Patent Publication Number: US-2021170512-A1

Title: Weld bead cutting device and weld bead cutting method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2019-222878 filed on Dec. 10, 2019, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a weld bead cutting device and a weld bead cutting method. In particular, the disclosure relates to an improvement in a weld bead cutting device and a weld bead cutting method configured to remove, by cutting, a weld bead that is generated on the outer circumference of a welding portion when annular end edges of two resin members on their open sides are butted and welded to each other. 
     2. Description of Related Art 
     Conventionally, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-188794 (JP 2002-188794 A), a liner (a pressure vessel made of resin) is produced by joining a plurality of resin members (resin molded products) to each other by welding. JP 2002-188794 A discloses that the liner is produced by heating and melting the open-side end edges of a plurality of resin liner portions having a generally cylindrical shape and then butting and welding the end edges of the liner portions to each other. A reinforcing portion (referred to as a “shell” in JP 2002-188794 A) is provided, for example, by winding carbon fibers around the outer circumference of the liner so that the strength of the liner is ensured. 
     When producing the liner, a weld bead is generated on the outer circumference of a welding portion between the liner portions. There is a possibility that the weld bead may cause breakage of the carbon fibers when winding the carbon fibers around the outer circumference of the liner. Further, when the weld bead is present, there is also a possibility that a gap may be made between the outer peripheral surface of the liner and the carbon fibers, resulting in adversely affecting the strength of a tank (a tank formed by providing the reinforcing portion on the outer circumference of the liner). 
     In view of this, the cutting machining is performed to remove the weld bead by cutting at the stage before the winding operation of the carbon fibers. As the cutting machining, the automatic cutting using a cutting unit with a lathe and so on is performed for the purpose of enhancing the work efficiency. 
     SUMMARY 
       FIG. 25  illustrates a section of a part of a liner b at a generation portion of a weld bead a (hatching representing a section is omitted). In  FIG. 25 , broken lines indicate the shapes of liner portions c, d before welding. When cutting the weld bead a, a cutting tool e is advanced toward the outer peripheral surface of the liner b (see arrow f in  FIG. 25 ) while rotating the liner b about its central axis O, and the cutting tool e is moved in the width direction of the weld bead a (the direction along the central axis O of the liner b) at a predetermined feed pitch (a predetermined feed pitch per rotation of the liner b) (see arrow g in  FIG. 25 ). 
     When the sectional shape of the weld bead a is a predetermined shape and both first and second end edges of the weld bead a in its width direction are located within a prescribed range from a cutting start position h to a cutting end position i in the feed direction of the cutting tool e (the moving direction along the width direction of the weld bead a), the weld bead a is sequentially cut in its width direction by the movement of the cutting tool e from the first end edge side toward the second end edge side of the weld bead a in its width direction so that a cutting chip (a cutting chip removed from the liner b due to cutting of a part of the weld bead a) having a predetermined sectional shape (a sectional shape according to the predetermined feed pitch) is sequentially generated. For example, at the initial time of the start of the cutting machining, in the situation where the liner b makes one rotation so that the cutting tool e is moved by one feed pitch (the situation where the cutting tool e is moved to j in  FIG. 25 ), a portion k, hatched in  FIG. 25 , of the weld bead a is removed as a cutting chip from the liner b. 
     A suction device (not illustrated) for recovering a cutting chip is disposed under the cutting tool e. The suction device includes a suction port that is open upward, and is configured to suck and recover a cutting chip by generating an air flow from the suction port toward the inside of the suction device. 
     However, there are cases where the weld bead a has a variation in its width or in the positions of the first and second end edges in its width direction, along the circumferential direction of the liner b. For example, with an increase in the size of the weld bead a due to the outside air temperature at the time of welding, or due to dimensional variation or density variation of the liner portions c, d before welding, the weld bead a is subjected to a variation in its width or in the positions of the first and second end edges in its width direction. 
       FIG. 26  illustrates a section of a part of the liner b at a generation portion of the weld bead a when the first end edge of the weld bead a on its one side (the end edge of the weld bead a on the right side in  FIG. 26 ) is largely displaced to the right side. In this case, the position of the end edge of the weld bead a on the right side is located rightward of the cutting start position h in the feed direction of the cutting tool e. That is, the position of the cutting tool e at the start of cutting the weld bead a is a position closer to the center side than the position of the first end edge of the weld bead a in its width direction so that the cutting by the cutting tool e is started from this position. In this situation, the sectional area of a cutting chip generated when the cutting by the cutting tool e is started becomes large (see a portion m hatched in  FIG. 26 ; a portion to be a cutting chip). Such a cutting chip with the large sectional area has a high rigidity and thus is not easily bent, and therefore, there is a possibility that the cutting chip may impede the suction and recovery by getting caught in the suction port of the suction device. 
     In order to avoid such a situation, it is conceivable that the range from the cutting start position h to the cutting end position i in the feed direction of the cutting tool e is set large in advance. For example, in  FIG. 26 , the position of h′ is set as a cutting start position and the position of i′ is set as a cutting end position so that even when there is a variation in the positions of the first and second end edges of the weld bead a in its width direction, it is possible to generate a cutting chip, having a predetermined sectional shape (a sectional shape that prevents a too high rigidity), from the first end edge to the second end edge of the weld bead a in its width direction. 
     However, in this case, in the situation where there is no variation in the positions of the first and second end edges of the weld bead a in its width direction, the distance in which the cutting tool e is not in contact with the weld bead a (the so-called idle distance of the cutting tool e) is prolonged so that it is difficult to shorten the machining time. 
     Even in the situation where a cutting chip with a large sectional area is generated, when the situation is such that a cutting chip generated earlier is small in sectional area and is already sucked and recovered into the suction device and further that the cutting chip is generated continuously (not broken off), even the cutting chip with the large sectional area can be easily recovered (by being pulled into the suction device by the cutting chip sucked and recovered earlier). 
     That is, in order to recover a cutting chip well, it is necessary that the cutting chip having a predetermined sectional shape (a sectional shape that prevents a too high rigidity) be generated in the situation where there is a possibility that the cutting chip is not generated continuously (there is a possibility that the cutting chip is broken off), and it is necessary that the cutting chip be generated continuously (without being broken off) in the situation where there is a possibility that the cutting chip with a large sectional area is generated. 
     The disclosure has been made in view of such circumstances, and it is an object of the disclosure to provide a weld bead cutting device and a weld bead cutting method that make it possible to generate a cutting chip that can be easily recovered. 
     A first aspect of the disclosure relates to a weld bead cutting device configured to cut a weld bead generated on an outer circumference of a welding portion when annular end edges of two resin members on open sides of the two resin members are butted and welded to each other, the weld bead cutting device configured to cut the weld bead by rotating a workpiece, formed by at least the two resin members welded to each other, about a central axis extending in a direction along a butting direction of the two resin members, and by moving a cutting tool at a predetermined feed pitch along a bead width direction being the direction along the butting direction per rotation of the workpiece. The weld bead cutting device includes a bead end edge position measuring device, a bead profile information creation part, a machining information creation part, and a cutting tool feed control part. The bead end edge position measuring device is configured to measure a position of at least one of both end edges of the weld bead in the bead width direction over an entire circumference of the workpiece in a circumferential direction of the workpiece. The bead profile information creation part is configured to, based on information on the position of the end edge of the weld bead in the bead width direction over the entire circumference of the workpiece in the circumferential direction measured by the bead end edge position measuring device, create bead profile information being information on a shape of the end edge of the weld bead over the entire circumference of the workpiece in the circumferential direction. The machining information creation part is configured to, based on the bead profile information created by the bead profile information creation part, create machining information of the workpiece per rotation of the workpiece being position information of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece so that a moving locus of the cutting tool relative to the workpiece along the circumferential direction of the workpiece approximates the shape of the end edge of the weld bead over the entire circumference of the workpiece in the circumferential direction per rotation of the workpiece rotating about the central axis. The cutting tool feed control part is configured to, according to the machining information created by the machining information creation part, control a position of the cutting tool in the bead width direction per rotation of the workpiece rotating about the central axis. 
     With this configuration, based on the information on the position of the end edge of the weld bead in the bead width direction over the entire circumference of the workpiece in the circumferential direction measured by the bead end edge position measuring device, the bead profile information over the entire circumference of the workpiece in the circumferential direction is created. Based on this bead profile information, the machining information of the workpiece per rotation of the workpiece being the position information of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece is created so that the moving locus of the cutting tool relative to the workpiece approximates the shape of the end edge of the weld bead per rotation of the workpiece. According to this machining information, the position of the cutting tool in the bead width direction per rotation of the workpiece is controlled. Therefore, the shape of a cutting chip generated by cutting can be adjusted as desired so that it is possible to generate a cutting chip having a predetermined sectional shape (a sectional shape that prevents a too high rigidity), or to generate a cutting chip that is continuous (not broken off). As a result, it is possible to generate a cutting chip that can be easily recovered. 
     In the weld bead cutting device according to the first aspect, the machining information creation part may be configured to create machining information in which the feed pitch of the cutting tool per rotation of the workpiece is set to a dimension that causes a width of a cutting chip to become equal to or less than a predetermined dimension, the cutting chip generated to have the width corresponding to the feed pitch, and in which the feed pitch of the cutting tool per rotation of the workpiece is set to be constant from a cutting start position of the cutting tool to a cutting end position of the cutting tool in the bead width direction. 
     With this configuration, in a cutting process of the weld bead by the cutting tool, the width of a cutting chip generated by moving the cutting tool from the cutting start position to the cutting end position in the bead width direction becomes equal to or less than the dimension of the feed pitch. This feed pitch is set to a dimension that causes the width of a cutting chip generated to become equal to or less than a predetermined dimension. Therefore, the width of a cutting chip can be limited so that it is possible to generate a cutting chip having a sectional shape that prevents a too high rigidity. Consequently, even in the situation where there is a possibility that a cutting chip is not generated continuously (there is a possibility that a cutting chip is broken off), it is possible to generate a cutting chip having a sectional shape that prevents a too high rigidity so that it is possible to generate a cutting chip that can be easily recovered. 
     In the weld bead cutting device according to the first aspect, the bead end edge position measuring device may be configured to measure the positions of both end edges of the weld bead in the bead width direction over the entire circumference of the workpiece in the circumferential direction; the bead profile information creation part may be configured to, based on information on the positions of both end edges of the weld bead in the bead width direction over the entire circumference of the workpiece in the circumferential direction measured by the bead end edge position measuring device, create bead profile information being information on the shapes of both end edges of the weld bead over the entire circumference of the workpiece in the circumferential direction; and the machining information creation part may be configured to create machining information in which the feed pitch of the cutting tool per phase in the circumferential direction of the workpiece is changed so that the position of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece from a cutting start position to a cutting end position in the bead width direction is located closer to a center side of the weld bead than the positions of both end edges of the weld bead per rotation of the workpiece. 
     With this configuration, by changing the feed pitch per phase in the circumferential direction of the workpiece, the position of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece from the cutting start position to the cutting end position in the bead width direction is located closer to the center side of the weld bead than the positions of both end edges of the weld bead per rotation of the workpiece. That is, the cutting tool does not straddle the end edge of the weld bead while moving from the cutting start position to the cutting end position. Therefore, even in the situation where there is a possibility that a cutting chip with a large sectional area is generated, since the cutting chip is generated continuously (not broken off), the cutting chip is, for example, pulled into a suction device by a cutting chip generated earlier. Consequently, also in this, it is possible to generate a cutting chip that can be easily recovered. 
     The weld bead cutting device according to the first aspect may further include: surface position measuring devices configured to respectively measure, along the circumferential direction, positions of outer peripheral surfaces of the two resin members on both sides of the welding portion in the direction along the butting direction; a profile machining data creation part configured to, based on information on the positions of the outer peripheral surfaces on both sides of the welding portion measured by the surface position measuring devices, create profile machining data by comparing information on the positions of the outer peripheral surfaces in a same phase in the circumferential direction and extracting the information on the position of the outer peripheral surface located on an outer peripheral side; and a cutting tool advance and retreat control part configured to, according to the profile machining data created by the profile machining data creation part or machining data obtained by correcting the profile machining data, adjust an advance-retreat position of the cutting tool relative to the outer peripheral surface of the workpiece rotating about the central axis so that a distance between the position of the outer peripheral surface per phase in the circumferential direction in the data and a position of a cutting blade of the cutting tool is maintained constant. 
     The cutting of the weld bead by adjusting the advance-retreat position of the cutting tool is applied as finish machining that is performed after the cutting is performed by moving the cutting tool in the bead width direction as described above. That is, this cutting is applied as the machining that further cuts the weld bead slightly remaining at the time of the completion of the cutting (rough machining) performed by moving the cutting tool in the bead width direction. 
     With this configuration, the cutting tool is advanced and retreated to follow the position of the outer peripheral surface of one of the two resin members (e.g. the position of the outer peripheral surface located on the outer peripheral side). When the outer peripheral surface is spaced away from the cutting tool, the cutting tool is advanced, and conversely, when the outer peripheral surface approaches the cutting tool, the cutting tool is retreated. Therefore, even when the section of the workpiece is not a perfect circle, it is possible to cut the weld bead well with high accuracy over its entirety in the circumferential direction. For example, if the tip position of the cutting blade of the cutting tool is set to align with the proximal end position of the weld bead, it is possible to remove the weld bead completely so that the level difference due to the weld bead does not occur. 
     In the weld bead cutting device according to the first aspect, the workpiece may be a liner used for a hydrogen tank. 
     Since hydrogen gas has a low molecular weight and a small atomic size, a material having a high gas barrier property is employed for the liner that is used for the hydrogen tank. This type of material has a particularly high melting point and high crystallinity, and it is difficult to mold this type of material into a predetermined shape. Further, since a variation in shrinkage factor is large in respective portions at the time of cooling after molding, it is difficult mold this type of material into a perfect circle. Even in the case of a workpiece that is molded of this type of material, the disclosure can cut a weld bead well over its entirety in the circumferential direction and thus is particularly effective. 
     A second aspect of the disclosure relates to a weld bead cutting method configured to cut a weld bead generated on an outer circumference of a welding portion when annular end edges of two resin members on open sides of the two resin members are butted and welded to each other, the weld bead cutting method configured to cut the weld bead by rotating a workpiece, formed by at least the two resin members welded to each other, about a central axis extending in a direction along a butting direction of the two resin members, and by moving a cutting tool at a predetermined feed pitch along a bead width direction being the direction along the butting direction per rotation of the workpiece. The weld bead cutting method includes a bead end edge position measuring step, a bead profile information creation step, a machining information creation step, and a cutting tool feed control step. In the bead end edge position measuring step, a position of at least one of both end edges of the weld bead in the bead width direction is measured over an entire circumference of the workpiece in a circumferential direction of the workpiece. In the bead profile information creation step, based on information on the position of the end edge of the weld bead in the bead width direction over the entire circumference of the workpiece in the circumferential direction measured by the bead end edge position measuring step, bead profile information being information on a shape of the end edge of the weld bead over the entire circumference of the workpiece in the circumferential direction is created. In the machining information creation step, based on the bead profile information created by the bead profile information creation step, machining information of the workpiece per rotation of the workpiece being position information of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece is created so that a moving locus of the cutting tool relative to the workpiece along the circumferential direction of the workpiece approximates the shape of the end edge of the weld bead over the entire circumference of the workpiece in the circumferential direction per rotation of the workpiece rotating about the central axis. In the cutting tool feed control step, according to the machining information created by the machining information creation step, a position of the cutting tool in the bead width direction per rotation of the workpiece rotating about the central axis is controlled. 
     Also with this configuration, the shape of a cutting chip generated by cutting can be adjusted as desired so that it is possible to generate a cutting chip having a predetermined sectional shape (a sectional shape that prevents a too high rigidity), or to generate a cutting chip that is continuous (not broken off). As a result, it is possible to generate a cutting chip that can be easily recovered. 
     According to the disclosure, based on the bead profile information created based on the information on the position of the end edge of the weld bead in the bead width direction over the entire circumference of the workpiece in the circumferential, the machining information of the workpiece per rotation of the workpiece being the position information of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece is created so that the moving locus of the cutting tool relative to the workpiece approximates the shape of the end edge of the weld bead per rotation of the workpiece. According to this machining information, the position of the cutting tool in the bead width direction per rotation of the workpiece is controlled. Therefore, the shape of a cutting chip generated by cutting can be adjusted as desired so that it is possible to generate a cutting chip having a predetermined sectional shape, or to generate a cutting chip that is continuous. As a result, it is possible to generate a cutting chip that can be easily recovered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG. 1  is a sectional view of a tank taken along its axial direction according to an embodiment; 
         FIG. 2  is a side view illustrating a state in which a liner is set in a weld bead cutting device according to a first embodiment; 
         FIG. 3  is a plan view illustrating a state in which the liner is set in the weld bead cutting device according to the first embodiment; 
         FIG. 4  is a diagram illustrating a cutting unit and its control system in the weld bead cutting device according to the first embodiment; 
         FIG. 5  is a developed view of the surrounding of a generation portion of a weld bead in the liner; 
         FIG. 6  is a sectional view of the weld bead and its peripheral portion taken along the line VI-VI in  FIG. 5 ; 
         FIG. 7  is a sectional view of the weld bead and its peripheral portion taken along the line VII-VII in  FIG. 5 ; 
         FIG. 8  is a sectional view of the weld bead and its peripheral portion taken along the line VIII-VIII in  FIG. 5 ; 
         FIG. 9  is a diagram illustrating the sequence of a weld bead cutting process in the first embodiment; 
         FIG. 10  is a diagram for explaining relative moving loci of a cutting tool in a region A portion in  FIG. 5  in the first embodiment; 
         FIG. 11  is a diagram for explaining relative moving loci of the cutting tool in a region B portion in  FIG. 5  in the first embodiment; 
         FIG. 12  is a diagram for explaining relative moving loci of the cutting tool in a region C portion in  FIG. 5  in the first embodiment; 
         FIG. 13  is a diagram for explaining relative moving loci of the cutting tool in the region A portion in  FIG. 5  in a second embodiment; 
         FIG. 14  is a diagram for explaining relative moving loci of the cutting tool in the region B portion in  FIG. 5  in the second embodiment; 
         FIG. 15  is a diagram for explaining relative moving loci of the cutting tool in the region C portion in  FIG. 5  in the second embodiment; 
         FIG. 16  is a sectional view of a part of a liner at the time when the rough machining is finished in a third embodiment; 
         FIG. 17  is a plan view illustrating a state in which the liner is set in a weld bead cutting device according to the third embodiment; 
         FIG. 18  is a diagram illustrating a cutting unit and its control system in the weld bead cutting device according to the third embodiment; 
         FIG. 19  is a diagram for explaining pressing positions of rollers on an outer peripheral surface of the liner in the third embodiment; 
         FIG. 20  is a diagram illustrating the sequence of finish machining in the third embodiment; 
         FIG. 21  is a diagram for explaining a roller pressing process and a surface position measurement process in the third embodiment, and is a diagram taken along the line A-A in  FIG. 17 ; 
         FIG. 22  is a diagram corresponding to  FIG. 21  and illustrates a state in which the liner is rotated by 90 degrees after the start of the finish machining; 
         FIG. 23  is a diagram illustrating the relationship between the outer peripheral surface position of the liner and the tip position of a cutting blade of a cutting tool after finish machining data is subjected to offset processing; 
         FIG. 24  is a diagram corresponding to  FIG. 21  and illustrates a state in which the finish machining is completed; 
         FIG. 25  is a sectional view of a part of a liner at a generation portion of a weld bead in a related art; and 
         FIG. 26  is a sectional view of a part of the liner at a generation portion of a weld bead when the end edge of the weld bead on its one side is largely displaced in the related art. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the disclosure will be described with reference to the drawings. In this embodiment, a description will be given of a case where the disclosure is applied as a weld bead cutting device and a weld bead cutting method configured to remove, by cutting, a weld bead that is generated on the outer circumference of a liner of a resin tank. 
     Configuration of Tank 
     Before describing the weld bead cutting device and the weld bead cutting method, the configuration of the tank will be described. 
       FIG. 1  is a diagram illustrating a section of a tank  1  taken along its axial direction. As illustrated in  FIG. 1 , the tank  1  includes a tank body  2  having a sealed cylindrical shape as a whole, and caps  3 A,  3 B respectively attached to both end portions (a first side portion and a second side portion) of the tank body  2  in its longitudinal direction (axial direction). 
     The inside of the tank body  2  serves as a storage space  5  for storing gas. The tank  1  can be filled with gas at normal pressure or gas at a pressure higher than the normal pressure. For example, in a fuel cell system, fuel gas (hydrogen) filled in the tank  1  in a high pressure state is reduced in pressure and supplied for power generation in the fuel cell. 
     The tank body  2  includes a liner  11  (an inner shell) and a reinforcing portion  12  (an outer shell). The liner  11  is made of a resin material excellent in gas barrier property (a multilayer material containing an ethylene vinyl alcohol material, a nylon material, or the like). The reinforcing portion  12  is made of fiber reinforced plastic (so-called FRP) containing carbon fibers and epoxy resin, and is formed by being wound around the outer circumference of the liner  11 . 
     The caps  3 A,  3 B are made of metal such as stainless steel and are each provided at the center of a hemispherical end wall portion of the tank body  2 . A female screw (not illustrated) is formed on the inner peripheral surface of each of openings  31   a,    31   b  respectively provided in the caps  3 A,  3 B. Consequently, a functional component such as a pipe or a valve assembly  14  can be screwed into and connected to each of the caps  3 A,  3 B through the female screw. In  FIG. 1 , a two-dot chain line illustrates an example in which the valve assembly  14  is attached to only the cap  3 B. For example, in the case of the tank  1  applied to the fuel cell system, the storage space  5  and an external gas flow passage (not illustrated) are connected to each other through the valve assembly  14  in which piping elements such as a valve and a joint are integrally assembled, and thus, hydrogen can be filled into the storage space  5  and can also be discharged from the storage space  5 . 
     The liner  11  is formed in such a way that three liner portions (resin molded products)  21 ,  22 ,  23  separated in the longitudinal direction of the liner  11  are joined to each other by infrared welding or the like. That is, the end edges of the side liner portions  22 ,  23  having a bowl shape are respectively joined to both end edges of the center liner portion  21  having a cylindrical shape by infrared welding or the like so that the hollow liner  11  is formed. In this way, the liner  11  is formed such that the annular end edges of the resin members (the liner portions  21 ,  22 ,  23 ) on their open sides are butted and welded to each other. 
     The center liner portion  21  is formed into the cylindrical shape extending with a predetermined length along the axial direction of the liner  11 . 
     The side liner portions  22 ,  23  respectively have trunk portions  22   a,    23   a  each extending with a predetermined length along the axial direction of the liner  11 . The first end side (the center liner portion  21  side) of each of the trunk portions  22   a,    23   a  in its axial direction is open. That is, this portion serves as the end edge on the open side. The side liner portions  22 ,  23  respectively have bent portions  22   b,    23   b  and communication portions  22   c,    23   c.  The bent portions  22   b,    23   b  are respectively formed at reduced-diameter end portions of the trunk portions  22   a,    23   a  on their second end sides (outer sides). The communication portions  22   c,    23   c  are respectively open at the center portions of the bent portions  22   b,    23   b.    
     The bent portions  22   b,    23   b  respectively have the functions of ensuring the strength of the side liner portions  22 ,  23 . The caps  3 A,  3 B are respectively located between the outer peripheral surfaces of the bent portions  22   b,    23   b  and the end portions of the reinforcing portion  12 . 
     Next, a description will be given of a plurality of embodiments of a weld bead cutting device  100  configured to remove, by cutting, a weld bead that is generated on the outer circumference of the liner  11 . 
     First Embodiment 
     Weld Bead Cutting Device 
       FIG. 2  is a side view illustrating a state in which the liner  11  is set in the weld bead cutting device  100 .  FIG. 3  is a plan view illustrating a state in which the liner  11  is set in the weld bead cutting device  100 . As illustrated in these figures, a workpiece (an intermediate molded product of the tank  1  at the stage before the reinforcing portion  12  is formed) is set in the weld bead cutting device  100 . The workpiece is in a state in which the caps  3 A,  3 B are attached to the liner  11  formed by joining the center liner portion  21  and the side liner portions  22 ,  23  to each other. Hereinafter, for convenience, the intermediate molded product will also be referred to as the liner  11 . 
     The weld bead cutting device  100  is for removing, by cutting, weld beads FB that are respectively generated on the outer circumferences of joining portions  1 A,  1 B (see  FIG. 1 ) where the center liner portion  21  and the side liner portions  22 ,  23  are joined to each other, respectively. In the following description, the longitudinal direction of the weld bead cutting device  100  (the direction along the axial direction of the liner  11  in the state where the liner  11  is set) is defined as an X-direction, the horizontal direction perpendicular to the X-direction is defined as a Y-direction, and the vertical direction is defined as a Z-direction. 
     Specifically, when the center liner portion  21  and the side liner portions  22 ,  23  are welded to each other, a part of the resin (the resin material forming the end edges of the center liner portion  21  and the side liner portions  22 ,  23 ) melted by heating flows out toward the outer peripheral side of the liner  11  and then is cooled and cured to be the weld beads FB. There is a possibility that the weld beads FB may cause breakage of the carbon fibers or the like when winding the carbon fibers or the like around the outer circumference of the liner  11  to form the reinforcing portion  12 . Further, when the weld beads FB are present, there is also a possibility that a gap may be made between the outer peripheral surface  11   a  of the liner  11  and the reinforcing portion  12 , resulting in adversely affecting the strength of the tank  1 . Therefore, it is necessary to remove the weld beads FB by cutting. 
     As described with reference to  FIG. 25 , conventionally, when cutting the weld bead a, the cutting tool e is advanced toward the outer peripheral surface of the liner b while rotating the liner b about its central axis O, and the cutting tool e is moved in the width direction of the weld bead a at a predetermined feed pitch. When the sectional shape of the weld bead a is a predetermined shape, a cutting chip k having a predetermined sectional shape (a sectional shape according to the predetermined feed pitch) is sequentially generated. However, when the weld bead a has a variation in its width or in the positions of both end edges in its width direction, along the circumferential direction of the liner b, there are cases where, as illustrated in  FIG. 26 , the position of the cutting tool e at the start of cutting the weld bead a becomes a position closer to the center side than the position of the first end edge of the weld bead a in its width direction, and in this case, the cutting by the cutting tool e is started from this position so that the sectional area of the cutting chip m becomes large. The cutting chip m with such a large sectional area has a high rigidity and thus is not easily bent, and therefore, there is a possibility that the cutting chip m may impede the suction and recovery by getting caught in the suction port of the suction device disposed under the cutting tool e. It is possible to generate a cutting chip having a predetermined sectional shape by setting the range from the cutting start position h′ to the cutting end position i′ in the feed direction of the weld bead a to be large in advance. However, with this configuration, in the situation where there is no variation in the positions of the end edges of the weld bead a in its width direction, the idle distance of the cutting tool e is prolonged so that the machining time cannot be shortened. 
     The weld bead cutting device  100  according to this embodiment is configured to facilitate the recovery of a cutting chip by generating the cutting chip having a predetermined sectional area without causing the prolongation of the machining time. A specific description will be given below. 
     As illustrated in  FIGS. 2 and 3 , the weld bead cutting device  100  includes a base stand  200 , a pair of right and left liner rotation units  300 , and a cutting unit  400 . Each of them will be described below. 
     The base stand  200  includes a base plate  201  extending in the horizontal direction, and the base plate  201  is supported by a plurality of support legs  202 . The length (the dimension in the X-direction) of the base plate  201  is set to be sufficiently longer than the length of the liner  11  in the direction along its axial direction. Further, an upper frame portion  204  is disposed above the base plate  201 . The upper frame portion  204  is supported by column portions  203  provided upright on the base plate  201 . 
     The liner rotation units  300  are for supporting the liner  11  in a transverse state (a state in which the axial direction of the liner  11  is horizontal) and for rotating the liner  11  about its central axis (rotation center). That is, the liner rotation units  300  are configured to rotate the liner  11  about the central axis extending in the direction along the butting direction (the direction in which the liner portions  21 ,  22 ,  23  are butted to each other). 
     Specifically, each of the liner rotation units  300  includes a unit body  301  that is slidable on the base plate  201 , and a rotation rod  302  protruding from the unit body  301  in the horizontal direction (the horizontal direction toward the center side of the base plate  201 ). 
     The unit body  301  is movable in the horizontal direction (the X-direction) on a rail (not illustrated) provided on the base plate  201 . A power source for sliding movement of the unit body  301  is an electric motor (not illustrated). Alternatively, the power source may be another power source. The rotation rod  302  is supported to be rotatable about the horizontal axis (about the horizontal axis in the X-direction) by a bearing (not illustrated) provided inside the unit body  301 . The rotation rod  302  is rotatable about the horizontal axis by receiving the power from an electric motor (not illustrated). The power source for rotating the rotation rod  302  may alternatively be another power source. Distal end portions of the rotation rods  302  serve as fitting portions  303  that are inserted and fitted into the openings  31   a,    31   b  (see  FIG. 1 ) provided in the caps  3 A,  3 B, respectively. The fitting portions  303  are respectively fitted into the openings  31   a,    31   b  by using so-called spigot joint. Retaining members  304  are respectively attached to the distal end portions of the rotation rods  302  for retaining the caps  3 A,  3 B to disable the rotation of the caps  3 A,  3 B relative to the rotation rods  302 , respectively. By the retaining members  304 , the end portions (the caps  3 A,  3 B) of the liner  11  are retained so that the end portions of the liner  11  are prevented from rotating relative to the rotation rods  302 , respectively. By the rotation of the rotation rods  302  in this retaining state, the rotational forces are transmitted to the liner  11  to rotate the liner  11  about the horizontal axis (about the horizontal axis in the X-direction). The support structure of the liner  11  by the rotation rods  302  is not limited to that described above. 
     The cutting unit  400  is for removing the weld beads FB by cutting.  FIG. 4  is a diagram illustrating the cutting unit  400  and its control system.  FIG. 4  is a diagram as viewed from arrow B in  FIG. 3 . 
     As illustrated in  FIGS. 3 and 4 , the cutting unit  400  is configured such that a first slider  420  and a second slider  430  are supported on a unit stand  410  so that the first slider  420  and the second slider  430  are slidable relative to each other. The unit stand  410  is slidable along the X-direction. 
     The first slider  420  is supported by rails  411  provided on the unit stand  410  and extending along the Y-direction. The first slider  420  is slidable on the rails  411  along the Y-direction. The second slider  430  is supported by rails  421  provided on the first slider  420  and extending along the X-direction. The second slider  430  is slidable on the rails  421  along the X-direction. Power sources for sliding movements of the sliders  420 ,  430  are each an electric motor (not illustrated). Alternatively, the power source may be another power source. 
     A cutting tool  441  for cutting the weld bead FB is detachably attached to a distal end portion (a distal end portion on the liner  11  side) of the second slider  430 . A well-known bit is employed as the cutting tool  441 . 
     The cutting unit  400  is provided with a distance sensor  600  that moves integrally with the sliding movement (the sliding movement in the X-direction) of the unit stand  410 . The distance sensor  600  is disposed above the cutting tool  441  and faces the outer peripheral surface of the liner  11 . The distance sensor  600  is formed by an optical sensor or an ultrasonic sensor and is a non-contact sensor that measures both end positions of the weld bead FB in its width direction. For example, when the distance sensor  600  is used as a laser displacement meter, a light emitter and a light receiver are built in, and in the state where the liner  11  is rotated about the horizontal axis, laser light is sequentially irradiated from the light emitter over the entire circumference (over the phases in the rotation direction) of the weld bead FB and its peripheral portion in its circumferential direction (the circumferential direction of the liner  11 ), and the time from the irradiation of the laser light until the laser light is reflected by the surface of the liner  11  or the weld bead FB and received by the light receiver is measured, thereby measuring the shape of the surrounding of the weld bead FB. 
     Specifically, in the laser light irradiated from the distance sensor  600 , the time from the irradiation until the reception by the light receiver becomes relatively long for the laser light irradiated on the surface of the liner  11  (a portion other than the generation portion of the weld bead FB), and the time from the irradiation until the reception by the light receiver becomes relatively short for the laser light irradiated on the generation portion of the weld bead FB due to the weld bead FB projecting from the surface of the liner  11 . Accordingly, by measuring the time difference, it is possible to measure the shape of the weld bead FB, particularly the positions of the end edges of the weld bead FB in its width direction. 
       FIG. 5  is a developed view of the surrounding of the generation portion of the weld bead FB in the liner  11 .  FIGS. 6 to 8  illustrate sections of respective portions when the weld bead FB has a variation in its width or in the positions of both end edges in its width direction. Specifically,  FIG. 6  is a sectional view of the weld bead FB and its peripheral portion taken along the line VI-VI in a region A portion in  FIG. 5 . In this portion, the weld bead FB is larger than an adequate shape.  FIG. 7  is a sectional view of the weld bead FB and its peripheral portion taken along the line VII-VII in a region B portion in  FIG. 5 . In this portion, the weld bead FB has a shape displaced to the right in the figure compared to the adequate shape.  FIG. 8  is a sectional view of the weld bead FB and its peripheral portion taken along the line VIII-VIII in a region C portion in  FIG. 5 . In this portion, the weld bead FB is smaller than the adequate shape. 
     According to the measurement operation of the position of the end edge of the weld bead FB in its width direction by the distance sensor  600 , in the phase (the phase in the circumferential direction of the liner  11 ) of the section illustrated in  FIG. 6 , P 1  in the figure is measured as a position of a first end edge (the end edge on the right side in the figure) of the weld bead FB in its width direction, and P 2  in the figure is measured as a position of a second end edge (the end edge on the left side in the figure) of the weld bead FB in its width direction. In the phase of the section illustrated in  FIG. 7 , P 3  in the figure is measured as a position of the first end edge of the weld bead FB in its width direction, and P 4  in the figure is measured as a position of the second end edge of the weld bead FB in its width direction. In the phase of the section illustrated in  FIG. 8 , P 5  in the figure is measured as a position of the first end edge of the weld bead FB in its width direction, and P 6  in the figure is measured as a position of the second end edge of the weld bead FB in its width direction. In the measurement operation of the position of the end edge of the weld bead FB in its width direction by the distance sensor  600 , the irradiation width of the light from the light emitter is prescribed so that the shape of the weld bead FB (the positions of the end edges of the weld bead FB in its width direction) can be measured by one rotation of the liner  11 . By setting as a reference phase one of the phases in the circumferential direction of the liner  11 , each of the phases and the positions of the first end edge and the second end edge of the weld bead FB in its width direction per phase are measured to be correlated with each other, and the information on the positions of the first end edge and the second end edge of the weld bead FB in its width direction per phase is output from the distance sensor  600 . 
     As illustrated in  FIG. 4 , a suction device  700  is disposed under the cutting tool  441  in the cutting unit  400 . The suction device  700  includes a suction port  701  that is open upward, and is configured to suck and recover a cutting chip of the weld bead FB (a cutting chip removed from the liner  11  due to cutting of a part of the weld bead FB by the cutting tool  441 ) by generating an air flow from the suction port  701  toward the inside of the suction device  700 . 
     The weld bead cutting device  100  is provided with a controller  500  for controlling the sliding movements of the sliders  420 ,  430 . Although not illustrated, the controller  500  includes a generally-known central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and so on. A control program and so on for controlling a cutting operation (a cutting process) of the weld bead FB are stored in the ROM. The CPU performs calculation processing based on the control program stored in the ROM. 
     The controller  500  includes a cutting unit advance and retreat control part  510  for controlling the sliding movement of the first slider  420 , and a cutting tool feed control part  520  for controlling the sliding movement of the second slider  430 . 
     The controller  500  further includes a bead end edge position information acquisition part  530 , a bead width calculation part  540 , a bead profile information creation part  550 , and a machining information creation part  560 . 
     When the first slider  420  is caused to slide by the control by the cutting unit advance and retreat control part  510 , since the second slider  430  is placed on the first slider  420 , the sliders  420 ,  430  slide integrally in the Y-direction. 
     When the second slider  430  is caused to slide by the control by the cutting tool feed control part  520 , the second slider  430  slides in the X-direction (slides relative to the first slider  420 ). This sliding movement causes the cutting tool  441  to slide in the X-direction. 
     By receiving an output signal from the distance sensor  600 , the bead end edge position information acquisition part  530  acquires the information on the positions of the first end edge and the second end edge of the weld bead FB in its width direction per phase. This position information is, for example, information on the distances from a reference point in the direction along the central axis of the liner  11  to the positions of both end edges of the weld bead FB in its width direction. For example, information on the distance from one of the end edges of the liner  11  in its longitudinal direction to the first end edge of the weld bead FB in its width direction, and information on the distance from the one of the end edges of the liner  11  in its longitudinal direction to the second end edge of the weld bead FB in its width direction are acquired per phase at every predetermined angle (e.g. every 1°) in the circumferential direction of the liner  11 . That is, in the phase of the section illustrated in  FIG. 6 , the distance from the reference point (e.g. the right end edge of the liner  11  in its longitudinal direction) to P 1  in the figure is acquired as information on the position of the first end edge (the end edge on the right side in the figure) of the weld bead FB in its width direction, and the distance from the reference point to P 2  in the figure is acquired as information on the position of the second end edge (the end edge on the left side in the figure) of the weld bead FB in its width direction. Likewise, in the phase of the section illustrated in  FIG. 7 , the distance from the reference point to P 3  in the figure is acquired as information on the position of the first end edge of the weld bead FB in its width direction, and the distance from the reference point to P 4  in the figure is acquired as information on the position of the second end edge of the weld bead FB in its width direction. Further, in the phase of the section illustrated in  FIG. 8 , the distance from the reference point to P 5  in the figure is acquired as information on the position of the first end edge of the weld bead FB in its width direction, and the distance from the reference point to P 6  in the figure is acquired as information on the position of the second end edge of the weld bead FB in its width direction. 
     The bead width calculation part  540  calculates the dimension of the weld bead FB in its width direction per phase at every predetermined angle (e.g. every) 1 ° in the circumferential direction of the liner  11 . This calculation is performed by subtracting the distance between the reference point and the first end edge of the weld bead FB in its width direction from the distance between the reference point and the second end edge of the weld bead FB in its width direction per phase. The bead width calculation part  540  also calculates the center position of the weld bead FB in its width direction per phase. This calculation is performed by calculating the average value of the distance between the reference point and the first end edge of the weld bead FB in its width direction and the distance between the reference point and the second end edge of the weld bead FB in its width direction per phase. The center position thus calculated serves as information on the center position of the movement range of the cutting tool  441  per phase in the cutting machining of the weld bead FB which will be described later. 
     The bead profile information creation part  550  obtains the shapes of both side edges (both side edges extending in the circumferential direction of the liner  11 ) of the weld bead FB by connecting, in the circumferential direction of the liner  11 , the positions (the positions in the respective phases) of both end edges of the weld bead FB in its width direction acquired by the bead end edge position information acquisition part  530 . A specific description will be given below with reference to  FIG. 10  being an enlarged view of the weld bead FB in the region A portion in  FIG. 5 . In the respective phases (a 1  to a 5  in  FIG. 10 ) in the circumferential direction of the liner  11 , the positions of the end edge of the weld bead FB on the right side are points a 1 , b 1 , c 1 , d 1 , e 1  in the figure. The shape (the bead profile) of the end edge of the weld bead FB on the right side is obtained by connecting these points in the circumferential direction of the liner  11 . Likewise, in the respective phases in the circumferential direction of the liner  11 , the positions of the end edge of the weld bead FB on the left side are points a 2 , b 2 , c 2 , d 2 , e 2  in the figure. The shape (the bead profile) of the end edge of the weld bead FB on the left side is obtained by connecting these points in the circumferential direction of the liner  11 . 
     When obtaining the bead profile, it is preferable that the points a 1 , b 1 , c 1 , d 1 , e 1  (a 2 , b 2 , c 2 , d 2 , e 2 ) in the respective phases be connected to each other in the circumferential direction of the liner  11  by a smooth curved line. That is, with respect to the points a 1 , b 1 , c 1 , d 1 , e 1  (a 2 , b 2 , c 2 , d 2 , e 2 ), the adjacent points present on both sides (both sides in the circumferential direction of the liner  11 ) are interpolated so that it is possible to calculate positions that connect between these points by a smooth curved line. 
     According to the bead profile information on the end edges of the weld bead FB created by the bead profile information creation part  550 , the machining information creation part  560  creates position information of the cutting tool  441  in its feed direction (the direction along the width direction of the weld bead FB) for use when cutting the weld bead FB by the cutting tool  441 . 
     Specifically, using the bead profile information on one of the sides (e.g. on the right side) out of the bead profile information on both end edges of the weld bead FB, information defining the position of the cutting tool  441  in its feed direction per phase is created so as to obtain a cutting locus (a moving locus) that approximates (approximately coincides with) the shape of the end edge of the weld bead FB along the circumferential direction of the liner  11  being this bead profile information. This information is also created as information defining the position of the cutting tool  441  in its feed direction (the position of the cutting tool  441  in its feed direction per rotation of the liner  11 ) per phase so that even in the state where the cutting tool  441  is moved in the width direction by a predetermined feed pitch per rotation of the rotating liner  11 , the cutting locus (the cutting locus that approximately coincides with the shape of the end edge of the weld bead FB along the circumferential direction of the liner  11 ) is obtained. 
     This information creation operation corresponds to an operation of “creating, based on the bead profile information created by the bead profile information creation part, machining information of the workpiece per rotation of the workpiece being position information of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece so that a moving locus of the cutting tool relative to the workpiece along the circumferential direction of the workpiece approximates the shape of the end edge of the weld bead over the entire circumference of the workpiece in the circumferential direction per rotation of the workpiece rotating about the central axis” referred to in the disclosure. 
     The feed pitch set herein is set in advance by experiments or simulations as a value that enables the generation of a cutting chip having a predetermined sectional shape (a sectional shape that prevents a too high rigidity). That is, since the width of a cutting chip becomes a width corresponding to the feed pitch of the cutting tool  441  per rotation of the rotating liner  11  (a dimension equal to or less than the dimension of the feed pitch), the generation of a cutting chip having a predetermined sectional shape (a sectional shape that prevents a too high rigidity) is enabled by properly setting the feed pitch. In this embodiment, the feed pitch is set to a constant value from the cutting start to the cutting end of the weld bead FB (a constant value in all the phases). For example, the feed pitch is set to 0.1 mm. The feed pitch is not limited to this value. Taking into account the hardness of the liner  11  and so on, the feed pitch is set to a value that causes a cutting chip to have a rigidity that enables the suction and recovery of the cutting chip without getting caught in the suction port  701  of the suction device  700 . 
     In  FIG. 10 , broken lines each indicate the cutting locus per rotation of the liner  11 . That is, the broken lines each indicate the relative moving locus (relative to the liner  11 ) of the cutting tool  441  per rotation in the region A portion in  FIG. 5 . Broken lines in  FIG. 6  also each indicate a cutting region by the cutting tool  441  per rotation in the region A portion. In the actual cutting process, the cutting tool  441  is moved by the feed pitch per rotation from the moving locus of the broken line on the right side in the figure to the moving locus of the broken line on the left side in sequence. These figures illustrate a case where the cutting tool  441  completes the cutting of the weld bead FB by about eight rotations (eight times of rotation) of the liner  11 . However, actually, this number of times of rotation is determined according to the setting of the feed pitch. The machining information creation part  560  creates as the position information the positions of the cutting tool  441  per rotation for the respective phases (the respective phases α 1 , α 2 , α 3 , α 4 , α 5  in  FIG. 10 ) so that the cutting tool  441  moves along the moving loci described above. That is, intersection points between straight lines indicating the phases α 1 , α 2 , α 3 , α 4 , α 5  and the broken lines each indicating the moving locus of the cutting tool  441  per rotation in  FIG. 10  are created as the position information. The moving locus of the cutting tool  441  in the final rotation of the liner  11  is set so that the sectional area (particularly the width) of a cutting chip generated by the cutting tool  441  moved along this moving locus becomes equal to or less than the feed pitch. In  FIG. 10 , a dimension P is the feed pitch per rotation of the liner  11  (this also applies to  FIGS. 11 and 12 ). 
     Likewise, broken lines in  FIG. 11  each indicate the cutting locus per rotation of the liner  11  in the region B portion in  FIG. 5 . That is, the broken lines each indicate the relative moving locus of the cutting tool  441  per rotation in the region B portion in  FIG. 5 . Broken lines in  FIG. 7  also each indicate a cutting region by the cutting tool  441  per rotation in the region B portion. 
     Likewise, broken lines in  FIG. 12  each indicate the cutting locus per rotation of the liner  11  in the region C portion in  FIG. 5 . That is, the broken lines each indicate the relative moving locus of the cutting tool  441  per rotation in the region C portion in  FIG. 5 . Broken lines in  FIG. 8  also each indicate a cutting region by the cutting tool  441  per rotation in the region C portion. 
     As seen from these figures, the relative moving locus of the cutting tool  441  per rotation of the liner  11  is created as information such that it is the cutting locus that approximately coincides with the shape of the end edge of the weld bead FB on the right side, and is moved in the feed direction at the constant feed pitch P. 
     Then, the information for moving the cutting tool  441  along such moving loci is transmitted to the cutting tool feed control part  520  at the time of the cutting machining of the weld bead FB, and is used as information for the cutting tool feed control part  520  to control the sliding movement position of the second slider  430 . 
     Weld Bead Cutting Operation 
     Next, the cutting operation of the weld bead FB performed by the weld bead cutting device  100  will be described. 
     As illustrated in  FIG. 9  (a diagram illustrating the sequence of the weld bead cutting process), processes of “bead end edge position measurement”, “bead width calculation”, “bead profile information creation”, “machining information creation”, and “bead cutting machining” are performed in this order in the cutting operation of the weld bead FB. A specific description will be given below. 
     As illustrated in  FIGS. 2 and 3 , the cutting operation of the weld bead FB is performed in the state where the liner  11  is set in the weld bead cutting device  100 . That is, the cutting operation of the weld bead FB is performed in the state where the workpiece (the intermediate molded product of the tank  1  at the stage before the reinforcing portion  12  is formed) is set in the weld bead cutting device  100 . The workpiece is in a state in which the caps  3 A,  3 B are attached to the liner  11  formed by joining (welding) the center liner portion  21  and the side liner portions  22 ,  23  to each other in the separate process (the production process of the liner  11 ). 
     When setting the liner (the workpiece)  11  in the weld bead cutting device  100 , first, the unit bodies  301  of the liner rotation units  300  are moved in the horizontal direction (the X-direction) on the rail (not illustrated) provided on the base plate  201  so that the unit bodies  301  are spaced apart from each other by a predetermined distance (a distance longer than the length of the liner  11  in the direction along the axial direction). Then, in the state where the liner  11  is temporarily held above the base plate  201 , the liner rotation units  300  are advanced toward each other, and the fitting portions  303  respectively provided at the distal end portions of the rotation rods  302  are respectively inserted and fitted into the openings  31   a,    31   b  provided in the caps  3 A,  3 B, respectively. Further, the caps  3 A,  3 B are retained by the retaining members  304  respectively attached to the distal end portions of the rotation rods  302  so that the rotation of the caps  3 A,  3 B relative to the rotation rods  302  is disabled, respectively. Consequently, when the rotation rods  302  are rotated, the rotational forces are transmitted to the liner  11  to enable the rotation of the liner  11  about the horizontal axis (about the horizontal axis in the X-direction). 
     In the state where the liner  11  is set in the weld bead cutting device  100  as described above, as illustrated in  FIG. 4 , the cutting unit  400  is at a retreat position (a retreat position with a predetermined distance from the liner  11 ), and the cutting tool  441  is at a position with a predetermined distance from the liner  11 . 
     After the liner  11  is set in the weld bead cutting device  100  as described above, the electric motors of the liner rotation units  300  are operated, and the cutting operation of the weld bead FB is performed in the state where the liner  11  is rotated about the horizontal axis (about the horizontal axis in the X-direction). 
     In the cutting operation of the weld bead FB, first, the bead end edge position measurement is performed. In the bead end edge position measurement, in the state where the liner  11  is rotated about the horizontal axis, laser light is sequentially irradiated from the light emitter of the distance sensor  600  over the entire circumference (over the phases in the rotation direction) of the weld bead FB and its peripheral portion in its circumferential direction (the circumferential direction of the liner  11 ), and the time from the irradiation of the laser light until the laser light is reflected by the surface of the liner  11  or the weld bead FB and received by the light receiver is measured, thereby measuring the shape of the surrounding of the weld bead FB. Then, information on the positions of the first end edge and the second end edge of the weld bead FB in its width direction per phase in the circumferential direction of the liner  11  is transmitted from the distance sensor  600  to the bead end edge position information acquisition part  530 . By receiving an output signal from the distance sensor  600 , the bead end edge position information acquisition part  530  acquires the information on the positions of the first end edge and the second end edge of the weld bead FB in its width direction per phase. That is, information on the distance from one of the end edges of the liner  11  in its longitudinal direction to the first end edge of the weld bead FB in its width direction, and information on the distance from the one of the end edges of the liner  11  in its longitudinal direction to the second end edge of the weld bead FB in its width direction are acquired per phase at every predetermined angle (e.g. every 1°) in the circumferential direction of the liner  11 . 
     In the bead width calculation process, the bead width calculation part  540  calculates the dimension of the weld bead FB in its width direction per phase at every predetermined angle (e.g. every 1°) in the circumferential direction of the liner  11 . That is, this calculation is performed by subtracting the distance between the reference point and the first end edge of the weld bead FB in its width direction from the distance between the reference point and the second end edge of the weld bead FB in its width direction per phase. 
     In the bead profile information creation process (a bead profile information creation step referred to in the disclosure), the bead profile information creation part  550  obtains the shapes of both side edges (both side edges extending in the circumferential direction of the liner  11 ) of the weld bead FB by connecting, in the circumferential direction of the liner  11 , the positions (the positions in the respective phases) of both end edges of the weld bead FB in its width direction acquired by the bead end edge position information acquisition part  530 . 
     In the machining information creation process (a machining information creation step referred to in the disclosure), according to the bead profile information on the end edges of the weld bead FB created by the bead profile information creation part  550 , the machining information creation part  560  creates position information of the cutting tool  441  in its feed direction (the direction along the width direction of the weld bead FB) for use when cutting the weld bead FB by the cutting tool  441 . That is, using the bead profile information on one of the sides (e.g. on the right side) out of the bead profile information on both end edges of the weld bead FB, information defining the position of the cutting tool  441  in its feed direction per phase is created so as to obtain a cutting locus that approximately coincides with the shape of the end edge of the weld bead FB along the circumferential direction of the liner  11  being this bead profile information. Further, information defining the position of the cutting tool  441  in its feed direction (the position of the cutting tool  441  in its feed direction per rotation of the liner  11 ) per phase is created so that even in the state where the cutting tool  441  is moved in the width direction by a predetermined feed pitch per rotation of the rotating liner  11 , the cutting locus (the cutting locus that approximately coincides with the shape of the end edge of the weld bead FB along the circumferential direction of the liner  11 ) is obtained. 
     In the bead cutting machining, the cutting operation of the weld bead FB is actually performed. First, the first slider  420  is caused to slide in the direction (the Y-direction) toward the liner  11  by the control by the cutting unit advance and retreat control part  510 . Consequently, the sliders  420 ,  430  slide integrally in the direction toward the liner  11 . In this event, the position of the cutting tool  441  in the bead width direction is a position where the cutting tool  441  is not in contact with the weld bead FB. 
     By the sliding movement of the first slider  420  by the control by the cutting unit advance and retreat control part  510 , the cutting tool  441  slides in the Y-direction (slides in the direction toward the weld bead FB). For example, the tip of the cutting tool  441  is maintained at a position retreated from the outer peripheral surface of the liner  11  by about 2 mm. 
     In this state, the cutting tool feed control part  520  receives the machining information created by the machining information creation part  560 , and the cutting tool feed control part  520  moves the cutting tool  441  along the moving loci according to the machining information. That is, as indicated by the broken lines in  FIGS. 10, 11, and 12 , the position of the cutting tool  441  in its feed direction is controlled per rotation of the liner  11  along the cutting locus that approximately coincides with the shape of the end edge of the weld bead FB along the circumferential direction of the liner  11  so that the control of the position of the cutting tool  441  in its feed direction along the cutting locus is performed per rotation. That is, by causing the second slider  430  to slide in the X-direction (to slide at a predetermined feed pitch per rotation), the weld bead FB is cut while generating a cutting chip with an approximately constant width (while being cut in a manner of so-called katsuramuki (rotary peeling)) (a cutting tool feed control step referred to in the disclosure). 
     In this embodiment, the weld bead FB is almost removed, for example, by performing twice the cutting process (the cutting process achieved by moving the cutting tool  441  in the X-direction) of the weld bead FB. That is, in the first cutting process, as described above, the cutting is performed by moving the cutting tool  441  in the X-direction in the state where the tip of the cutting tool  441  is maintained at the position retreated from the outer peripheral surface of the liner  11  by about 2 mm. Then, in the second cutting process, the cutting is performed by moving the cutting tool  441  in the X-direction in the state where the tip of the cutting tool  441  is maintained at a position almost in contact with the outer peripheral surface of the liner  11 . The cutting loci of the cutting tool  441  in the second cutting process are the same as the cutting loci of the cutting tool  441  in the first cutting process (see the broken lines in  FIGS. 10, 11, and 12 ). The weld bead FB is almost removed by performing the first and second cutting processes. Also in the second cutting process, the respective processes (see  FIG. 9 ) may be performed in order from the bead end edge position measurement process like in the first cutting process described above. 
     It may be configured that the weld bead FB is almost removed by performing the cutting process once, or by performing the cutting process three times or more. That is, this embodiment is the case where the weld bead FB is almost removed without the need for cutting of the weld bead FB by the advance and retreat movements (the movements in the Y-direction) of the cutting tool  441  (cutting for eliminating the level difference of the liner outer peripheral surface, due to the weld bead FB, by the movements of the cutting tool  441  in the Y-direction) which will be described in a later-described third embodiment. In particular, the cutting process in this embodiment can be realized in the case where the section (the section in the direction perpendicular to the central axis) of the liner  11  is almost a perfect circle. 
     Effects of the Embodiment 
     As described above, in this embodiment, the machining information of the liner  11  per rotation of the liner  11  being the position information of the cutting tool  441  in the bead width direction per phase in the circumferential direction of the liner  11  is created based on the created bead profile information so that the moving locus of the cutting tool  441  relative to the liner  11  approximates the shape of the end edge of the weld bead FB per rotation of the liner  11 . According to this machining information, the position of the cutting tool  441  in the bead width direction per rotation of the liner  11  is controlled. Therefore, the shape of a cutting chip generated by the cutting can be adjusted as desired (the shape of a cutting chip can be adjusted to be equal to or less than the feed pitch according to the setting of the feed pitch) so that it is possible to generate a cutting chip having a predetermined sectional shape (a sectional shape that prevents a too high rigidity). As a result, it is possible to generate a cutting chip that can be easily sucked and recovered by the suction device  700 . 
     Second Embodiment 
     Next, a second embodiment will be described. In the first embodiment described above, the feed pitch (the dimension P in  FIGS. 10 to 12 ) of the cutting tool  441  per rotation of the rotating liner  11  is constant. In this embodiment, the feed pitch of the cutting tool  441  per rotation of the rotating liner  11  is changed per phase according to the dimension of the weld bead FB in its width direction. Specifically, as the dimension of the weld bead FB in its width direction becomes smaller (for the phase with a smaller dimension of the weld bead FB in its width direction), the feed pitch of the cutting tool  441  per rotation of the liner  11  is set to be smaller. In other words, as the dimension of the weld bead FB in its width direction becomes greater, the feed pitch of the cutting tool  441  per rotation of the liner  11  is set to be greater. More specifically, the feed pitch of the cutting tool  441  is changed per phase so that the moving locus (the cutting locus) of the cutting tool  441  does not deviate from the weld bead FB, i.e. the cutting tool  441  continues to be in contact with the weld bead FB (continues to cut the weld bead FB) from the start to the end of the cutting machining. 
     Therefore, in this embodiment, based on information on the positions of both end edges of the weld bead FB in the bead width direction over the entire circumference of the liner  11  in its circumferential direction measured by the distance sensor  600 , the bead profile information creation part  550  creates bead profile information as information on the shapes of both end edges of the weld bead FB over the entire circumference of the liner  11  in its circumferential direction. 
     Further, the machining information creation part  560  creates machining information in which the feed pitch of the cutting tool  441  per phase in the circumferential direction of the liner  11  is changed so that the position of the cutting tool  441  in the bead width direction per phase in the circumferential direction of the liner  11  from the cutting start position to the cutting end position in the bead width direction is located closer to the center side of the weld bead FB than the positions of both end edges of the weld bead FB per rotation of the liner  11 . 
     This information creation operation corresponds to an operation of “creating machining information in which the feed pitch of the cutting tool per phase in the circumferential direction of the workpiece is changed so that the position of the cutting tool in the bead width direction per phase in the circumferential direction of the workpiece from a cutting start position to a cutting end position in the bead width direction is located closer to a center side of the weld bead than the positions of both end edges of the weld bead per rotation of the workpiece” referred to in the disclosure. 
       FIG. 13  illustrates the region A portion in  FIG. 5 , and broken lines in  FIG. 13  indicate moving loci of the cutting tool  441  in this embodiment. Likewise,  FIG. 14  illustrates the region B portion in  FIG. 5 , and broken lines in  FIG. 14  also indicate moving loci of the cutting tool  441  in this embodiment. Likewise,  FIG. 15  illustrates the region C portion in  FIG. 5 , and broken lines in  FIG. 15  also indicate moving loci of the cutting tool  441  in this embodiment. 
     In this embodiment, in order to obtain such moving loci, using the bead profile information on both end edges of the weld bead FB, the machining information creation part  560  creates information defining the position of the cutting tool  441  in its feed direction per phase so as to obtain a cutting locus that approximately coincides with the shape of the end edge (the end edge on the right side) of the weld bead FB along the circumferential direction of the liner  11  being the bead profile information. Further, the machining information creation part  560  creates information defining the position of the cutting tool  441  in its feed direction, that adjusts the feed pitch per phase so that the moving locus of the cutting tool  441  in the final rotation of the liner  11  does not straddle the end edge (the end edge on the left side) of the weld bead FB along the circumferential direction of the liner  11  being the bead profile information. 
     Therefore, as illustrated in  FIGS. 13 to 15 , in the region where the dimension of the weld bead FB in its width direction is relatively large (e.g. the region A portion in  FIG. 5 ), the feed pitch of the cutting tool  441  is also set to be relatively large (see a feed pitch P 1  in  FIG. 13 ). For the feed pitch in this case, an upper limit (e.g. 0.2 mm) is set in advance as a range in which the rigidity of a cutting chip does not become too high. On the other hand, in the region where the dimension of the weld bead FB in its width direction is relatively small (e.g. the region C portion in  FIG. 5 ), the feed pitch of the cutting tool  441  is also set to be relatively small (see a feed pitch P 2  in  FIG. 15 ). 
     By changing the feed pitch of the cutting tool  441  according to the dimension of the weld bead FB in its width direction per phase in this way, the moving locus of the cutting tool  441  does not deviate from the weld bead FB so that a cutting chip generated by cutting per phase becomes continuous without being broken off from the start to the end of the cutting machining. That is, the cutting chip is removed from the liner  11  as a single cutting chip. Therefore, when the suction and recovery of a cutting chip, generated at the start of the cutting machining, into the suction port  701  of the suction device  700  is started, a cutting chip generated (continuously generated) thereafter is pulled into the suction port  701  by the cutting chip sucked and recovered earlier. Consequently, all the cutting chip (the single continuous cutting chip) is sucked and recovered into the suction port  701  of the suction device  700  well. Then, at the end of the final rotation, all the weld bead FB is removed from the liner  11 . 
     Since the other configuration and cutting operation are the same as in the case of the first embodiment described above, a description thereof is omitted herein. 
     According to this embodiment, even when the sectional area of a cutting chip becomes extremely large or extremely small, since the cutting chip becomes continuous without being broken off from the start to the end of the cutting machining, the cutting chip is sucked and recovered into the suction port  701  of the suction device  700  well. 
     That is, even in the situation where a cutting chip with a large sectional area and thus with a high rigidity is generated (e.g. see a cutting chip FB 1  in  FIG. 13  and a cutting chip FB 2  in  FIG. 15 ), the cutting chip can be sucked and recovered into the suction port  701  of the suction device  700  well. 
     When a cutting chip with an extremely small sectional area is broken off, curling occurs in a cutting chip at this portion. In this case, there is a possibility that the generation direction of the cutting chip (the direction in which the cutting chip extends due to the curling) may become different from the direction toward the suction port  701  of the suction device  700  to impede the suction and recovery by the suction device  700 . Further, since the cutting chip is slightly electrified, if the cutting chip with the extremely small sectional area is broken off, there is also a possibility that the electrified cutting chip may be adhered (electrically adhered) to the liner  11 , and also in this case, there is a possibility of impeding the suction and recovery by the suction device  700 . According to this embodiment, since the cutting chip becomes continuous without being broken off from the start to the end of the cutting machining as described above, even when the sectional area of the cutting chip becomes extremely small, the cutting chip can be sucked and recovered into the suction port  701  of the suction device  700  well. 
     In this embodiment, in order to avoid that the sectional area of the cutting chip becomes extremely large or extremely small, the number of rotations (the number of times of rotation) of the liner  11  from the cutting start to the cutting end of the weld bead FB may be set to be variable. That is, when it is conjectured that the sectional area of the cutting chip becomes extremely large, the number of rotations of the liner  11  from the cutting start to the cutting end of the weld bead FB is increased. That is, the feed pitch is changed to be smaller. Conversely, when it is conjectured that the sectional area of the cutting chip becomes extremely small, the number of rotations of the liner  11  from the cutting start to the cutting end of the weld bead FB is reduced. That is, the feed pitch is changed to be greater. 
     Third Embodiment 
     Next, a third embodiment will be described. In the first and second embodiments described above, the description has been given only of the case where the weld bead FB is cut while moving (feeding) the cutting tool  441  along the width direction of the weld bead FB. In this embodiment, in addition to this cutting, there is provided a process of cutting the weld bead FB by moving the cutting tool  441  along the height direction of the weld bead FB (the radial direction of the liner  11 ; the Y-direction). That is, after the cutting machining in which the weld bead FB is cut while moving the cutting tool  441  along the width direction of the weld bead FB (hereinafter referred to as the rough machining) is performed, the cutting machining in which the weld bead FB remaining after the rough machining is cut by moving the cutting tool  441  along the height direction of the weld bead FB to remove the remaining weld bead FB almost completely so that the outer peripheral surface of the liner  11  has a smooth curved surface by preventing the weld bead FB from remaining on the outer peripheral surface of the liner  11  (hereinafter referred to as the finish machining) is performed. 
       FIG. 16  is a sectional view of the weld bead FB and its peripheral portion after the cutting machining (the rough machining) according to the first embodiment or the second embodiment described above is performed. In  FIG. 16 , broken lines each indicate a cutting region by the cutting tool  441  per rotation in the rough machining. As illustrated in  FIG. 16 , the weld bead FB slightly remains after the rough machining, and the remaining weld bead FB is cut by the finish machining. 
     In general, when the section (the section in the direction perpendicular to the central axis) of the liner is a perfect circle and the center position of the section coincides with the rotation centers of the rotation rods  302 , the distance between the rotation center of the liner and the outer peripheral surface of the liner is uniform over the entire circumference of the liner. Therefore, it is possible to cut the weld bead FB well over its entirety in the circumferential direction by simply rotating the liner  11  while the cutting tool  441  is fixed at a position in contact with the root of the weld bead FB (a position where the entire weld bead FB can be cut). 
     However, there are cases where the section of the actual liner  11  is not a perfect circle (e.g. the section is an elliptical shape) due to the influence of a machining error or centrifugal force caused by rotation. Even when the section of the liner is a perfect circle, there are cases where the distance between the rotation center and the outer peripheral surface of the liner  11  becomes non-uniform over the entire circumference of the liner  11  due to the influence of the centrifugal force. 
     Therefore, in the situation where the cutting tool  441  faces a region where the distance between the rotation center and the outer peripheral surface of the liner  11  is short, there is a possibility that the cutting tool  441  may not reach the root of the weld bead FB. That is, there is a possibility that the weld bead FB may be partially left uncut. On the other hand, in the situation where the cutting tool  441  faces a region where the distance between the rotation center and the outer peripheral surface of the liner  11  is long, there is a possibility that the cutting tool  441  may reach not only the weld bead FB but also the outer peripheral surface of the liner  11  to cut the outer peripheral surface of the liner  11 . That is, there is a possibility that the liner  11  may be partially thinned or perforated. 
     In this embodiment, even when the section of the liner  11  is not a perfect circle, or the distance between the rotation center and the outer peripheral surface  11   a  of the liner  11  is non-uniform over the entire circumference of the liner  11  (the distance is non-uniform even when the section of the liner  11  is a perfect circle), it is possible to cut the weld bead FB well with high accuracy over its entirety in the circumferential direction by the finish machining. 
     In this embodiment, points that differ from the first embodiment described above will be described.  FIG. 17  is a plan view illustrating a state in which the liner  11  is set in the weld bead cutting device  100  according to this embodiment.  FIG. 18  is a diagram illustrating the cutting unit  400  and its control system in the weld bead cutting device  100  according to this embodiment.  FIG. 18  is a diagram as viewed from arrow B in  FIG. 17 . 
     As illustrated in  FIGS. 17 and 18 , the cutting unit  400  of the weld bead cutting device  100  according to this embodiment includes a third slider  440  in addition to the first slider  420  and the second slider  430 . The third slider  440  is supported by a rail  431  provided on the second slider  430  and extending along the Y-direction. The third slider  440  is slidable on the rail  431  along the Y-direction. A power source for sliding movement of the third slider  440  is an electric motor (not illustrated). Alternatively, the power source may be another power source. 
     The cutting tool  441  for cutting the weld bead FB is detachably attached to a distal end portion (a distal end portion on the liner  11  side) of the third slider  440 . 
     The first slider  420  includes roller units  422 ,  423 . The roller units  422 ,  423  are respectively disposed on both sides (both sides in the X-direction) of the cutting tool  441 . Herein, the roller unit  422  on the right side in  FIG. 17  will be referred to as the first roller unit  422 , and the roller unit  423  on the left side in  FIG. 17  will be referred to as the second roller unit  423 . The distance (the distance in the X-direction) between the cutting tool  441  and the first roller unit  422  and the distance (the distance in the X-direction) between the cutting tool  441  and the second roller unit  423  are equal to each other and are set to be relatively short. Specifically, these distances are set to be as short as possible within a range where the roller units  422 ,  423  do not interfere with the weld bead FB (later-described rollers  425   a,    425   b,    426   a,    426   b  do not interfere with the weld bead FB) when the cutting tool  441  cuts the weld bead FB. 
     As illustrated in  FIG. 18 , the first roller unit  422  is configured such that the upper and lower rollers  425   a,    425   b  in a pair are supported by a support arm  424  joined to a distal end surface (a distal end surface on the liner  11  side) of the first slider  420 . 
     The support arm  424  includes a first horizontal portion  424   a,  a first vertical portion  424   b,  a second horizontal portion  424   c,  a second vertical portion  424   d,  a third vertical portion  424   e,  a third horizontal portion  424   f,  and a fourth horizontal portion  424   g.  The first horizontal portion  424   a  extends in the horizontal direction from the distal end surface of the first slider  420  along the Y-direction. The first vertical portion  424   b  extends vertically upward from a distal end portion (a distal end portion on the liner  11  side) of the first horizontal portion  424   a.  The second horizontal portion  424   c  extends in the horizontal direction from an upper end of the first vertical portion  424   b  along the Y-direction. The second vertical portion  424   d  and the third vertical portion  424   e  respectively extend vertically upward and downward from a distal end portion of the second horizontal portion  424   c.  The third horizontal portion  424   f  extends in the horizontal direction from an upper end of the second vertical portion  424   d  along the Y-direction and supports the roller  425   a  so that the roller  425   a  is rotatable about the X-axis. The fourth horizontal portion  424   g  extends in the horizontal direction from a lower end of the third vertical portion  424   e  along the Y-direction and supports the roller  425   b  so that the roller  425   b  is rotatable about the X-axis. 
     The positions of the rollers  425   a,    425   b  in the Y-direction coincide with each other. That is, the distances from the distal end surface of the first slider  420  to the outer peripheral ends of the rollers  425   a,    425   b  on the liner  11  side (the outer peripheral surfaces of the rollers  425   a,    425   b  on the side facing the outer peripheral surface  11   a  of the liner  11 ) (a distance t in  FIG. 17 ) are equal to each other. 
     The height positions of the rollers  425   a,    425   b  are set so that the cutting tool  441  is located between the upper roller  425   a  and the lower roller  425   b  in a side view illustrated in  FIG. 18 . That is, the height position at which the cutting tool  441  is disposed is lower than the height position at which the upper roller  425   a  is disposed, and higher than the height position at which the lower roller  425   b  is disposed. 
     The second roller unit  423  has the configuration similar to the first roller unit  422  and is configured such that the upper and lower rollers  426   a,    426   b  in a pair are supported by a support arm  426 . The positions of the rollers  426   a,    426   b  in the Y-direction respectively coincide with the positions of the rollers  425   a,    425   b  in the Y-direction. That is, the distances from the distal end surface of the first slider  420  to the outer peripheral ends of the rollers  426   a,    426   b  on the liner  11  side (the distance t in  FIG. 17 ) are equal to each other. 
     The height positions of the rollers  426   a,    426   b  are also set so that the cutting tool  441  is located between the upper roller  426   a  and the lower roller  426   b  in a side view. That is, the height position at which the cutting tool  441  is disposed is lower than the height position at which the upper roller  426   a  is disposed, and higher than the height position at which the lower roller  426   b  is disposed. 
     In this way, the four rollers  425   a,    425   b,    426   a,    426   b  in total are respectively disposed on both sides of the cutting tool  441  in the X-direction and the Z-direction. Since the disposition positions of the rollers  425   a,    425   b,    426   a,    426   b  are set as described above, a virtual plane connecting the outer peripheral ends of the rollers  425   a,    425   b,    426   a,    426   b  on the liner  11  side to each other is a plane extending along the X-direction and the Z-direction (a plane extending along the vertical direction). The rollers  425   a,    425   b,    426   a,    426   b  are made of the same material and have the same diameter. The material may be resin or metal. 
     A distance sensor (a surface position measuring device)  450  for measuring the distance to the outer peripheral surface  11   a  of the liner  11  is provided at a boundary portion between the second vertical portion  424   d  and the third vertical portion  424   e  of the support arm  424  of the first roller unit  422 . The distance sensor  450  is formed by an ultrasonic sensor or an optical sensor and is a non-contact sensor that measures the distance to the outer peripheral surface  11   a  of the liner  11 . Since the configuration of this non-contact sensor is known, a description thereof is omitted herein. 
     Further, a distance sensor  450  having the same configuration as described above is also provided at a boundary portion between a second vertical portion (corresponding to the second vertical portion  424   d ) and a third vertical portion (corresponding to the third vertical portion  424   e ) of the support arm  424  of the second roller unit  423 . 
     The height positions at which the distance sensors  450  are disposed are set to coincide with each other. Further, the positions of the distance sensors  450  in the Y-direction are also set to coincide with each other. Therefore, when there is no deflection of the outer peripheral surface  11   a  of the liner  11  set in the weld bead cutting device  100  (when the outer peripheral surface  11   a  of the liner  11  is a cylindrical surface with no deflection), the distances to the outer peripheral surface  11   a  of the liner  11  detected by the distance sensors  450  become equal to each other. 
     In this embodiment, the distance sensor  450  is formed by the non-contact sensor, but it may be formed by a contact sensor. 
     The controller  500  in this embodiment includes, in addition to the respective functional parts in the first embodiment described above, a cutting tool advance and retreat control part  570 , a surface position data acquisition part  581 , a profile machining data creation part  582 , a profile machining data offset processing part  583 , and a measurement result determination part  584 . 
     When the third slider  440  is caused to slide by the control by the cutting tool advance and retreat control part  570 , only the third slider  440  slides in the Y-direction (slides relative to the first slider  420  and the second slider  430 ). This sliding movement causes the cutting tool  441  to slide in the Y-direction. 
     The surface position data acquisition part  581  acquires distance data measured by the distance sensors  450  (measurement data of the distances to the outer peripheral surface  11   a  of the liner  11 ) from the distance sensors  450 , respectively. 
     As described above, the distance sensors  450  are respectively provided at the boundary portions between the second vertical portion  424   d  and the third vertical portion  424   e  of the support arm  424  of the first roller unit  422  and between the second vertical portion and the third vertical portion of the support arm  426  of the second roller unit  423 . Therefore, as illustrated in  FIG. 19 , in the state where the rollers  425   a,    425   b,    426   a,    426   b  are pressed against the outer peripheral surface  11   a  on both sides (both sides in the X-direction) of the weld bead FB, respectively, the distance sensors  450  also face the outer peripheral surface  11   a  on both sides (both sides in the X-direction) of the weld bead FB, respectively. Broken lines in  FIG. 19  respectively indicate regions to be targets for the distance sensors  450  to measure the distances, respectively. 
     Then, the distances to the outer peripheral surface  11   a  of the liner  11  on both sides (both sides in the direction along the butting direction) of the weld bead FB are respectively measured by the distance sensors  450 , and the surface position data acquisition part  581  acquires the measurement data (the distance data). That is, the distance sensor  450  provided to the first roller unit  422  measures the distance to a position, in close vicinity to the weld bead FB, of the outer peripheral surface of the center liner portion  21 . Likewise, the distance sensor  450  provided to the second roller unit  423  measures the distance to a position, in close vicinity to the weld bead FB, of the outer peripheral surface of the side liner portion  22 . Then, in this state, the rotation rods  302  of the liner rotation units  300  are rotated to rotate the liner  11  about the horizontal axis (about the horizontal axis in the X-direction), and the distance sensors  450  respectively measure the distances over the entire circumference (per phase in the circumferential direction) with respect to a position, in close vicinity to the weld bead FB, of the outer peripheral surface of the center liner portion  21  and a position, in close vicinity to the weld bead FB, of the outer peripheral surface of the side liner portion  22  (measure the distances over the entire circumference with respect to positions on one-dot chain lines in  FIG. 19 ). Then, the surface position data acquisition part  581  acquires these measurement data. 
     Based on the distance data (the measurement data) acquired from the distance sensors  450  by the surface position data acquisition part  581 , the profile machining data creation part  582  extracts, out of both distance data to the positions of the outer peripheral surfaces in the same phase in the circumferential direction (located at positions adjacent to each other in the X-direction), the distance data on the side where the distance to the outer peripheral surface  11   a  of the liner  11  is shorter. That is, based on the distance data acquired from the distance sensors  450 , the profile machining data creation part  582  compares information on the positions of the outer peripheral surfaces in the same phase in the circumferential direction and extracts the information on the position of the outer peripheral surface  11   a  located on the outer peripheral side (the side closer to the distance sensor  450 ). 
     Specifically, as described above, the distance sensor  450  provided to the first roller unit  422  measures the distance to a position, in close vicinity to the weld bead FB, of the outer peripheral surface of the center liner portion  21 , and the distance sensor  450  provided to the second roller unit  423  measures the distance to a position, in close vicinity to the weld bead FB, of the outer peripheral surface of the side liner portion  22 . In this case, out of the positions of the outer peripheral surfaces in the same phase in the circumferential direction (the position of the outer peripheral surface of the center liner portion  21  measured by the distance sensor  450  of the first roller unit  422 , and the position of the outer peripheral surface of the side liner portion  22  measured by the distance sensor  450  of the second roller unit  423 ), the profile machining data creation part  582  extracts only the information measured by the distance sensor  450  of the first roller unit  422  when the distance to the outer peripheral surface of the center liner portion  21  measured by the distance sensor  450  of the first roller unit  422  is shorter. Conversely, the profile machining data creation part  582  extracts only the information measured by the distance sensor  450  of the second roller unit  423  when the distance to the outer peripheral surface of the side liner portion  22  measured by the distance sensor  450  of the second roller unit  423  is shorter. The information extraction operation described above is performed per predetermined phase over the entire circumference of the outer peripheral surface  11   a  of the liner  11 . 
     The profile machining data offset processing part  583  calculates a distance (an offset amount) as distance data after the offset processing by subtracting a predetermined distance from the distance data per predetermined phase created by the profile machining data creation part  582 . This is the processing for preventing excessive cutting of the outer peripheral surface  11   a  of the liner  11 , taking into account a variation in the accuracy of the weld bead cutting device  100  (the positional accuracy of the tip of a cutting blade of the cutting tool  441 ). That is, the profile machining data is offset by a predetermined dimension so that a position located slightly closer to the cutting unit  400  (outwardly from the outer peripheral surface  11   a  of the liner  11 ) than a cutting position (a position of the tip of the cutting blade of the cutting tool  441 ) according to the distance data per predetermined phase created by the profile machining data creation part  582  is set as a position of the tip of the cutting blade of the cutting tool  441  The data subjected to the offset processing corresponds to “machining data obtained by correcting the profile machining data” referred to in the disclosure. 
     Then, in the cutting process of the weld bead FB, the machining data created as described above is transmitted to the cutting tool advance and retreat control part  570 , and the weld bead FB is cut while adjusting the advance-retreat position of the cutting tool  441  relative to the outer peripheral surface  11   a  of the liner  11  so that the distance between the position of the outer peripheral surface  11   a  per phase in the circumferential direction of the liner  11  in the machining data and the position of the tip of the cutting blade of the cutting tool  441  is maintained constant. 
     The measurement result determination part  584  is a processing part that determines, after the completion of the cutting process of the weld bead FB, whether or not the cutting operation of the weld bead FB has been properly performed. This determination is a process of inspecting the presence or absence of the unevenness of the outer peripheral surface of the liner  11  in a non-contact or contact manner. 
     Weld Bead Cutting Operation 
     Next, the cutting operation of the weld bead FB performed by the weld bead cutting device  100  according to this embodiment will be described. As described above, in this embodiment, after the cutting machining in which the weld bead FB is cut while moving the cutting tool  441  along the width direction of the weld bead FB (the rough machining) is performed, the cutting machining in which the weld bead FB is cut by moving the cutting tool  441  along the height direction of the weld bead FB to remove the weld bead FB almost completely so that the outer peripheral surface of the liner  11  has a smooth curved surface by preventing the weld bead FB from remaining on the outer peripheral surface of the liner  11  (the finish machining) is performed. Since the rough machining is the same as the first embodiment or the second embodiment described above, a description thereof is omitted herein. Accordingly, only the finish machining will be described below. 
     As illustrated in  FIG. 20  (a diagram illustrating the sequence of the finish machining), processes of “roller pressing”, “surface position measurement”, “profile machining data creation”, “profile machining data offset processing”, “digital profile machining”, “machining level difference measurement”, and “measurement result determination” are performed in this order in the finish machining. A specific description will be given below. 
     In the finish machining, first, before operating the electric motors (before rotating the liner  11 ), the first slider  420  is caused to slide in the direction (the Y-direction) toward the liner  11  by the control by the cutting unit advance and retreat control part  510 . Consequently, the sliders  420 ,  430 ,  440  slide integrally in the direction toward the liner  11 . By this sliding movement, as illustrated in  FIG. 21 , the rollers  425   a,    425   b,    426   a,    426   b  come in contact with the outer peripheral surface  11   a  of the liner  11  (roller pressing). 
     Then, the cutting unit advance and retreat control part  510  causes the first slider  420  to slide so that the distance (the distance in the Y-direction) between the rotation center (the central axis) O of the liner  11  (that coincides with the rotation centers of the rotation rods  302 ) and each of the rollers  425   a,    425   b,    426   a,    426   b  becomes a predetermined distance (a distance L in  FIG. 21 ). The distance L is determined in advance by experiments or simulations as a value that causes a region of the outer peripheral surface  11   a  of the liner  11  surrounded by the rollers  425   a,    425   b,    426   a,    426   b  (a generally rectangular region with vertices at positions where the outer peripheral surfaces of the rollers  425   a,    425   b,    426   a,    426   b  press the outer peripheral surface  11   a  of the liner  11 , respectively) to become a flat surface (a value that enables the region to be compulsorily deformed to a flat surface) when the outer peripheral surface  11   a  of the liner  11  is pressed by the rollers  425   a,    425   b,    426   a,    426   b.  At this time point, the cutting tool  441  is at a position retreated from the outer peripheral surface  11   a  of the liner  11  by a predetermined distance. In this way, in the state where the outer peripheral surface  11   a  of the liner  11  is pressed by the rollers  425   a,    425   b,    426   a,    426   b,  there is almost no unevenness on the outer peripheral surface  11   a  of the liner  11  surrounded by the rollers  425   a,    425   b,    426   a,    426   b  (the outer peripheral surface  11   a  becomes a flat surface as described above). That is, only the weld bead FB projects on the outer peripheral surface  11   a  with no unevenness. 
     In this state, a shift is made to the surface position measurement process. As described above, the surface position measurement is performed such that the distances to the outer peripheral surface  11   a  of the liner  11  on both sides (both sides in the direction along the butting direction) of the weld bead FB are respectively measured by the distance sensors  450 , and that the surface position data acquisition part  581  acquires the measurement data (the distance data). That is, while rotating the liner  11  about the horizontal axis in the state of  FIG. 21 , the distances to the outer peripheral surfaces of the liner  11  are measured by the distance sensors  450 , and the measurement data over the entire circumference of the liner  11  (the measurement data over the entire circumference with respect to the positions on the one-dot chain lines in  FIG. 19 ) is transmitted to the surface position data acquisition part  581 . 
     The profile machining data creation process thereafter is the process performed by the profile machining data creation part  582 , and as described above, based on the distance data acquired from the distance sensors  450  by the surface position data acquisition part  581 , the profile machining data creation part  582  extracts, out of both distance data to the positions of the outer peripheral surfaces in the same phase in the circumferential direction (located at the positions adjacent to each other in the X-direction), the distance data on the side where the distance to the outer peripheral surface  11   a  of the liner  11  is shorter. That is, based on the distance data acquired from the distance sensors  450 , the profile machining data creation part  582  compares information on the positions of the outer peripheral surfaces in the same phase in the circumferential direction and extracts the information on the position of the outer peripheral surface  11   a  located on the outer peripheral side (the side closer to the distance sensor  450 ). 
     The profile machining data offset processing is the process performed by the profile machining data offset processing part  583 , and as described above, the profile machining data offset processing part  583  calculates a distance as distance data after the offset processing by subtracting a predetermined distance from the distance data per predetermined phase created by the profile machining data creation part  582 . 
     After the profile machining data creation and the profile machining data offset processing are performed in this way, the digital profile machining is performed. In the digital profile machining, while rotating the liner  11 , the cutting tool  441  is advanced and retreated in the Y-direction according to the distance data obtained by the profile machining data offset processing. That is, the cutting tool advance and retreat control part  570  performs the control according to this distance data to cause the third slider  440  to slide so that the advance-retreat position of the cutting tool  441  is adjusted. That is, the weld bead FB is cut while adjusting the advance-retreat position of the cutting tool  441  relative to the outer peripheral surface  11   a  of the liner  11  so that the distance between the position of the outer peripheral surface  11   a  per phase in the circumferential direction of the liner  11  in the machining data (the distance data after the offset processing) and the position of the tip of the cutting blade of the cutting tool  441  is maintained constant. 
     The rotation speed of the liner  11  in the digital profile machining is equal to the rotation speed of the liner  11  in the surface position measurement process. Since the centrifugal force that acts on the liner  11  varies according to the rotation speed, this is for making centrifugal forces equal to each other in the digital profile machining and the surface position measurement process so that the displacement amounts of the outer peripheral surface  11   a  of the liner  11  due to the influence of the centrifugal force are made equal to each other. 
     Therefore, when the outer peripheral surface  11   a  of the liner  11  is spaced away from the cutting tool  441  (when there is deflection of the outer peripheral surface  11   a  of the liner  11  in the direction away from the cutting tool  441 ), the cutting tool  441  is advanced (the third slider  440  slides in the direction toward the liner  11 ). Conversely, when the outer peripheral surface  11   a  of the liner  11  approaches the cutting tool  441  (when there is deflection of the outer peripheral surface  11   a  of the liner  11  in the direction toward the cutting tool  441 ), the cutting tool  441  is retreated (the third slider  440  slides in the direction away from the liner  11 ). 
       FIG. 22  is a diagram corresponding to  FIG. 21  and illustrates a state in which the liner  11  is rotated by 90 degrees after the start of the digital profile machining. 
     In this way, since the weld bead FB is cut while adjusting the advance-retreat position of the cutting tool  441  relative to the outer peripheral surface  11   a  of the liner  11  so that the distance between the position of the outer peripheral surface  11   a  per phase in the circumferential direction of the liner  11  and the position of the tip of the cutting blade of the cutting tool  441  is maintained constant, as illustrated in  FIG. 23  (a diagram illustrating the relationship between the outer peripheral surface position of the liner  11  and the tip position of the cutting blade of the cutting tool  441  after the profile machining data is subjected to the offset processing), the weld bead FB is cut while the cutting tool  441  follows the outer peripheral surface  11   a  of the liner  11 . In  FIG. 23 , a solid line indicates a variation in the position (a state of deflection) of the outer peripheral surface  11   a  of the liner  11 , and a broken line indicates the tip positions of the cutting blade of the cutting tool  441 . A one-dot chain line in  FIG. 23  indicates the tip positions of the cutting blade of the cutting tool  441  in the rough machining. 
       FIG. 24  is a diagram corresponding to  FIG. 21  and illustrates a state in which the digital profile machining is completed. Although not illustrated in  FIG. 24 , the weld bead FB slightly remains at a dimension of the offset amount defined in the profile machining data offset processing described above. If the advance-retreat position of the cutting tool  441  is adjusted so that the tip position of the cutting blade of the cutting tool  441  is aligned with the proximal end position of the weld bead FB, it is possible to remove the weld bead FB almost completely. That is, the level difference due to the weld bead FB does not occur. 
     The machining level difference measurement is an operation of measuring the level difference of the outer peripheral surface  11   a  due to the weld bead FB being partially left uncut, and inspects the presence or absence of the unevenness of the outer peripheral surface  11   a  of the liner  11  in a non-contact or contact manner. The measurement result determination determines whether or not the level difference measured by the machining level difference measurement is equal to or less than a predetermined allowable level difference. When the level difference is equal to or less than the predetermined allowable level difference, it is determined to be normal. When the level difference exceeds the predetermined allowable level difference, it is determined to be abnormal. This information is displayed on a monitor or the like (not illustrated) installed in the weld bead cutting device  100 . 
     By the finish machining of this embodiment, even when the sections of the center liner portion  21  and the side liner portion  22  are not a perfect circle, or the distance between the rotation center O and the outer peripheral surface  11   a  of the liner  11  is non-uniform over the entire circumference of the liner  11  (the distance is non-uniform even when the section of the liner  11  is a perfect circle), it is possible to cut the weld bead FB well with high accuracy over its entirety in the circumferential direction. 
     Other Embodiments 
     The disclosure is not limited to the above-described embodiments, and all modifications and applications are made possible within the scope of the claims and its equivalent scope. 
     For example, in the third embodiment, in the finish machining in which the weld bead FB is cut by moving the cutting tool  441  along the height direction of the weld bead FB (the radial direction of the liner  11 ), the outer peripheral surface  11   a  of the liner  11  is compulsorily deformed to a flat surface by the pressing of the rollers  425   a,    425   b,    426   a,    426   b.  The disclosure is not limited thereto. Without compulsorily deforming the outer peripheral surface  11   a  of the liner  11  to a flat surface, the finish machining may be performed by moving the cutting tool  441  along the height direction of the weld bead FB. In this case, since not only both end positions of the weld bead FB in its width direction, but also the distance to the outer peripheral surface  11   a  of the liner  11  can be measured by the distance sensor  600 , it is possible to make the distance sensors  450  unnecessary. In this case, with respect to the timings of the measurement of both end positions of the weld bead FB in its width direction and the measurement of the distance to the outer peripheral surface  11   a  of the liner  11  by the distance sensor  600 , the measurement of both end positions of the weld bead FB in its width direction may be performed before the rough machining, and the measurement of the distance to the outer peripheral surface  11   a  of the liner  11  may be performed before the finish machining, or alternatively, the measurement of both end positions of the weld bead FB in its width direction and the measurement of the distance to the outer peripheral surface  11   a  of the liner  11  may be performed simultaneously. 
     In each of the above-described embodiments, the cutting tool  441  is the bit. The disclosure is not limited thereto. An end mill or a router may be employed as the cutting tool  441 . 
     In the third embodiment, the cutting unit  400  includes the four rollers  425   a,    425   b,    426   a,    426   b.  The disclosure is not limited thereto. One roller may be disposed on each of both sides (both sides in the X-direction) of the cutting tool  441  so that the two rollers in total are disposed. Alternatively, three rollers or five or more rollers may be disposed around the cutting tool  441 . The rotary members that press the outer peripheral surface  11   a  of the liner  11  are not limited to the rollers  425   a,    425   b,    426   a,    426   b.  Ball bearings may be employed, and outer races of the ball bearings may be pressed against the outer peripheral surface  11   a  of the liner  11 . 
     In each of the above-described embodiments, the description has been given of the example in which the weld bead cutting device  100  is for cutting the weld bead FB of the liner  11  that is formed by integrally joining the three resin molded products (the liner portions  21 ,  22 ,  23 ). The disclosure is not limited thereto and can also be applied to a weld bead cutting device for cutting a weld bead of a liner that is formed by integrally joining two resin molded products or a weld bead of a liner that is formed by integrally joining four or more resin molded products. Further, the disclosure is also applicable to a weld bead cutting device for cutting a weld bead of a liner of a tank other than a hydrogen tank. 
     The disclosure is applicable to a weld bead cutting device and a weld bead cutting method configured to remove, by cutting, a weld bead that is generated on the outer circumference of a welding portion of a resin liner.