Abstract:
There is provided a method and a device capable of holding a sheet-like workpiece without wrinkles. The sheet-like workpiece holding method includes mounting the sheet-like workpiece such that almost no tensile force is applied thereon on a machining table, and pressing out wrinkles of the sheet-like workpiece by lowering a pressing member whose surface facing to the workpiece protrudes in the shape of a convex lens toward the workpiece so that the workpiece is pressed against the machining table. The method also includes retaining the sheet-like workpiece on the machining table using suction while continuously pressing the sheet-like workpiece with the pressing member and releasing the pressing force of the pressing member while retaining the sheet-like workpiece.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method and a device for holding a sheet-like workpiece by rolling out the sheet-like workpiece wound in a roll to hold a part thereof on a flat table. The invention is suitably applicable to a laser machining apparatus for machining a flexible printed board for example. 
   2. Description of the Prior Art 
   As a machining apparatus for machining a sheet-like workpiece, there has been known a laser machining apparatus having, successively, an unwinding unit for unwinding a non-machined material wound in a roll, a machining unit having a machining section (laser head) for drilling the non-machined material and a take-up unit for taking up the finished material in a roll as disclosed in Japanese Patent Laid-Open No. 2004-195510 for example. The laser machining apparatus also includes a machining table disposed so as to be movable relative to a main frame of the machining apparatus such that a plurality of blocks of the non-machined material can be moved and positioned in a longitudinal direction of the material for machining by the machining section. The laser machining apparatus also includes clamp means disposed in a body of the machining table and operates so as to clamp the non-machined material with respect to the machining table when the machining table moves from a starting position to an ending position and to release the non-machined material from the machining table when the machining table returns to the starting position. Moreover, the laser machining apparatus includes relative position fixing means that operate to fix relative positions of the non-machined material to the machining apparatus before releasing the non-machined material from the clamp means when the machining table reaches the end position and so as to release the fixed state of the relative position of the non-machined material to the machining apparatus after clamping the non-machined material with the clamping means when the machining table returns to the starting position. 
   This technology makes it possible to prevent the position of a printed board, i.e., a sheet-like workpiece, from deviating from the laser head and hence improves machining efficiency. 
   It is noted that the sheet-like printed board is often positioned on the machining table by applying a slight tensile force between a feed roll and a take-up roll, and by fixing the printed board on the machining table using suction or fixtures such as a clamper. 
   There has also been known a laser machining apparatus having at least a pair of clamps for holding both ends of a material to be machined and a tensioning unit for applying bias between the pair of clamps in a direction of relatively separating from each other to apply a tensile force to the non-machined material as disclosed in Japanese Patent Laid-Open No. 1998-296473 for example. 
   Since this technology allows the material to be kept flat even if it is apt to curl, it allows machining accuracy to be improved. 
   Moreover, in laser drilling a printed board on which copper foil is provided, etching is carried out before the drilling and a thickness of the printed board becomes uneven due to etching. Therefore, the printed board wound in a roll after etching causes wrinkles formed almost in parallel with a running direction the printed board. 
   The wrinkles formed almost in parallel with the running direction are unable to be removed even if a tensile force is applied in the running direction of the printed board. Therefore, the printed board on which etching process has been carried out is held on the table while having the wrinkles. 
   Although no hole can be machined, causing defective machining, at the wrinkled part because it is out of focus in case of laser machining, no consideration has been given to the wrinkles running almost in parallel with the running direction of the sheet-like workpiece in Japanese Patent Laid-Open Nos. 2004-195510 and 1998-296473. 
   Accordingly, it is an object of the invention to provide a method and a device capable of holding a sheet-like workpiece on a table without wrinkles. 
   This object may be achieved through the combination of features described in independent claims of the invention. Dependent claims thereof specify preferable embodiments of the invention. 
   BRIEF SUMMARY OF THE INVENTION 
   In order to solve the above-mentioned problem, according to the invention, there is provided a method for holding a sheet-like workpiece by rolling out the sheet-like workpiece wound in a roll so as to hold a part thereof on a flat table. The method includes mounting the sheet-like workpiece on the table (see  FIG. 3A ), pressing out wrinkles of the sheet-like workpiece by pressing the mounted sheet-like workpiece with a pressing member from a side (upper side) opposite from the table (see  FIG. 3B ), retaining the sheet-like workpiece on the table (by means of suction for example) while continuously pressing the sheet-like workpiece (see  FIG. 3C ) and releasing the pressing force of the pressing member while retaining the sheet-like workpiece. 
   According to the invention, there is also provided a device for holding a sheet-like workpiece having a flat table having retaining means (suction means for example) for retaining the sheet-like workpiece and a pressing member. The pressing member is disposed so as to face to the table and which is capable of contacting the table. The device presses out wrinkles of the sheet-like workpiece by pressing the sheet-like workpiece with the pressing member from a side opposite from the table while mounting the sheet-like workpiece on the table and retains the sheet-like workpiece on the table by the retaining means while pressing the sheet-like workpiece. 
   The invention allows the sheet-like workpiece to be fixed on the table without wrinkles, so that it allows the machining quality to be improved. 
   It is noted that the summary of the invention described above does not necessarily describe all necessary features of the invention. The invention may also be a sub-combination of the features described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front partial sectional view of a laser machining apparatus to which the invention is applied. 
       FIG. 2  is an enlarged view of a part A in  FIG. 1 . 
       FIGS. 3A through 3K  illustrate operation of the laser machining apparatus to which the invention is applied and show different states thereof. 
       FIG. 4  is a schematic diagram showing directions of force of a pressing member acting on a workpiece. 
       FIGS. 5A and 5B  are schematic diagrams showing directions of force of the pressing member on a workpiece, wherein  FIGS. 5A and 5B  show different embodiments. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention will now be described based on preferred embodiments shown in the drawings, which do not intend to limit the scope of the invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiments are not necessarily essential to the invention. 
     FIG. 1  is a front partial sectional view of a laser machining apparatus  50 .  FIG. 2  is an enlarged view of a part A in  FIG. 1 .  FIGS. 3A through 3K  illustrate operation of the laser machining apparatus  50 . 
   In the laser machining apparatus  50 , a gate-like column  30  is fixedly installed on a bed  1 . Disposed on the column  30  are a laser oscillator  31 , a plurality of mirrors  32  (two in the figure), a pair of optical mirrors  33  and an fθ lens  34 . 
   A linear guide  2  is disposed on the upper face of the bed  1 , so that an X table  3  is movable on the bed  1  in the X direction. A linear guide  4  is disposed on the upper face of the X table  3 , so that a Y table (mobile table)  5  is movable on the X table  3  in a Y direction. Accordingly, from the configuration described above, the Y table  5  is movable in the X and Y directions with respect to the bed  1 . 
   Disposed on the upper face of the Y table  5  are a machining table  6  and a reel holder  10  as shown in  FIG. 2 . A channel  6   m  having a transverse width wider than a width of a sheet-like workpiece (referred to simply as a workpiece hereinafter) w, such as a flexible printed board, is formed on a lower face of the machining table  6  in the X direction. A plurality of holes connected with a hollow section not shown within the machining table  6  are formed on the upper face of the machining table  6 . The hollow section (not shown) within the machining table  6  is connected with a vacuum source (not shown). These components compose retaining means. The reel holder  10  is provided with a feed reel  11 , a take-up reel  12 , guide rollers  13 ,  14  and  15 , clampers  16  and  17 , a turning roller  18  and a workpiece conveying unit (moving means)  20 . 
   The feed roll  40 , in which non-finished workpiece w is wound in a roll, is held by the feed reel  11 . The feed reel  11  is held by the reel holder  10  and is rotated by a motor (not shown). A bottom  11   b  of the feed reel  11  is positioned under a top  13   t  of the guide roller  13  adjacent thereto. Accordingly, the feed reel can feed the workpiece w when driven by the motor (not shown) (feed side roll holder). 
   A take-up roll  41  collects the finished workpiece w and takes it up in a roll. The take-up roll  41  is held by the take-up reel  12 . The take-up reel  12  is held by the reel holder  10  and is rotated by a motor (not shown). The take-up reel  12  is disposed at the position where a bottom  41   b  of the take-up roll  41  is higher than a bottom  14   b  of the guide roller  14  adjacent to the take-up roll  41 . Accordingly, the take-up reel  12  can take up the workpiece w when driven by the motor (not shown) (take-up side roll holder). 
   The reel holder  10  supports the rotatable guide roller  13  so that a top  13   t  thereof is higher than a surface (upper face) of the machining table  6 . The reel holder  10  also supports the rotatable guide rollers  14  and  15  so that their bottoms  14   b  and  15   b  are lower than a bottom face of the channel  6   m.    
   The clampers  16  and  17  are composed of receptors  16   u  and  17   u  and pressers  16   p  and  17   p . Pressers  16   p  and  17   p  are disposed so as to face the receptors  16   u  and  17   u  and are movable in the Z direction (in the vertical direction in the figure) by means (not shown). A lower end of the receptor  16   u  is set at its standby position such that its upper face is located at a position lower than the surface of the machining table  6 . When the receptor  16   u  is located at its upper position, the upper face is located at the same height with the top  13   t  of the guide roller  13 , i.e., above the surface of the machining table  6 . Moreover, a lower end of the presser  16   p  is set slightly under the upper face of the receptor  16   u  in the standby position so that the lower face of the presser  16   p  can press the upper face of the receptor  16   u . A lower end of the presser  17   p  is also set slightly under the upper face of the receptor  17   u  so that the lower face of the presser  17   p  can press the upper face of the receptor  17   u . The reel holder  10  supports the rotatable turning roller  18  so that a top  18   t  thereof is set on the same height with the top  13   t  of the guide roller  13 . 
   The workpiece conveying unit  20  may be freely moved and positioned in the X direction with respect to the reel holder  10  by means of a motor and a guide rail mechanism (not shown). The workpiece conveying unit  20  supports a clamper  21 . The clamper  21  is composed of a presser  21   p  and a receptor  21   u  movable in the vertical direction. A standby position of the receptor  21   u  is set at a position whose upper face is lower than the upper face of the machining table  6  as shown by a solid line in  FIG. 2 , and its upper position is set on the same height with the top  13   t  of the guide roller  13  and the top  18   t  of the turning roller  18 . Moreover, the standby position of the presser  21   p  is set such that a lower face thereof is higher than the top  13   t  of the guide roller  13  and the top  18   t  of the turning roller  18 . A lower end thereof is set slightly below the upper face of the receptor  21   u  located at its upper position so that the lower face of the presser  21   p  can press the upper face of the receptor  21   u  located at its upper position. It is noted that standby position of the workpiece conveying unit  20  in the X direction is set at a movable left end shown by solid lines in the figure and its movable right end is position shown by dashed lines in the figure. 
   As shown in  FIG. 1 , a pressing plate  60  is disposed in the column  30  so as to face the Y table  5 . A pressing member  61 , made from an elastic member, is fixed under the pressing plate  60 . A pressing surface (facing the Y table  5 ) of the pressing member  61  is a curved surface convex to the machining table  6  (i.e., a convex-shaped curved surface), or more specifically, is a curved surface formed in the shape of a convex lens (see downwardly-facing pressing surface of pressing member  61  in  FIG. 1 ) and having an apex at the center of the X and Y directions (axes) of the pressing plate  60 . The pressing plate  60  may be moved and positioned in the vertical (Z) direction by a lift  62  held in the column  30 . 
   Next, an operation of the laser machining apparatus  50  will be explained. A situation is considered where a non-finished workpiece w held in the feed roll  40  has wrinkles in the running direction (X direction). 
   At first, arrangements for this operation will be explained. That is, while opening all of the clamps  16 ,  17  and  21  in advance such that the receptors  16   u  and  21   u  are at their standby positions and the pressers  16   p ,  17   p  and  21   p  are at their upper positions, the feed roll  40  is put on the feed reel  11 . The workpiece w is wound around the turning roller  18  and is passed through the channel  6   m  of the machining table  6  and its end is fixed to the take-up reel  12  (the take-up roll  41 ). 
   Next, the presser  16   p  is lowered, while applying a slight clockwise torque to the feed reel  11  and the take-up reel  12 , to hold the workpiece w by the clamper  16  while smoothing out wrinkles in the direction orthogonal to the running direction. Moreover, the presser  17   p  is lowered so that the clamper  17  holds the workpiece w. Then, the workpiece w is fixed on the upper face of the machining table  6  in a state in which tensile force is applied slightly thereon in the running direction, as shown in  FIG. 3A . 
   Although the wrinkles in the part of the workpiece w clamped by the clampers  16  and  17  are smoothed out, the wrinkles around the center of the machining table  6  are not. 
   Next, after positioning the center of the machining table  6  to the center of the pressing member  61  by moving the Y table  5 , the pressing plate  60  is lowered to a point where the surface of the pressing member  61  becomes almost flat, as shown in  FIG. 3B . It is noted that the whole area of the workpiece w to be machined contacts and is pressed by the pressing member  61 . After the pressing member  61  contacts the workpiece w, an area of the pressing member  61  contacts the workpiece w and expands concentrically, as indicated by arrows in  FIG. 4 , such that the wrinkles formed on the workpiece w are pressed out. 
   Next, a vacuum source (not shown) is put into operation while lowering the pressing plate  60  so that the workpiece w is sucked to the surface of the machining table  6 , as shown in  FIG. 3C . As a result, the workpiece w is fixed on the surface of the machining table  6  without wrinkles. 
   After fixing the workpiece was described above, machining is carried out. That is, the machining table  6  is moved to position an area to be machined with respect to the fθ lens  34 , and the laser oscillator  31  is put into operation such that a laser beam outputted from the laser oscillator  31  is guided to the optical mirror  33  via the mirrors  32 . Then, the laser beam is positioned by the optical mirror  33  and is caused to be incident on the workpiece w by the fθ lens  34  while vertically setting an optical axis of the laser beam to machine the workpiece w. After ending the machining of the machining area determined by the fθ lens  34 , the X table  3  or the Y table  5  is moved to machine a next machining area. 
   Next, a step for moving the workpiece after ending machining will be explained. After ending machining, the vacuum source (not shown) is turned off and the presser  16   p  is raised. Then, the clamper  21  is put into operation as shown in  FIG. 3D . That is, after raising the receptor  21   u , the presser  21   p  is lowered so as to hold the workpiece w by the presser  21   p  and the receptor  21   u.    
   Next, the presser  17   p  is raised as shown in  FIG. 3E . As a result, the workpiece w is positioned at a height of the top  13   t  of the guide roller  13  and the top  18   t  of the turning roller  18 . 
   In this state, the workpiece conveying unit  20  is moved to the right in the figure by a desirable distance, as shown in  FIG. 3F . It is noted that at this time, the portion of workpiece w whose machining has been finished is taken up by the take-up reel  12  while feeding the workpiece w by the feed reel  11 . 
   Next, after moving the receptor  16   u  to its upper position, the presser  16   p  is lowered, as shown in  FIG. 3G , to hold the workpiece w by the clamper  16 . 
   Next, the clamper  21  is released. At this time, the presser  21   p  is moved to its upper position and the receptor  21   u  is moved to a position where its upper face does not contact with the workpiece w and where it does not contact with the upper face of the machining table  6 . Then, the workpiece conveying unit  20 , i.e., the clamper  21 , is returned to its standby position as shown in  FIG. 3H . 
   Next, after positioning the receptor  21   u  to its standby position, as shown in  FIG. 3I , the presser  17   p  is lowered to hold the workpiece w by the clamper  17 , as shown in  FIG. 3J . Then, the clamper  16  is released as shown in  FIG. 3K . Then, after positioning the receptor  16   u  to its standby position, the presser  16   p  is lowered to hold the workpiece w by the clamper  16  (see  FIG. 3A ). These steps are repeatedly carried out thereafter. 
   During the steps described above and during machining, the feed reel  11  and the take-up reel  12  are driven with a certain range of torque that will have no adverse effect on the workpiece w. Tensile force is applied to the workpiece w so that the workpiece w does not sag. It is noted that the tensile force may be applied by biasing the rollers  13  and  14 , the turning roller  18  and others in predetermined directions by springs or the like. 
   As described above, because the laser machining apparatus  50  adopting the inventive sheet-like workpiece holding method allows the workpiece w to be machined without wrinkles, machining may be carried out in high quality. 
   Moreover, according to the present embodiment, because the feed reel and the take-up reel are disposed on one side on the machining table  6 , no space for forming a free loop of the sheet-like workpiece is required and an installation area of the whole laser machining apparatus  50  may be reduced. Further, because this configuration requires fewer components, the control can be made readily. 
   Further, because the feed reel and the take-up reel are disposed on one side on the machining table  6 , the installation area of the whole laser machining apparatus  50  may be reduced as compared to a case of disposing them on both sides of the machining table  6 . 
   Moreover, the invention allows the wrinkles to be pressed out even if the wrinkles run in the direction other than the running direction of the workpiece w. It is noted that although the surface of the pressing member  61  is formed into the shape of a convex lens so as to have its apex at the center of the X and Y directions of the pressing plate, it may be a cylindrical face whose axis is disposed in parallel with the running direction (X direction). Thereby, because a contact area of the pressing member  61  with the workpiece w expands gradually in a width direction as shown in  FIG. 5A , the wrinkles caused in the workpiece w may be pressed out. 
   The wrinkles of the workpiece w may also be pressed out in the same manner with the case described above by disposing the axis of the cylindrical face orthogonally or obliquely to the running direction as shown in  FIG. 5B . 
   It is noted that the shape of the surface of the pressing member  61  may be any shape as long as it can increase its contact area with the workpiece w gradually from the center part to the peripheral part, such as a part of an ellipsoid. 
   Furthermore, the pressing member  61  may be made from a solid elastic member or may have a space in which a fluid is filled. The pressing member  61  may be also a porous elastic member, e.g., sponge. 
   When the pressing member  61  is made from sponge, the pressing member  61  may be separated readily from the workpiece w after sucking the workpiece w by the Y table  5 , in the step in  FIG. 3C , even if through holes are formed in the workpiece w. 
   An adhesive layer may be provided on the surface of the pressing member  61  to provide a function of removing dust on the surface of the workpiece w. 
   The invention is applicable not only to the case of machining printed boards but also to a case of machining other sheet-like workpieces. 
   Although the invention has been described by way of the exemplary embodiments, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and scope of the invention. It is obvious from the definition of the appended claims that the embodiments with such modifications also belong to the scope of the invention.