Abstract:
A smoothing method and a smoothing apparatus uses a belt grinding apparatus, including an endless grinding belt and a press pad that presses the grinding belt against a welded area, and uses this belt grinding apparatus in two different modes after obtaining information on heights of surfaces of two welded members along a weld bead of the two welded members. The first mode corresponds to a bead removing step in which the grinding belt is pressed against a welded area by the press pad to reduce the height of the weld bead. The next mode corresponds to a smoothing step in which the grinding belt presses against the welded area by the press pad while being made to move along the surfaces of the two welded members to smooth the welded area.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method and an apparatus for smoothing a welded area between welded members. 
       BACKGROUND ART 
       [0002]    For instance, a vehicle door frame is formed by butt-welding (corner-welding) a pillar member (upright pillar sash, door frame member) and a sash member (upper sash member, door frame member). In this welding process, TIG (Tungsten Inert Gas) welding or MIG (Metal Inert Gas) welding is generally used. 
         [0003]    In this door frame member welding process, the occurrence of a weld bead (protrusion) at the welding area cannot be avoided. This weld bead appears on design surfaces of the pillar member and the sash member, thus being absolutely necessary to be grounded away to produce a smooth surface, and the weld bead was formerly removed manually by a worker. In addition to a roll-forming product of a metallic material, an extrusion-molded product of an aluminum alloy is also used as a door frame material for the purpose of weight reduction. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Unexamined Patent Publication No. 2000-52211 
         Patent Literature 2: Japanese Unexamined Patent Publication No. 2012-001153 
         Patent Literature 3: Japanese Unexamined Patent Publication JPS58-109263 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    An object of the present invention is to obtain a smoothing method and a smoothing apparatus which enables an automated smoothing operation to be carried out on a welded member(s) that was formerly performed manually. In addition, an object of the present invention is to obtain a smoothing method and a smoothing apparatus which make it possible to perform a smoothing operation on a weld bead within takt (cycle) time, having a predetermined period of time (range). 
       Solution to Problem 
       [0008]    The present invention has been devised while focusing attention on performing a smoothing operation on a welded area after first removing a weld bead (reducing in height), focusing attention on using height information of the surrounding area of the welded area when removing the weld bead, and focusing attention on using the same belt grinding apparatus, which includes an endless grinding belt and a press pad which presses the grinding belt against a welded area, for weld bead removal and for the smoothing operation. 
         [0009]    The present invention is based on the premise that a belt grinding apparatus is used, which includes an endless grinding belt and a press pad which presses the grinding belt against a welded area. This type of belt grinding apparatus has been made known by, e.g., Patent Literature 3. Additionally, in the method according to the present invention, information on the heights of surfaces of two welded members along the weld bead is obtained, and thereafter this belt grinding apparatus is used in two different modes. The first mode corresponds to a bead removing step at which the grinding belt is pressed against a welded area by the press pad to reduce the height of the weld bead. At this time, the grinding belt is made to run at a fixed position, while the press pad is made to move toward and away from the welded area (the surface thereof). The next mode corresponds to a smoothing step at which the grinding belt is made to run and pressed against the welded area by the press pad while being made to move along the surface of the two welded members to smooth the welded area. 
         [0010]    Namely, according to the present invention, to perform the first step of reducing the height of the weld bead, information on the heights of the butt end surfaces of two welded members along the weld bead is detected, and the amount of lowering (projecting) of the grinding belt toward the weld bead is determined so that the weld bead is removed even at the lowest part thereof. 
         [0011]    The method of smoothing a welded area according to the present invention is a method of removing a weld bead between two welded members to smooth the welded area and is characterized by including a step of preparing a belt grinding apparatus, which includes an endless grinding belt and a press pad that presses the grinding belt against the welded area; a measuring step for detecting positions of heights of surfaces of the two welded members along the weld bead; a bead removing step for reducing a height of the weld bead by pressing the grinding belt against the welded area via the press pad while running the grinding belt using information on the positions of the heights of the surfaces of the two welded members that are detected in the measuring step; and a smoothing step for smoothing the welded area by pressing the grinding belt against the welded area via the press pad while running the grinding belt and moving the grinding belt along the surfaces of the two welded members. 
         [0012]    It is desirable for information on heights of a plurality of points along both sides of the weld bead to be obtained in the measuring step. 
         [0013]    It is desirable for the welded area smoothing method to include a step of detecting an angular difference between the surfaces of the two welded members in a direction orthogonal to the weld bead and a in direction along the weld bead; and a step of adjusting angles of the grinding belt and the press pad relative to the surfaces of the two welded members based on the angular difference that is detected in the angular difference detecting step. 
         [0014]    It is desirable for the two welded members to each include a plane portion which extends leftward and rightward from an end of the weld bead in a direction of extension thereof, and for the method to further include a step of grinding and removing a projecting weld bead which projects from the plane portion using the grinding belt and the press pad. 
         [0015]    It is desirable for the two welded members to be uneven members, one end part of which is lower in a direction of formation of the weld bead, and for the bead removing step and the smoothing step to be performed by lifting a lower part of the two welded members. 
         [0016]    It is desirable for a hardness of the press pad used in the bead removing step to be greater than a hardness of the press pad used in the smoothing step. 
         [0017]    It is desirable for a width of the grinding belt and a planar size of the press pad to be each set to a size to cover the length of the weld bead. 
         [0018]    In the bead removing step, it is desirable for at least one of the following grinding conditions to be determined so that the weld bead is removed within a fixed time period: a running speed and a tension of the grinding belt, and a projecting amount and a projecting force of the press pad. 
         [0019]    The two welded members can be, for example, a pillar member and a frame member of a door frame. 
         [0020]    It is further desirable for the method according to the present invention to include performing a joint removing process step using a polisher on surfaces of the two welded members, from which the weld bead has been removed, after the weld bead removing step and the smoothing step has been performed using the grinding belt. 
         [0021]    In the method according to the present invention, it is further desirable to include a step of detecting an angular difference between the surfaces of the two welded members in a direction orthogonal to the weld bead and in a direction along the weld bead, and a step of adjusting an angle of the polisher based on the angular difference that is detected in the angular difference detecting step. 
         [0022]    In another embodiment of the present invention, a welded area smoothing apparatus for removing and smoothing a weld bead of two welded members is provided, including a belt grinding apparatus which includes an endless grinding belt that is driven to run and a press pad that presses the grinding belt against the welded area; a jig for setting the two welded members which include the weld bead; a measuring apparatus which measures positions of heights of surfaces of the two welded members, which are set by the jig, along the weld bead; a position controller which moves the belt grinding apparatus relative to the jig; and a controller which controls the belt grinding apparatus, the measuring apparatus and the position controller. The controller reduces a height of the weld bead by pressing the grinding belt against the welded area via the press pad while running the grinding belt using information on the positions of the heights of the surfaces of the two welded members that are detected by the measuring apparatus, and subsequently, the controller smoothes the welded area by pressing the grinding belt against the welded area via the press pad while running the grinding belt and moving the grinding belt along the surfaces of the two welded members. 
         [0023]    In the welded area smoothing apparatus of the present invention, it is desirable for the measuring apparatus to detect an angular difference between the surfaces of the two welded members in a direction orthogonal to the weld bead and in a direction along the weld bead, and for the controller to adjust angles of the grinding belt and the press pad relative to the surfaces of the two welded members based on the angular difference. 
         [0024]    Furthermore, it is desirable for the two welded members to include a plane portion which extends leftward and rightward from an end of the weld bead in a direction of extension thereof, and for the controller to grind and remove a projecting weld bead which projects from the plane portion using the grinding belt and the press pad. 
         [0025]    It is desirable for the two welded members to be an uneven member, one end of which in a direction of formation of the weld bead is low, and for the jig to include a partial floatation apparatus which lifts a lower part of the two welded members. 
         [0026]    It is desirable for the belt grinding apparatus to include a press pad mechanism which switches the press pad to be used for another press pad during the removing and smoothing of the weld bead. 
         [0027]    In the welded area smoothing apparatus according to the present invention, it is desirable for, in addition to the belt grinding apparatus, a polisher to be further used to perform a joint removing process on surfaces of the two welded members from which the weld bead is removed. 
         [0028]    It is desirable for the polisher to be able to adjust an angle thereof based on an angular difference between the surfaces of the two welded members in a direction orthogonal to the weld bead and in a direction along the weld bead. 
       Advantageous Effects of Invention 
       [0029]    According to the present invention, a belt grinding apparatus which includes an endless grinding belt and a press pad that presses the grinding belt against a welded area is used, the height of the weld bead is reduced by pressing the grinding belt against a welded area via the press pad while making the grinding belt run at the first step, and the welded area is smoothed by pressing the grinding belt against the welded area via the press pad while making the grinding belt run and moving the grinding belt along the surfaces of the two welded members at the second step, and accordingly, the weld bead can be easily removed to smooth the welded area. In addition, the time required to perform the first step and the second step can be controlled, which enables the takt time required for the smoothing operation to become substantially constant and facilitates the automation of the smoothing process. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1(A)  is a plan view of a vehicle door frame to which a method of smoothing a welded area according to the present invention is applied,  FIG. 1(B)  is a perspective view of part B shown in  FIG. 1(A) , and FIGS.  1 (C 1 ),  1 (C 2 ) and  1 (C 3 ) are cross sectional views taken along the lines C 1 -C 1 , C 2 -C 2  and C 3 -C 3  shown in  FIG. 1(A) , respectively; 
           [0031]      FIG. 2  is a perspective view of an embodiment of an apparatus which performs the smoothing method according to the present invention; 
           [0032]      FIG. 3  is a front elevational view of a belt grinding apparatus within the apparatus shown in  FIG. 2 ; 
           [0033]      FIG. 4  is a front elevational view when a support base of the belt grinding apparatus shown in  FIG. 3  has been rotated by 90 degrees about the rotational shaft of a rotating platform to put the apparatus into a height position detection mode, in which the positions of the heights of surfaces of two welded members are detected; 
           [0034]      FIG. 5(A)  is a plan view of a partial floatation apparatus which is provided in a tool in the apparatus shown in  FIG. 2 , and  FIG. 5(B)  is a cross sectional view taken along the line B-B shown in  FIG. 5(A) ; 
           [0035]      FIGS. 6(A) ,  6 (B) and  6 (C) show steps of the smoothing method according to the present invention; 
           [0036]      FIG. 7  is a schematic diagram of an example of the height coordinates of two welded members along a weld bead and the projecting position of a press pad; 
           [0037]      FIG. 8  is a block diagram of the apparatus for smoothing a welded area according to the present invention; 
           [0038]      FIGS. 9(A) ,  9 (B) and  9 (C) are a plan view, a side elevational view and a front elevational view that show a second embodiment of the method of smoothing the welded area according to the present invention; 
           [0039]      FIG. 10  is a control block diagram of the second embodiment; 
           [0040]      FIG. 11  is a plan view showing a third step of the welded area smoothing step (precision grinding process) of the second embodiment; 
           [0041]      FIG. 12  is a conceptual diagram showing an example of a polisher used in a polishing process; 
           [0042]      FIG. 13  is a plan view showing three steps of the polishing process; and 
           [0043]      FIG. 14  is a conceptual diagram showing a corner rounding process of an outline polishing process using the polisher. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0044]      FIG. 1  shows a door frame  10  which includes of a pillar member (front pillar, upright pillar sash, first door frame member)  11  and a frame member (upper sash, second door frame member)  12 , serving as two welded members to which a method of smoothing a welded area according to the present invention is applied. The pillar member  11  and the frame member  12  are each formed of a roll-formed product made of a ferrous material, and a butt-welding edge  11 T of the pillar member  11  and a butt-welding edge  12 T of the frame member  12  are butt-welded (corner-welded), and a weld bead  13  formed on the welding area protrudes and bulges from a surface  11 S of the pillar member  11  and a surface  12 S of the frame member  12 . 
         [0045]      FIG. 2  shows a smoothing apparatus  20  for smoothing a welded area which practices the method according to the present invention, and  FIG. 3  shows a belt grinding apparatus  30  in the smoothing apparatus  20 . The smoothing apparatus  20  is provided with the belt grinding apparatus  30 , a position controller (position control robot)  50  for the belt grinding apparatus  30  and a jig  60  for setting the post-weld door frame  10 . In addition, a laser length-measuring apparatus  40 , serving as a measuring apparatus, which measures the surface heights (Y-coordinates) of the surface  11 S of the pillar member  11  and the surface  12 S of the frame member S 12  is fixed to a support base  31  of the belt grinding apparatus  30 . 
         [0046]    The belt grinding apparatus  30  is supported on the support base  31 , and the position of which is controlled by the position controller  50 ; the basic configuration of the belt grinding apparatus  30  is disclosed in Patent Literature 3. As shown in  FIG. 3 , the belt grinding apparatus  30  is provided with three pulleys: a drive pulley  33  which is driven to rotate at a fixed position by a drive motor  32 , a guide pulley  34  which is rotatably supported at a fixed position, and a tension pulley  36  which is rotatably supported at the end of a swing arm  35   a  of an air swing actuator  35 , and an endless grinding belt (sanding belt)  38  is wound around the peripheries of the drive pulley  33 , the guide pulley  34  and the tension pulley  36 . Driving the drive motor  32  to rotate drive pulley  33  causes the endless grinding belt  38  to run, and tension on the endless grinding belt  38  varies by changing the swing position of the swing arm  35   a  of the air swing actuator  35 . The running speed of the endless grinding belt  38  can be freely set by the drive motor  32 , and the grinding load can be detected via the drive motor  32 . In the present embodiment, a workpiece to be ground (the weld bead  13  of the door frame  10  (and welded areas on the left and right sides thereof)) is ground by a work section belt  38 X (grinding section) positioned between the guide pulley  34  and the tension pulley  36 . During this grinding process, the work section belt  38 X of the belt grinding apparatus  30  is positioned above the jig  60  (the door frame  10  set to the jig  60 ). In addition, a dust collector hopper  39  is disposed on the outer side of the grinding belt  38  of the drive pulley  33  and the guide pulley  34 . 
         [0047]    A press pad mechanism  45  which is supported by the support base  31  is positioned in a space surrounded by the grinding belt  38 . The press pad mechanism  45  is provided with a pair of (plurality of) press pads  46  and  47  and a rotational actuator  48  which selectively positions the press pad  46  and the press pad  47  on the inner side of the grinding belt  38 . The pressing force of each press pad  46  and  47  against the work section belt  38 X (the amount of projection of each press pad  46  and  47  toward the work section belt  38 X) can be adjusted by an air actuator. The press pad  46  can be, e.g., a hard press pad for rough grinding, and the press pad  47  can be, e.g., a soft press pad for fine grinding (for polishing). 
         [0048]    The jig  60  is for holding the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12  so that the surface  11 S and the surface  12 S become substantially parallel to the work section belt  38 X, and is provided with a work accommodating portion  61  which accommodates the door frame  10 . The term. “substantially parallel” means to hold the door frame  10  so that, when the outer sides of the surfaces  11 S and the  12 S are regarded as a plane (flat surface), this imaginary plane of the outer sides of the surfaces  11 S and the  12 S and the work section belt  38 X become parallel to each other because the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12  are not perfectly flat and have a descending gentle curved surface on the inner side (on the window opening side). If the surfaces of the two welded members form a flat surface, the door frame  10  is set on the jig  60  so that this flat surface and the work section belt  38 X become parallel to each other. 
         [0049]    As shown in  FIG. 5 , the jig  60  is provided with a partial floatation apparatus  62  which deforms the descending curved surface on the inner side of the pillar member  11  and the frame member  12  upward for grinding. The partial floatation apparatus  62  is provided with a lifting crank  64  which is rotatable about a shaft  63 . The lifting crank  64  is provided at one end thereof with a lifting arm  64   a  which is positioned to extend over the lower surfaces (bottom surfaces) of the butt-welding edge  11 T of the pillar member  11  and the butt-welding edge  12 T of the frame member  12 , and an air actuator  65  is connected to a drive arm  64   b , which is provided at the other end of the lifting crank  64 . Thrusting out the drive arm  64   b  using the air actuator  65  causes the lifting arm  64   a  to lift portions of the pillar member  11  and the frame member  12  in the close vicinity of the butt-welding edge  11 T and the butt-welding edge  12 T so as to bring these portions closer to a single plane. 
         [0050]    The position controller  50  is a known apparatus for freely controlling the position of the belt grinding apparatus  30  (the support base  31 ) relative to the jig  60  and is provided, on a body base  51  fixed to a floor, with a rotatable base  52  rotatable about a perpendicular axis, and the lower end of a first arm  54  is supported by the rotatable base  52  to be swingable about a horizontal shaft  53 . An extendable second arm  56  is pivoted at the upper end of the first arm  54  via a horizontal shaft  55 , a rotatable base  57  rotatable about a rotational shaft  57 X is mounted onto the end of the second arm  56 , and a support head plate  58  is mounted onto the rotatable base  57 . The position controller  50  can move the support head plate  58  toward any given position and direction and can control the position thereof by rotational movement of the rotatable base  52  about the perpendicular axis, rotational movement of the first arm  54  about the shafts  53  and  55 , expanding, contracting movement of the second arm  56 , and rotational movement of the rotatable base  57  about the rotational shaft  57 X. 
         [0051]    The support head plate  58  is connected to the support base  31  of the belt grinding apparatus  30 , so that the position controller  50  can freely control the position of the belt grinding apparatus  30 . The support base  31  can rotate (swing) about the rotational shaft  57 X (see  FIGS. 3 and 4 ) of the rotatable base  57  (can change in direction at least between the two positions shown in  FIGS. 3 and 4 ), and in this embodiment the laser length-measuring apparatus  40 , which measures the heights of the surface  11 S of the pillar member  11  and the surface  12 S of the frame member S 12 , is supported by the support base  31  using the rotating capability of the rotatable base  57 . Namely, the support base  31  can change the orientation thereof between a grinding position shown in  FIG. 3 , in which the work section belt  38 X of the belt grinding apparatus  30  faces horizontally, and a measuring position shown in  FIG. 4 , in which the work section belt  38 X of the belt grinding apparatus  30  faces vertically; the position controller  50  includes this base direction (orientation) converting apparatus  31 T (see  FIG. 8 ). The laser length-measuring apparatus  40  that is fixed to the support base  31  is provided with two laser length-measuring devices  41  and  42 , and the laser length-measuring devices  41  and  42  face the surface  11 S of the pillar member  11  and the surface  12 S of the pillar member  12 , respectively. The laser length-measuring (distance measuring) devices  41  and  42  are known in the art, in which the laser light emitted from a laser source is split into a measuring light and a reference light by a beam splitter, the measuring light is projected toward the surfaces  11 S and  12 S, and light reflected thereby is detected by a photodetector on one hand, whereas the reference light reflected at a fixed position is made incident on the same photodetector to detect a phase difference between the measuring light and the reference light, and the distance from the reference position of the laser length-measuring device  41  to the surface  11 S and the distance from the reference position of the laser length-measuring device  42  to the surface  12 S are measured based on the phase difference thus detected. 
         [0052]    The position controller  50  is provided with a coordinate detection system which detects the coordinates of the rotational shaft  57 X of the rotatable base  57  in the vertical direction (X-direction), the lateral direction (Y-direction), and the Z-direction which orthogonal to the X-direction and the Y-direction, and a rotational position detection system (90-degree coordinate conversion system) which detects the rotational position of the support base  31 , and is further provided with a detection system which detects the distances from the rotational shaft  57 X to the laser length-measuring devices  41  and  42 , the distance from the rotational shaft  57 X to the work section belt  38 X and the distances from the rotational shaft  57 X to the ends of the press pad  46  and the fine-grinding press pad  47  of the press pad mechanism  45 . Accordingly, the positions of the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12 , the position of the rotational shaft  57 X in the X, Y and Z directions, the position of the work section belt  38 X of the belt grinding apparatus  30  in the X, Y and Z directions, and the positions of the press pad  46  and the fine-grinding press pad  47  of the press pad mechanism  45  in the X, Y and Z directions are correctly detected. 
         [0053]    In the present embodiment, the weld bead  13  of the door frame  10  is removed and smoothed using the smoothing apparatus  20 , which includes the belt grinding apparatus  30  (and the laser length-measuring unit  40 ) and the position controller  50 , in a manner will be discussed hereinafter. 
         [0054]    Measuring Step 
         [0055]    In the first step, the door frame  10  is accommodated (set) in the work accommodating portion  61  of the jig  60 , and in this state the belt grinding apparatus  30  (the support base  31 ) is rotated about the rotational shaft  57 X by 90 degrees using the position controller  50  (the base direction (orientation) changing apparatus  31 T), and the direction of emission of the measuring light from each laser length-measuring device  41  and  42  is directed to travel in the X-direction as shown in  FIG. 4 . Subsequently, the height of the butt-welding edge  11 T of the pillar member  11  along the weld bead  13  and the height of the butt-welding edge  12 T along the weld bead  13  (these heights (Y-coordinates) are of portions which are as close to the weld bead  13  as possible and do not include the weld bead  13 ) are detected by the laser length-measuring devices  41  and  42 . As exaggeratedly shown in FIGS.  1 (C 1 ),  1 (C 2 ) and  1 (C 3 ), the height (Y-coordinate) of the butt-welding edge  11 T of the pillar member  11  along the weld bead  13  and the height (Y-coordinate) of the butt-welding edge  12 T along the weld bead  13  vary. Note that the actual heights (Y-coordinates) of the surface  11 S and the surface  12 S are in the order of micrometers. The reference numeral  14  in  FIG. 6(A)  show four measuring points. Movements of the laser length-measuring devices  41  and  42  in the Z-direction (and the X-direction) are performed by the position controller  50 . 
         [0056]    Measurement of the heights (Y-coordinates) of the surface  11 S and the surface  12 S can be carried out by a contact sensor(s); moreover, a height map can be created by scanning areas of the surfaces  11 S and  12 S around the periphery of the weld bead  13 . In this measurement step, the lowest height (Y-coordinate) among the heights (Y-coordinates) of the surfaces  11 S and  12 S along the weld bead  13  is detected. At this time, the maximum height (Y-coordinate) of the weld bead  13  can be detected. 
         [0057]    Weld Bead Removing (Height Reducing) Step (Rough Grinding Process) 
         [0058]    The second step is for removing the weld bead  13 . In this step, using the position controller  50  (the base direction (orientation) converting apparatus  31 T), the belt grinding apparatus  30  (the support base  31 ) is rotated about a rotational shaft  57 X by 90 degrees, and the work section belt  38 X of the belt grinding apparatus  30  is directed to travel in the X-direction, as shown in  FIG. 3 . In this weld bead removal operation, with the belt grinding apparatus  30  lowered to a fixed position and held thereat by the position controller  50  and with the work section belt  38 X held to be parallel to the surface  11 S of the door frame  10  and the surface  12 S of the frame member  12 , the press pad  46  of the press pad mechanism  45  is made to project toward the weld bead  13  to bring the running grinding belt  38  into contact with the weld bead  13  to grind and remove the weld bead  13  (to reduce the height of the weld bead  13 ). The grinding belt  38  has a sufficient width to remove the entire weld bead  13  at once, which is formed between the butt-welding edge  11 T and the butt-welding edge  12 T (the surface  11 S and the surface  12 S). Namely, as shown in  FIG. 6(A) , the width W of the grinding belt  38  in the Z-direction is set to be greater than the length w of the weld bead  13  in the Z-direction. The widths (diameters) of the press pads  46  and  47  in the Z-direction are also greater than the length w of the weld bead in the Z-direction. Namely, the width of the grinding belt  38  and the planar size of the press pad  46  are each set to a size to cover the length of the weld bead  13  at all times, with consideration of the direction of the weld bead  13 . At this weld bead removing step, the amount of projection of the rough-grinding press pad  46  in the Y-direction is determined from information (Y-coordinate) on the lowest height of the surface of the door frame  10  at the first step. 
         [0059]      FIG. 7  schematically illustrates four measuring points (Y-coordinates) Y1, Y2, Y3 and Y4 on the surface of the door frame  10  and the amount of projection (fully projected position) of the rough-grinding press pad  46  from an initial position thereof in the Y-direction, and an amount of projection Y5 of the press pad  46  is set so that the rough-grinding press pad  46  reaches the lowest measuring point (surface) Y3 of the four measuring points. 
         [0060]    In order for this weld bead removing step to be performed within a fixed period of time (takt time; e.g., three seconds), grinding conditions including the running speed of the grinding belt  38  by the drive motor  32 , the tension of the grinding belt  38  by the air swing actuator  35  and the pressure of the projecting rough-grinding press pad  46  by an air actuator are determined using the aforementioned lowest height (Y-coordinate) of the door frame  10 . For instance, the commencement of contact of the work section belt  38 X with the weld bead  13  (the Y-coordinate of the weld bead  13 ) can be detected from loads exerted on the drive motor  32 , and accordingly, the time from this point to the moment the work section belt  38 X reaches the lowest height (Y-coordinate) of the surface of the door frame  10  (the weld bead removal completion time) is determined to determine the aforementioned grinding conditions. When the height (Y-coordinate) of the weld bead  13  at the measuring step is measured, information on this height can be used to determine the grinding conditions. 
         [0061]    Welded Area Smoothing Step (Fine Grinding Step) 
         [0062]    In the third step, the rough-grinding press pad  46  is switched to the fine-grinding press pad  47  by the rotational actuator  48  of the press pad mechanism  45 . Subsequently, the surface  11 S of the butt-welding edge  11 T and the surface  12 S of the butt-welding edge  12 T that include the removed trace of the weld bead  13  are smoothed by making the fine-grinding press pad  47  project in the Y-direction by the air actuator (while changing the amount of projection of the fine-grinding press pad  47  in the Y-direction as needed) while making the grinding belt  38  run and while making the belt grinding apparatus  30  (the work section belt  38 X) move parallel to the surface  11 S and the surface  12 S of the door frame  10 . In this process, similar to the bead removing step, grinding conditions including the running speed of the grinding belt  38  by the drive motor  32 , the tension of the grinding belt  38  by the air swing actuator  35 , and the pressure of the projecting rough-grinding press pad  46  by an air actuator are varied so that the takt time becomes constant. 
         [0063]    In the above illustrated weld bead removing step and smoothing step, the inner sides of the butt-welding edge  11 T and the butt-welding edge  12 T of the door frame  10  are lifted to become closer to a flat surface using the partial floatation apparatus  62  shown in  FIG. 5 . Although the surface  11 S and the surface  12 S are exaggeratedly shown to be nonparallel to each other in  FIGS. 6(B) and 6(C) , the surface  11 S and the surface  12 S can be regarded as a sufficiently flat surface in practice. This smoothing step makes the trace of the weld bead  13  a flat surface which is smoothly connected to the surface  11 S and the surface  12 S around the trace of the weld bead  13 . At this time, the grinding resistance created by the work section belt  38 X can be detected from loads exerted on the drive motor  32 , and accordingly, grinding conditions including the running speed of the grinding belt  38  by the drive motor  32 , the tension of the grinding belt  38  by the air swing actuator  35 , and the pressure of the projecting rough-grinding press pad  46  by an air actuator are determined so that the grinding resistance becomes an appropriate value and so that the grinding process is performed in a fixed period of time (takt time; e.g., seven seconds). 
         [0064]      FIG. 8  is a block diagram of the apparatus for smoothing the above described welded area. A controller  70  controls the position controller  50  (the base direction (orientation) converting apparatus  31 T), the belt grinding apparatus  30  and the press pad mechanism  45 ; upon the heights (Y-coordinates) of the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12  along the weld bead  13  being detected by the laser length-measuring apparatus  40  (the laser length-measuring devices  41  and  42 ) that is provided on the support base  31  of the belt grinding apparatus  30 , data on the heights thus detected is input, and the belt grinding apparatus  30  and the press pad mechanism  45  are controlled based on the input signal. Additionally, a data memory  71  for a partial floatation operation, which supplies an operation signal to the partial floatation apparatus  62  in accordance with the shapes of the pillar member  11  and the frame member  12 , is incorporated in the controller  70 . 
         [0065]    It is desirable that the partial floatation apparatus  62  be installed in the case where the two welded members are two members (the pillar member  11  and the frame member  12  in the present embodiment) whose surfaces to be ground are not flat surfaces (partly curved surfaces); however, the partial floatation apparatus  62  is unnecessary when surfaces of the two members which are to be ground are flat surfaces. Additionally, in the above illustrated embodiment, a more desirable grinding operation can be performed because the rough-grinding press pad  46  of the press pad mechanism  45  is used at the weld bead removing step and the fine-grinding press pad  47  of the press pad mechanism  45  is used at the smoothing step; however, both can also be performed using the same press pad. Conversely, it is possible for other types of press pads to be prepared and selectively used. 
         [0066]    The above illustrated embodiment is an embodiment in which the weld bead  13  is removed by performing the above described weld bead removing (height reducing) step (rough grinding process) and the welded area smoothing step (fine grinding process) on the assumption that no step exists between the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12 . However, in an actual welding operation, the occurrence of a small step (difference in level) between the surface  11 S and the surface  12 S is inevitable.  FIG. 9  illustrates the angular difference (inclination, θ1) ( FIG. 9C ) in a direction orthogonal to the weld bead  13  between the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12  and the angular difference (inclination, θ2) ( FIG. 9B ) in a direction of extension of the weld bead  13  between the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12 . The difference in actual height between the surface  11 S and the surface  12 S is in the order of micrometers, thus being exaggeratedly shown in the drawings. In  FIG. 9 , the positions of the heights of the positions of the butt-welding edge  11 T of the pillar member  11  and the butt-welding edge  12 T of the frame member  12  are made to coincide with each other on the inner peripheral side (on the window opening side). A second embodiment according to the present invention shown in  FIGS. 9 through 11  is different from the first embodiment mainly in regard to points (1), (2) and (3) which will be discussed hereinafter. 
         [0067]    (1) The weld bead  13  is removed by the above-mentioned rough grinding process (and the above-mentioned fine grinding process) while taking into consideration the fact that an angular difference (inclination, θ1) occurs in a direction orthogonal to the weld bead  13  between the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12 , and the angular difference (inclination, θ2) occurs in a direction of extension of the weld bead  13  between the surface  11 S of the pillar member  11  and the surface  12 S of the frame member  12  (the surface  11 S and the surface  12 S do not exactly lie in a single plane). In addition, the fine grinding process is performed a plurality of times with the work section belt  38 X (the fine-grinding press pad  47 ) in different movement directions. 
         [0068]    (2) An upper edge (plane portion)  11 F which is flush with an upper edge (plane portion)  12 F of the frame member  12  is formed at the upper end of the pillar member  11 , and a projecting bead  13 F which projects from the upper edges  12 F and  11 F is also removed. 
         [0069]    (3) After the weld bead  13  and the projecting bead  13 F are removed, a polishing process (joint removing process) is performed. 
         [0070]    In the present embodiment, the belt grinding apparatus  30  is made to swing about the shaft  55  or (and) the rotational shaft  57 X of the position controller  50 , while taking consideration of the angular differences θ1 and θ2, so that the difference between the angle between the surface  11 S and the work section belt  38 X (the end pressing plane of the rough-grinding press pad  46  or the fine-grinding press pad  47 ) and the angle between the surface  12 S and the work section belt  38 X (the end pressing plane of the rough-grinding press pad  46  or the fine-grinding press pad  47 ) is reduced, and the above-mentioned rough grinding process (and the above-mentioned fine-grinding process) is performed in this swinging state. The direction of the work section belt  38 X after adjustment that is defined in consideration of the angular difference θ1 is designated by  38 X θ1 in  FIG. 9(C) , and the direction of the work section belt  38 X after adjustment that is defined in consideration of the angular difference θ2 is designated by  38 X θ2 in  FIG. 9(B) . 
         [0071]    In this embodiment, after the work section belt  38 X (the rough-grinding press pad  46 ) is made to tilt by  38 X θ1 and  38 X θ2 relative to the surface  11 S and the surface  12 S as shown in  FIGS. 9(B) and 9(C) , the amount of projection of the rough-grinding press pad  46  is determined using information on the height measuring points  14  on the surface  11 S and the surface  12 S, and the rough grinding process is performed. In the rough grinding process, similar to the first embodiment, the amount of projection of the rough-grinding press pad  46  is set so that the work section belt  38 X reaches the lowest measuring point (surface) among the four height measuring points  14 . 
         [0072]    The fine grinding process that is performed with the work section belt  38 X and the fine-grinding press pad  47  is performed in three steps as shown in  FIG. 11 . The first fine grinding step (P) is a process performed by moving the work section belt  38 X and the fine-grinding press pad  47  in a direction P along the (removed) weld bead  13  on the surface  11 S and the surface  12 S, the second fine grinding step (Q) is a process performed by moving the work section belt  38 X and the fine-grinding press pad  47  in a direction Q along the lengthwise direction of the pillar member  11 , and the third fine grinding step (R) is a process performed by moving the work section belt  38 X and the fine-grinding press pad  47  in a direction R along the lengthwise direction of the frame member  12 . As seen above, the surface  11 S and the surface  12 S can further be smoothed by performing the fine grinding process in three steps. 
         [0073]    The work section belt  38 X (and the fine-grinding press pad  47 ) is held at an angle in consideration of both the angle  38 X θ1 and the angle  38 X θ2 at the first fine grinding step (P) and put into action, is held at the angle  38 X θ1 and put into action at the second fine grinding step (Q) and is held at the angle  38 X θ2 and put into action at the third fine grinding step (R). 
         [0074]    In the embodiment shown in  FIG. 9 , an outer-profile grinding process for removing the projecting bead  13 F of the weld bead  13  is additionally performed. In the outer-profile grinding process, first of all, in the measuring step performed at the four height measuring points  14 , information on the planar positions in  FIG. 9(A)  of a measuring edge  14   a  and a measuring edge  14   b  on the upper edge  12 F is obtained using a linear laser length-measuring apparatus, as a laser length-measuring apparatus, with which height information can be obtained along a linear measuring line. Based on this planar position information, the angle (direction) D of the work section belt  38 X (and the rough-grinding press pad  46  or the fine-grinding press pad  47 ) is set by the position controller  50  to be parallel to a line (plane) which connects the measuring edges  14   a  and  14   b . In  FIG. 9(A) , the direction of the work section belt  38 X after adjustment that is defined in consideration of the angle D is designated by XP. Performing a belt grinding operation over the upper edge  12 F and the upper edge  11 F with the direction of the work section belt  38 X set in this manner makes it possible to remove the projecting bead  13 F in parallel with the upper edge  12 F and the upper edge  11 F. 
         [0075]      FIG. 10  is a control block diagram of the second embodiment. At a measuring step  100 , the heights of the surface  11 S and the surface  12 S at the four height measuring points  14  surrounding the weld bead  13  (and the planar positions of the measuring edge  14   a  and the measuring edge  14   b ) are measured (detected), and a height calculation Y, an angular difference calculation θ1 and θ2, and an angle calculation D are performed. Based on these calculations, the direction of the work section belt  38 X of the belt grinding apparatus  30  (and the rough-grinding press pad  46  or the fine-grinding press pad  47 ) is set, and a rough grinding process  101 , a fine grinding process (P, Q, R)  102  and an outer-profile grinding process  103  are performed. The pad pressing pressure and the belt rotational speed at each process can be freely (individually) controlled. The three-step processes P, Q and R, in the fine grinding process can be performed on the same condition or different conditions. 
         [0076]      FIGS. 12 through 14  show a polishing process (joint removing process) which is performed after the above described belt grinding process, which is performed using the grinding belt  38  (the work section belt  38 X).  FIG. 12  is a conceptual diagram of a polisher  80 . The polisher  80  in this embodiment is a double-action type which performs rotational motion and eccentric rotational motion and is provided with a polisher body  81 , an eccentric rotary shaft  82  which projects from the polisher body  81 , a polishing rotor  83  which is mounted to the end of the eccentric rotary shaft  82 , and a polishing paper  84  which is mounted (dismounted and replaced) to the polishing rotor  83 . The eccentric rotary shaft  82  eccentrically rotates about a rotational center  82 X while rotating on the axis of the eccentric rotary shaft  82 . A polishing plane presented by the polishing rotor  83  (the polishing paper  84 ) is designated by  84 P. As a double-action type of polisher, a type which performs rotational motion and vibrating motion (axially reciprocating motion) is known, or a single-action type which performs only rotational motion is also known; either type can be selected and used. 
         [0077]    Since the polisher  80  is supported, in a similar manner to that of the belt grinding apparatus  30 , by another support head plate  58  of the position controller  50 , the polisher  80  can be oriented at any given direction. The simplest method of polishing the surface  11 S and the surface  12 S using the polisher  80  is that in which a process of grinding the surfaces of the butt-welding edge  11 T and the butt-welding edge  12 T is carried out with the rotational plane of the polishing rotor  83  (the polishing paper  84 ) set to be substantially parallel to the surface  11 S and the surface  12 S. As shown in  FIG. 13 , this polishing desirably includes a first joint removing process in which the polishing rotor  83  (the polishing paper  84 ) is moved on the surface  11 S and the surface  12 S in a Q-direction along the lengthwise direction of the pillar member  11 , a second joint removing process in which the polishing rotor  83  (the polishing paper  84 ) is moved on the surface  11 S and the surface  12 S in an R-direction along the lengthwise direction of the frame member  12 , and a third joint removing process in which the polishing rotor  83  (the polishing paper  84 ) is moved on the surface  11 S and the surface  12 S linearly in an S-direction along the upper edge  12 F and the upper edge  11 F after the polishing plane  84 P of the polishing rotor  83  (the polishing paper  84 ) is set parallel to the upper end  12 F and the upper end  11 F from which the projecting bead  13   f  has been removed. It is desirable for the polishing diameter of the polishing rotor  83  (the polishing paper  84 ) to be made sufficiently greater than the widths of the pillar member  11  and the frame member  12 . 
         [0078]    As described above, the angular difference (θ1) in a direction orthogonal to the butt-welding edge  11 T and the butt-welding edge  12 T (the weld bead  13 ) exists between the surface  11 S and the surface  12 S and the angular difference (θ2) in a direction of extension of the weld bead  13  exists between the surface  11 S and the surface  12 S. In the joint removing process and the second joint removing process of the controller  70 , similar to the above described grinding process, the direction of the polishing plane  84 P of the polishing rotor  83  (polishing paper  84 ) can be controlled based on information on the angular differences θ1 and θ2. 
         [0079]      FIG. 14  is a conceptual diagram showing a corner rounding process which can be optionally performed. An edge E on the vehicle exterior side of the upper edge  11 F and  12   f  is rounded by applying a swing motion of the polishing rotor  83  (the polishing paper  84 ) of the polisher  80  about the edge E while rotating the polishing rotor  83  (the polishing paper  84 ) with the polishing rotor  83  (the polishing paper  84 ) brought into contact with the edge E, and as necessary, by moving the polishing rotor  83  (the polishing paper  84 ) in the lengthwise (extension) direction of the upper edge  11 F and the upper edge  12 F (in a direction perpendicular to the sheet). 
         [0080]    The above described illustrates the pillar member  11  and the frame member  12  of the door frame  10  as two welded members, and the present invention has been applied to a welded corner between the pillar member  11  and the frame member  12 ; however, the present invention can also be applied to other two welded members. 
       INDUSTRIAL APPLICABILITY 
       [0081]    The method and apparatus for smoothing welded members according to the present invention are applicable to a vehicle door frame and are also widely applicable to techniques of smoothing a welded area of two welded members. 
       REFERENCE SIGN LIST 
       [0000]    
       
           10  Door frame 
           11  Pillar member (two welded members) 
           12  Frame member (two welded members) 
           11 T  12 T Butt-welding edge 
           11 S  12 S Surface 
           11 F and  12 F Upper edge (plane portion) 
           13  Weld bead 
           13 F Projecting bead 
           14  Height measuring point 
           20  Smoothing mechanism 
           30  Belt grinding apparatus 
           31  Support base 
           32  Drive motor 
           33  Drive pulley 
           34  Guide pulley 
           35  Air swing actuator 
           36  Tension pulley 
           38  Grinding belt 
           38 X Work section belt 
           40  Laser length-measuring unit (measuring apparatus) 
           41   42  Laser length-measuring device 
           45  Press pad mechanism 
           46  Press pad (for use in rough grinding) 
           47  Press pad (for use in fine grinding) 
           43  Rotational actuator 
           50  Position controller 
           51  Body base 
           52  Rotatable base 
           53   55  Shaft 
           54  First arm 
           56  Second arm 
           57  Rotatable base 
           57 X Rotational shaft 
           58  Support head plate 
           60  Jig 
           61  Work accommodating portion 
           62  Partial floatation apparatus 
           63  Shaft 
           64  Lifting crank 
           64   a  Lifting arm 
           64   b  Drive arm 
           65  Air actuator 
           70  Controller 
           80  Polisher 
           81  Polisher body 
           82  Eccentric rotary shaft 
           83  Polishing rotor 
           84  Polishing paper 
           100  Measuring step 
           101  Rough grinding process 
           102  Fine grinding process 
           103  Outer-profile grinding process