structure of rolling a heated roller or a structure of pressing an elongated heater wire thereon instead of the ultrasonic-welding machine. 
     A feeding device  12  is arranged in a further downstream area than the welding device  11 . The feeding device  12  is disposed above the main conveyance path  3 . The feeding device  12  is configured to send out another FRP raw sheet P 3  onto a laminate of the FRP raw sheet P 1  and the FRP sheet P 2  traveling on the main conveyance path  3 . As shown in  FIG. 3 , the FRP raw sheet P 3  has an orientation direction of the reinforcing fiber F, which is 0°, similar to the FRP raw sheet P 1 . 
     As shown in  FIG. 2 , the feeding device  12  includes an unrolling device  12   a  that unrolls the FRP raw sheet P 3  from a state wound in a roll, and a transfer device  12   b  that transfers the FRP raw sheet P 3  unrolled by the unrolling device  12   a  onto the main conveyance path  3 . The transfer device  12   b  is configured to transfer the FRP raw sheet P 3 , which has been unrolled by the unrolling device  12   a  and has been sent out upward temporarily, downward from above using a plurality of rollers  12   c  and to send out the FRP raw sheet P 3  onto the above laminate travelling on the main conveyance path  3 . 
     As shown in  FIGS. 1 and 2 , a welding device  13  is arranged in a further downstream area than the feeding device  12 . The welding device  13  has a configuration similar to the welding device  11  and welds and unites the FRP raw sheet P 3  being the uppermost layer and the laminate of the FRP raw sheet P 1  and the FRP sheet P 2  below it. In addition, for example, if a welding device  21  to be described later arranged in a further downstream area can weld all of the four sheets shown in  FIG. 3  (the FRP raw sheet P 1 , the FRP sheet P 2 , the FRP raw sheet P 3 , and the FRP sheet P 4 ), the welding device  13  may be omitted. 
     As shown in  FIG. 1 , the second FRP sheet-forming section  14  is arranged in a further downstream area than the welding device  13 . The second FRP sheet-forming section  14  is configured to be substantially similar to the first FRP sheet-forming section  5  and includes a feeding device  15  that sends out an FRP raw sheet P 1  from a state wound in a roll, a sub-conveyance path  16  that causes the FRP raw sheet P 1  sent out from the feeding device  15  to travel, and a cutting device  17  that cuts the FRP raw sheet P 1  having traveled on the sub-conveyance path  16  in a width direction thereof at a predetermined angle. 
     The feeding device  15  includes an unrolling device  15   a  that unrolls the FRP raw sheet P 1  from a state wound in a roll, and a transfer device  15   b  that transfers the FRP raw sheet P 1  unrolled by the unrolling device  15   a  onto the sub-conveyance path  16 . The transfer device  15   b  includes a pair of rollers  15   c  arranged in upper and lower, and a drive source  15   d  such as a motor connected to either one roller  15   c  of the pair of rollers  15   c  to rotate the roller  15   c.    
     The cutting device  17  cuts the FRP raw sheet P 1  having traveled on the sub-conveyance path  16  in a width direction thereof at a predetermined angle, similar to the cutting device  8  of the first FRP sheet-forming section  5 . However, the cutting device  17  is configured to cut the FRP raw sheet P 1  in the width direction at an angle of −45° to form the FRP sheet P 4  shown in  FIG. 3 . The length of the side indicated by the reference sign L 3  in  FIG. 3  is equal to √2 times the width of the FRP raw sheet P 1 . 
     The FRP sheet P 4  is picked up by a transfer device  18 . As shown in  FIG. 2 , the transfer device  18  includes a holding part  18   a  that suction-holds the FRP sheet P 4 , and a moving part  18   b  that rotates the holding part  18   a  in a horizontal plane to set the direction of the reinforcing fiber F of the FRP sheet P 4  to a predetermined direction. 
     The transfer device  18  places the FRP sheet P 4  on the FRP raw sheet P 3  (the laminate) such that the direction of the reinforcing fiber of the FRP sheet P 4  is an angle of −45° that is different from the direction (orientation) of the reinforcing fiber F of the FRP raw sheet P 1 , the FRP sheet P 2  and the FRP raw sheet P 3 . At the time the placement of the FRP sheet P 4  is performed, the FRP sheet P 4  is positioned such that cutting edges L 4  of the FRP sheet P 4  are disposed on the side edges of the FRP raw sheet P 1 . 
     As shown in  FIG. 1 , the welding device  20  is provided slightly further downstream than the sub-conveyance path  16  in the main conveyance path  3 . The welding device  20  has a configuration substantially similar to the welding device  11 , welds the FRP sheets P 4  together disposed in front and rear, and welds and unites these FRP sheets P 4  and the laminate (the FRP raw sheet P 3 ) below them. 
     Another welding device  21  is provided further downstream than the welding device  20 . The welding device  21  welds the FRP sheet P 4  being the uppermost layer and the laminate (the FRP raw sheet P 3 ) below it again. At this time, the welding device  21  welds the FRP sheet P 4  and the laminate in a direction intersecting with the cutting edge L 4  of the FRP sheet P 4  shown in  FIG. 3 . That is, the welding is performed at a different angle from that in the welding device  20 , whereby an obtained laminate is more firmly united. 
     The FRP sheet laminate P 5  formed in this way is cut into FRP sheet laminated products P 6  having a rectangular shape shown in  FIG. 1  by a cutting device  22  provided further downstream than the transfer device  4 . The FRP sheet laminated products P 6  are sequentially stored in a storage box  23  disposed further downstream than the main conveyance path  3  as shown in  FIG. 2  and are supplied to a next process. For example, in the next process, the FRP sheet laminated product P 6  is put into a roller press machine and is cut into an appropriate shape, and a plurality of obtained shaped products of the FRP sheet laminated products P 6  are stacked to form a desired three-dimensional shape. 
     Next, the sheet space-detecting device  10  provided in the FRP sheet-laminating device  1  having the above configuration will be described with reference to  FIGS. 5 to 11B . In the following description, the sheet space-detecting device  10  provided in the welding device  11  described above will be described, but the sheet space-detecting device  19  provided in the welding device  20  described above also has a configuration similar to the sheet space-detecting device  10 . 
       FIG. 5  is a plan view schematically showing the arrangement of the FRP sheets P 2  of the present disclosure. 
     As shown in  FIG. 5 , the FRP sheets P 2  are continuously arranged with almost no space therebetween in the front-rear direction on the FRP raw sheet P 1 . Of the FRP sheets P 2 , the front end  51  and the rear end  52  of a first FRP sheet  50  (a first fiber reinforced plastic sheet) preceding in the flow direction (hereinafter, referred to as the sheet flow direction) of the main conveyance path  3  are inclined at +45° with respect to the FRP raw sheet P 1  (the length direction of the FRP raw sheet P 1 ). In addition, the front end  61  and the rear end  62  of a second FRP sheet  60  (a second fiber reinforced plastic sheet) following the first FRP sheet  50  in the sheet flow direction are inclined at +45° with respect to the FRP raw sheet P 1  (the length direction of the FRP raw sheet P 1 ). 
     The first FRP sheet  50  and the second FRP sheet  60  are arranged with a space S between the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60 . The space S has a size such that the rear end  52  of the first FRP sheet  50  does not overlap the front end  61  of the second FRP sheet  60 . The space S extends at approximately +45° with respect to the FRP raw sheet P 1 . Moreover, the orientation direction (the length direction) of the reinforcing fiber F of the first FRP sheet  50  and the second FRP sheet  60  is substantially parallel to the space S (the extending direction of the space S). 
       FIG. 6  is a front view of the sheet space-detecting device  10  and the welding device  11  of the present disclosure viewed in the sheet flow direction.  FIG. 7  is a plan view schematically showing the position of a light-detecting sensor  30  and the shape of a spacer  40  of the present disclosure. 
     Note that the plan view is a view viewed in a direction perpendicular to the plate surface of the FRP raw sheet P 1  or the FRP sheet laminate P 5 . 
     As shown in  FIG. 6 , the welding device  11  includes a heater  11  a that heats the space S and the vicinity thereof, a lifting mechanism  11   b  that lifts and lowers the heater  11   a,  and a moving mechanism  11   c  that moves the heater  11   a  and the lifting mechanism  11   b  along the space S. 
     The sheet space-detecting device  10  includes the optical light-detecting sensor  30  that detects the space S, and the spacer  40  interposed between the FRP raw sheet P 1  and the FRP sheet P 2 . The light-detecting sensor  30  is supported by a slider mechanism  34 . The slider mechanism  34  moves between a position right above the side end of the FRP raw sheet P 1  and a position outside the FRP raw sheet P 1  (outside in plan view) as shown by the arrows in  FIG. 6 . A pair of light-detecting sensors  30  are provided and project detection light  30   a  at both side ends of the space S as shown in  FIG. 7 . 
     The light-detecting sensor  30  projects the detection light  30   a  onto an area including the rear end  52  of the first FRP sheet  50 , the front end  61  of the second FRP sheet  60 , and the FRP raw sheet P 1  (the reference surface) exposed from the space S and receives the reflected light thereof. The light-detecting sensor  30  detects a step (edge) of the sheet from, for example, a change in light amount of the reflected light and detects the space S based on the step of the sheet. As such a light-detecting sensor  30 , for example, a two-dimensional laser displacement sensor can be appropriately adopted. Noted that the number of detection points for the step (edge) of the sheet is not only one but may also be two or more. 
     As shown in  FIG. 7 , a pair of spacers  40  are also provided corresponding to the light-detecting sensors  30 . The spacer  40  is formed into a plate shape and is inserted under each of two side ends of the FRP sheet P 2 . In the following description, a direction perpendicular to the plate surface of the spacer  40  may be referred to as an up-down direction, a plate surface of the spacer  40  facing the FRP raw sheet P 1  (the reference surface) may be described as a lower surface, and a plate surface of the spacer  40  facing (supporting) the FRP sheet P 2  may be described as an upper surface. The thickness of the spacer  40  in the up-down direction is twice or more the thickness of the FRP sheet P 2 , or is 5 to 10 times or more. The spacer  40  includes a first support area  41  that supports the first FRP sheet  50 , a second support area  42  that supports the second FRP sheet  60 , and a step area  43  formed between the first support area  41  and the second support area  42 . The step area  43  is an area separated downward from the first support area  41  and the second support area  42 . That is, the step area  43  is a portion depressed from the upper surface of the spacer  40  toward the lower surface thereof. 
     The first support area  41  is an area further downstream (on the left side in  FIG. 7 ) than the step area  43  in the sheet flow direction. The second support area  42  is an area further upstream (on the right side in  FIG. 7 ) than the step area  43  in the sheet flow direction. The step area  43  is provided in an area between the first support area  41  and the second support area  42 . The first support area  41  is smaller than the second support area  42  in the sheet flow direction. Further, the step area  43  is sufficiently larger than the space S in the sheet flow direction. That is, the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60  are disposed above the step area  43  with the space S. 
     The step area  43  does not extend to edges  44  of the spacer  40  parallel with the sheet flow direction. 
     In other words, the edges  44  are ends of the spacer  40  in the width direction of the FRP raw sheet P 1 , and the step area  43  is arranged apart from the edges  44 . 
     The step area  43  of the present disclosure is a through-hole  43 A that penetrates the spacer  40  in the up-down direction, and part of the first support area  41  and part of the second support area  42  are connected together. 
     Note that, as a modification of the step area  43 , a step area may extend to either one of the edges  44  of the spacer  40  and may have a shape such as a notch. In addition, the step area  43  may extend to both side ends of the spacer  40 , and the spacer  40  may have a shape divided (separated) into the first support area  41  and the second support area  42  by the step area  43 . 
     The spacer  40  is connected to a moving device  45 . The moving device  45  retracts the spacer  40  from the light-projected area of the detection light  30   a.  The moving device  45  includes a cylinder or the like that linearly moves, and retracts the spacer  40  toward upstream in the sheet flow direction. As shown by the arrow in  FIG. 7 , the spacer  40  moves by the moving device  45  between a position where the detection light  30   a  passes through the step area  43  and another position where the front end of the spacer  40  retracts further upstream than the detection light  30   a  (specifically, a position that the welding by the welding device  11  does not affect). Further, the spacer  40  may be connected to a moving device (not shown) that allows the spacer  40  to escape in a direction orthogonal to the sheet flow direction, for example, when the cutting angle for the FRP raw sheet P 1  is switched between “+45°” and “−45°”. 
       FIG. 8  is a front view of the sheet space-detecting device  10  viewed in the sheet flow direction when the welding device  11  of the present disclosure performs welding. 
     As shown in  FIG. 8 , at the time the welding device  11  performs welding, the light-detecting sensor  30  retracts outward of the FRP raw sheet P 1 , and the spacer  40  retracts upstream in the sheet flow direction. A reference sign  33  shown in  FIG. 8  represents a holding part that holds down the FRP sheet P 2  when the welding device  11  performs welding. The holding part  33  is formed into a rod shape that holds down a front end portion of the second FRP sheet  60  excluding the front end  61  thereof as shown in  FIGS. 9A to 9C  to be described later. 
     The holding part  33  holds down a front end portion other than the front end  61  of the second FRP sheet  60 . The front end portion denotes a portion adjacent to the rear side of the front end  61 . 
     The holding part  33  is provided with a guide  33   a  into which the second FRP sheet  60  is drawn. The guide  33   a  is a tapered surface provided at the lower end on the upstream side of the holding part  33  and inclines from the upper surface to the lower surface as it goes downstream. The holding part  33  is longer than the front end  61  of the second FRP sheet  60  and is arranged in inclining at a predetermined angle (+45°) with respect to the main conveyance path  3 . The holding part  33  is connected to a drive unit (not shown) and is configured to be able to lift and lower. Note that the holding part  33  may have no drive unit, be positioned so as to be able to lift and lower, and be configured to press the front end portion of the second FRP sheet  60  by its own weight. 
     A reference sign  32  shown in  FIGS. 9A to 9C  represents a holding part that holds down a rear end portion of the first FRP sheet  50  excluding the rear end  52  thereof. 
     The holding part  32  holds down a rear end portion other than the rear end  52  of the first FRP sheet  50 . The rear end portion denotes a portion adjacent to the front side of the rear end  52 . 
     The holding part  32  is also longer than the rear end  62  of the first FRP sheet  50  and is arranged to incline at a predetermined angle (+45°) with respect to the main conveyance path  3 . The holding part  32  is connected to a drive unit (not shown) and is configured to be able to lift and lower. Note that the holding part  33  may also have no drive part, be positioned so as to be able to lift and lower, and be configured to press the rear end portion of the first FRP sheet  50  by its own weight. 
     Next, the operation of the sheet space-detecting device  10  (a sheet space-detecting method) and the operation of the welding device  11  (a sheet-welding method) configured as described above will be described with reference to  FIGS. 9A to 11B . The operation of the sheet space-detecting device  10  and the operation of the welding device  11  are controlled by a control device (not shown). 
     The control device includes a CPU (Central Processing Unit), a memory such as a RAM (Random Access Memory) and a ROM (Read Only Memory), a storage device such as an SSD (Solid State Drive) and an HDD (Hard Disk Drive), and the like. 
       FIGS. 9A to 11B  are side views schematically showing the operation of the sheet space-detecting device  10  and the operation of the welding device  11  of the present disclosure. 
     In this method, first, when the space S between the rear end  52  of the first FRP sheet  50  and the front end  61  of the following second FRP sheet  60  is detected, the spacer  40  is disposed (a spacer-disposing step). In the spacer-disposing step, first, as shown in  FIG. 9A , the first FRP sheet  50  is supported by the first support area  41  of the spacer  40 , and the rear end  52  of the first FRP sheet  50  is disposed above the step area  43  (a first step). Also, the front end  61  of the second FRP sheet  60  is supported by the second support area  42  of the spacer  40 . 
     That is, in the spacer-disposing step, the spacer  40  is disposed such that the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60  are separated from the FRP raw sheet P 1 . 
     Next, as shown in  FIG. 9B , the front end  61  of the second FRP sheet  60  is disposed above the step area  43  so as to be apart from the rear end  52  of the first FRP sheet  50  (a second step). Note that in the second step, it is appropriate that the front end  61  of the second FRP sheet  60  be disposed above the step area  43  with a space greater than the proper space S shown in  FIG. 5  (for example, a space greater than the space S by about 10% to 50% thereof). Accordingly, the front end  61  of the second FRP sheet  60  is reliably prevented from overlapping the rear end  52  of the first FRP sheet  50 . In the second step, since the transfer device  9  moves the second FRP sheet  60 , the holding part  33  disposed on the upstream side may be lifted up. The holding part  32  disposed on the downstream side may be lowered. Further, in the second step, in order to adjust the entire space S, the transfer device  9  may move the second FRP sheet  60  not only in translation but also in rotation. 
     After the spacer-disposing step, in this method, as shown in  FIG. 9C , the detection light  30   a  is projected on an area including the rear end  52  of the first FRP sheet  50 , the front end  61  of the second FRP sheet  60 , and the FRP raw sheet P 1  (the reference surface) exposed from the space S, and the reflected light thereof is received (a light-detecting step). Here, in at least the light-projected area on which the detection light  30   a  is projected, the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60  are supported by the spacer  40  in a state where they are separated from the FRP raw sheet P 1  (the reference surface). 
     In other words, in an area including at least the light-projected area on which the detection light  30   a  is projected, the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60  are supported by the spacer  40  in a state where they are separated from the FRP raw sheet P 1  (the reference surface). 
     Note that in the light-detecting step, it is appropriate to lower the holding part  33  on the upstream side because the space S can be stably detected, but the holding part  33  disposed on the upstream side may be lifted up as long as the transfer device  9  holds the second FRP sheet  60 . 
     The spacer  40  limits the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60  from coming into contact with the FRP raw sheet P 1 . Accordingly, the light-detecting sensor  30  can easily detect a step (edge) of the sheet, and as a result, the space S can be detected with high accuracy. In addition, as shown in  FIG. 5 , in a case where the orientation direction of the reinforcing fiber F of the first FRP sheet  50  and the second FRP sheet  60  is parallel to the space S, the rear end  52  and the front end  61  having low tensile strength or toughness are particularly easy to hang down, the reinforcing fiber F easily fluffs thereat, and therefore a great effect is obtained by disposing the spacer  40 . 
     After the light-detecting step, in this method, as shown in  FIG. 10A , the position of the second FRP sheet  60  with respect to the first FRP sheet  50  is corrected (a sheet position-correcting step). In the sheet position-correcting step, the space S detected by the light-detecting sensor  30  is compared with the space S having an appropriate size shown in  FIG. 5 , and according to a difference therebetween, the second FRP sheet  60  is moved by the transfer device  9 . Note that it is appropriate to retract the spacer  40  from the light-projected area of the detection light  30   a  at the time after the light-detecting step and before the sheet position-correcting step or at the time after the sheet position-correcting step. When the spacer  40  is retracted, it is appropriate to lift up the holding part  32  holding down the rear end portion of the first FRP sheet  50  at the first support area  41 . Further, in the light-detecting step shown in  FIG. 9C , if the holding part  33  disposed on the upstream side is lowered, it is appropriate to lift up the holding part  33 . 
     After the sheet-correcting step, in this method, as shown in  FIG. 10B , the rear end portion of the first FRP sheet  50  excluding the rear end  52  is held down by the holding part  32 , and the front end portion of the second FRP sheet  60  excluding the front end  61  is held down by the holding part  33  (a sheet-positioning step). 
     That is, the rear end portion other than the rear end  52  of the first FRP sheet  50  is held down by the holding part  32 , and the front end portion other than the front end  61  of the second FRP sheet  60  is held down by the holding part  33 . 
     In addition, after the front end portion of the second FRP sheet  60  is held down by the holding part  33 , the transfer device  9  can release the suction to the second FRP sheet  60  and can move to pick up a next FRP sheet P 2 . After the sheet-positioning step, in this method, as described above, the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60  are welded by the welding device  11  (a sheet-welding step). 
     Next, in this method, as shown in  FIG. 11A , in order to weld the rear end  62  of the welded second FRP sheet  60  with the next FRP sheet P 2 , the FRP raw sheet P 1  is sent downstream in the sheet flow direction, and the step area  43  of the spacer  40  is moved to a position right below the light-detecting sensor  30 . As shown in  FIG. 10B  of the previous step, at the time the spacer  40  is retracted upstream in the sheet flow direction, if a state is secured in which the rear end  62  of the second FRP sheet  60  is placed on the first support area  41  of the spacer  40 , the spacer  40  does not have to be slid into a position under the second FRP sheet  60  when the spacer  40  is returned to the original position thereof, so that the movement of the spacer  40  can be smoothly performed. When the spacer  40  is returned to the original position, it is appropriate to lift up the holding parts  32  and  33  as shown in  FIG. 11A . 
     Next, in this method, as shown in  FIG. 11B , the second FRP sheet  60  (which will be a first fiber reinforced plastic sheet) is supported by the first support area  41  of the spacer  40 , the rear end  62  of the second FRP sheet  60  is disposed above the step area  43 , and the holding part  32  is lowered to hold down the rear end portion of the second FRP sheet  60 . Next, in this method, a next FRP sheet P 2  (a third FRP sheet  70 ) is picked up by the transfer device  9 . Then, the third FRP sheet  70  (which will be a second fiber reinforced plastic sheet) is supported by the second support area  42  of the spacer  40 . 
     The subsequent operation is repetition of the flow from the step of  FIG. 9A  described above. 
     According to the present disclosure described above, when a configuration is adopted in which the sheet space-detecting device  10 , which detects the space S between the rear end  52  of the preceding first FRP sheet  50  and the front end  61  of the following second FRP sheet  60  in the main conveyance path  3 , includes: the light-detecting sensor  30  that projects the detection light  30   a  on an area including the rear end  52  of the first FRP sheet  50 , the front end  61  of the second FRP sheet  60 , and the FRP raw sheet P 1  exposed from the space S and receives the reflected light thereof; and the spacer  40  that supports the rear end  52  of the first FRP sheet  50  and the front end  61  of the second FRP sheet  60  in a state where the rear end  52  and the front end  61  are separated from the FRP raw sheet P 1  in at least the light-projected area on which the detection light is projected, it is possible to improve the detecting accuracy of the space S between front end and rear end of the FRP sheets P 2 . 
     Hereinbefore, an embodiment of the present disclosure is described with reference to the drawings, but the present disclosure is not limited to the above embodiment. The shapes, combinations and the like of the components shown in the above embodiment are examples, and various modifications can be made based on design requirements and the like within the scope of the present disclosure. 
     For example, for the spacer  40  described above, a configuration as shown in  FIG. 12  can be adopted. In the following description, the same or equivalent components as or to those of the above embodiment are represented by the same reference signs, and the descriptions thereof are simplified or omitted. 
       FIG. 12  is a side cross-sectional view schematically showing a spacer  40 A of a modification of the present disclosure. 
     As shown in  FIG. 12 , the spacer  40 A is provided with a groove  43 B as the step area  43 . The groove  43 B may extend to the edges  44  (refer to  FIG. 7 ) of the spacer  40 A. The groove  43 B has a bottom portion  43 B 1 . A direct reflection-limiting member  46  is arranged on the bottom portion  43 B 1 . The direct reflection-limiting member  46  serves as the reference surface for detecting a step (edge) of the sheet instead of the FRP raw sheet P 1  described above. 
     For the direct reflection-limiting member  46 , a member having a reflection characteristic different from that of the FRP sheet P 2  is appropriate, further a member more likely diffuse-reflecting the detection light  30   a  than the FRP sheet P 2  is appropriate, and specifically, a sheet-shaped or tape-shaped member whose reflection surface is provided with a fine uneven form is appropriate. According to this configuration, since the reflection characteristic of the reference surface for detecting a step (edge) of the sheet is different from that of the FRP sheet P 2 , it is possible to more easily detect the step (edge) of the sheet than a case where the FRP raw sheet P 1  whose material is the same as the FRP sheet P 2  is used for the reference surface. 
     A rear end portion  40   b  of the spacer  40 A is formed to more swell up than a front end portion  40   a  of the spacer  40 A. The rear end portion  40   b  is thicker than the front end portion  40   a  and has a rounded shape swelling upward. According to such a configuration, it is possible to prevent the second FRP sheet P 2  from tearing when the spacer  40 A is retracted. That is, since the orientation directions of the reinforcing fibers of the second FRP sheet P 2  are in one direction, if a portion thereof that rubs against the spacer  40 A is sharp, the spacer  40 A may enter between the reinforcing fibers and tear the second FRP sheet P 2 . If the second FRP sheet P 2  is torn, a detecting error may occur when the space is detected at the torn portion, the device may stop, and therefore, the above configuration can eliminate such a concern. 
     In the above-described present disclosure, the orientation direction of the reinforcing fiber F of the FRP sheet P 2  and the FRP sheet P 4  is particularly set to +45° or −45°, but the orientation direction may be set to, for example, +30° (−30°), +60° (−60°) or the like by adjusting the angles of the holding bars of the cutting devices  8  and  17 . 
     INDUSTRIAL APPLICABILITY 
     The present disclosure can be used for a sheet space-detecting device that detects a space between the rear end of a preceding first fiber reinforced plastic sheet and the front end of a following second fiber reinforced plastic sheet in a conveyance path for fiber reinforced plastic sheets.