Abstract:
A vehicle body transfer machine transfers a vehicle body along a transfer path by using a transfer truck with which the vehicle body is supported, wherein the transfer truck is returned to an initial starting position of the transfer path for a repeated use when transfer of the vehicle body is terminated. The vehicle body transfer machine comprises a jig change-over stage located before the initial starting position of the transfer path, a plurality of locator jigs including an upwardly directed locating pin, a plurality of lock units, an unlock-operating unit, and a jig change-over unit including a socket portion engageable with the locating pin of the corresponding one of the plurality of locator jigs. The socket portion is moveable toward the locating pin to be brought into engagement therewith under a first unlock condition established when the unlock-operating unit unlock-operates the plurality of lock units, which is correlated with the horizontal two directions, of the corresponding one of the plurality of locator jigs to perform a relative positioning in the two horizontal directions between the jig change-over unit and the corresponding one of the plurality of locator jigs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a vehicle body transfer machine and a method thereof for use in a vehicle body assembly line of an automobile and more particularly, to a vehicle body transfer machine of a general-purpose type and a method thereof specifically suited for transferring vehicle bodies of plural vehicle&#39;s models in a so-called mixed flow manufacturing system.  
           [0002]    Japanese Patent Publication No. 2745841 discloses a vehicle body transfer machine of a general-purpose type.  
           [0003]    Such a vehicle body transfer machine is generally constructed of a vehicle body assembly line which includes a plurality of work stages located in a spaced relationship with a given interval, with a final stage and an initial stage being connected to one another with a return line to form a circulated line to enable a transfer truck, which supports the vehicle body, to be circulated in use. In such a structure, the transfer truck is constructed of a plurality of multi-axis units each with an operating freedom in orthogonal three axes, with each multi-axis unit carrying at its distal end a locating pin whose three-dimensional position can be substantially changed over to an arbitrary selected position. The circulated line is constructed of a change-over stage mounted with a change-over robot. With such a structure, when transferring the vehicle bodies of another vehicle&#39;s model using the transfer truck, the change-over unit operates to release the coupling force (restricting force) of brake units adapted to restrict the operating freedoms of respective multi-axis units and subsequently to allow the change-over robot in the change-over stage to shift the locating pin of each multi-axis unit to an arbitrary position to be positioned while retaining the locating pin. Then, the operating freedom of each multi-axis unit is restricted again, completing the change-over operation of the work position of each locating pin.  
         SUMMARY OF THE INVENTION  
         [0004]    More specifically, in such a structure of the vehicle transfer machine, each multi-axis unit includes air cylinders contained therein for restoring original positions of respective operating freedoms in the orthogonal three axes. With such an arrangement, when releasing the coupling force (the restricting force) of each brake unit by supplying compressed air thereto from outside during the change-over operation of the locating pin, simultaneously, the three air cylinders are operated to cause the locating pin to move to original positions correlated with respective directions to be restored at the original point at once. Thus, it is required for the vehicle body transfer machine to undesirably employ the air cylinders specific for respective operating freedoms to restore the original point. This results in an increase in the number of component parts, with a resultant complicated structure and large size in structure.  
           [0005]    Further, when changing over the position of the locating pin, since an annular recessed portion formed near the locating pin is gripped with the robot&#39;s hand and is moved in the respective positions at a stretch using the operating freedom in the orthogonal three axes in the X-, Y- and Z-directions, there is a difference in distance between the annular recessed portion, which the force of the robot is applied, and a relevant slide portion for each operating freedom. This causes a difference in momentum due to resistance of the slide portion such that the robot&#39;s hand encounters a difficulty in a smooth movement in either direction of the operating freedom with a resultant extremely degraded positioning precision in such a direction of the operating freedom.  
           [0006]    Also, the hand of the change-over robot has no function to correct a relative positioning error caused during gripping operation of the hand and no function to detect that the annular recessed portion has been gripped. Consequently, even with the presence of displacement in position for some reasons such that the hand is unable to grip the annular recessed portion by any possibility, the change-over robot tends to carry out the regular operation, with a degraded reliability in operation of the vehicle body transfer machine.  
           [0007]    The present invention has been made with the above view and has an object to provide a vehicle body transfer machine and a method thereof which is able to change over a three-dimensional position of a locating pin in a smooth and reliable manner without the need for actuators such as air cylinders correlated in three axes of an operating freedom of the locating pin.  
           [0008]    According to one aspect of the present invention, there is provided a vehicle body transfer machine transferring a vehicle body along a transfer path by using a transfer truck with which the vehicle body is supported, the transfer truck being returned to an initial starting position of the transfer path for a repeated use when transfer of the vehicle body is terminated. The vehicle body transfer machine is provided with: a jig change-over stage located before the initial starting position of the transfer path; a plurality of locator jigs respectively mounted on the transfer truck in spaced relationship to each other, each of the plurality of locator jigs including an upwardly directed locating pin to position the vehicle body and having operating freedoms in orthogonal three axes involving horizontal two directions of X- and Y-directions and a vertical direction of a Z-direction to respectively alter a three-dimensional position of the locating pin, and a plurality of lock units being attached to each of the plurality of locator jigs to restrict the operating freedoms thereof so as to lock the locating pin at the three-dimensional position; an unlock-operating unit connected to the jig change-over stage to unlock-operate the plurality of lock units when the transfer truck is positioned in the jig change-over stage; and a jig change-over unit mounted on the jig change-over stage, the jig change-over unit being associated with corresponding one of the plurality of locator jigs to allow the operating freedoms thereof to be utilized for changing over the three-dimensional position of the locating pin of the corresponding one of the plurality of locator jigs to an arbitral three-dimensional position, while the unlock-operating unit being actuated to unlock-operate the plurality of lock units of the corresponding one of the plurality of locator jigs. The jig change-over unit includes a socket portion engageable with the locating pin of the corresponding one of the plurality of locator jigs, the socket portion being moveable toward the locating pin to be brought into engagement therewith under a first unlock condition established when the unlock-operating unit unlock-operates the plurality of lock units, which is correlated with the horizontal two directions, of the corresponding one of the plurality of locator jigs to perform a relative positioning in the two horizontal directions between the jig change-over unit and the corresponding one of the plurality of locator jigs.  
           [0009]    In other words, there is provided a vehicle body transfer machine transferring a vehicle body along a transfer path by using a transfer truck with which the vehicle body is supported, the transfer truck being returned to an initial starting position of the transfer path for a repeated use when transfer of the vehicle body is terminated. The vehicle body transfer machine is provided with: a jig change-over stage located before the initial starting position of the transfer path; a plurality of locator jigs respectively mounted on the transfer truck in spaced relationship to each other, each of the plurality of locator jigs including an upwardly directed locating pin to position the vehicle body and having operating freedoms in orthogonal three axes involving horizontal two directions of X- and Y-directions and a vertical direction of a Z-direction to respectively alter a three-dimensional position of the locating pin, and a plurality of lock units being attached to each of the plurality of locator jigs to restrict the operating freedoms thereof so as to lock the locating pin at the three-dimensional position; unlock-operating means for unlock-operating the plurality of lock units when the transfer truck is positioned in the jig change-over stage; and jig change-over means for changing over the three-dimensional position of the locating pin of corresponding one of the plurality of locator jigs to an arbitral three-dimensional position, while the unlock-operating means being actuated to unlock-operate the plurality of lock units of the corresponding one of the plurality of locator jigs. The jig change-over means includes socket means for engaging with the locating pin of the corresponding one of the plurality of locator jigs, the socket means being moveable toward the locating pin to be brought into engagement therewith under a unlock condition established when the unlock-operating means unlock-operates the plurality of lock units, which is correlated with the horizontal two directions, of the corresponding one of the plurality of locator jigs to perform a relative positioning in the two horizontal directions between the jig change-over means and the corresponding one of the plurality of locator jigs.  
           [0010]    Besides, there is provided a method transferring a vehicle body along a transfer path by using a transfer truck with which the vehicle body is supported, the transfer truck being returned to an initial starting position of the transfer path for a repeated use when transfer of the vehicle body is terminated. The method provides a jig change-over stage located before the initial starting position of the transfer path; provides a plurality of locator jigs respectively mounted on the transfer truck in spaced relationship to each other, each of the plurality of locator jigs including an upwardly directed locating pin to position the vehicle body and having operating freedoms in orthogonal three axes involving horizontal two directions of X- and Y-directions and a vertical direction of a Z-direction to respectively alter a three-dimensional position of the locating pin, and a plurality of lock units being attached to each of the plurality of locator jigs to restrict the operating freedoms thereof so as to lock the locating pin at the three-dimensional position; provides a jig change-over unit mounted on the jig change-over stage, the jig change-over unit being associated with corresponding one of the plurality of locator jigs to allow the operating freedoms thereof to be utilized for changing over the three-dimensional position of the locating pin of the corresponding one of the plurality of locator jigs; positions the transfer truck in the jig change-over stage; unlock-operates the plurality of lock units of each of the plurality of locator jigs when the transfer truck is positioned in the jig change-over stage; and changes over the three-dimensional position of the locating pin of each of the plurality of locator jigs to an arbitral three-dimensional position by using the jig change-over unit, while unlock-operating the plurality of lock units of each of the plurality of locator jigs. The jig change-over unit is moved toward the locating pin of the corresponding one of the plurality of locator jigs to be brought into engagement therewith under a unlock condition, which is established by unlock-operating the plurality of lock units, which is correlated with the horizontal two directions, of the corresponding one of the plurality of locator jigs to perform a relative positioning in the two horizontal directions between the of jig change-over unit and the corresponding one of the plurality of locator jigs.  
           [0011]    Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic plan view illustrating a vehicle body assembly line to which a vehicle body transfer machine of an embodiment according to the present embodiment is applied;  
         [0013]    [0013]FIG. 2 is a plan view of a transfer truck to be used by the vehicle body transfer machine shown in FIG. 1;  
         [0014]    [0014]FIG. 3 is a side view of the transfer truck shown in FIG. 2;  
         [0015]    [0015]FIG. 4 is an enlarged side view of the transfer truck shown in FIG. 3;  
         [0016]    [0016]FIG. 5 is a right side view, which is along an X-direction, of the transfer truck shown in FIG. 4;  
         [0017]    [0017]FIG. 6 is an enlarged view of a locating unit including a locating pin shown in FIGS. 4 and 5;  
         [0018]    [0018]FIG. 7 is a vertical cross sectional view of the locating unit shown in FIG. 6;  
         [0019]    [0019]FIG. 8 is a plan view of the locating unit shown in FIG. 7;  
         [0020]    [0020]FIG. 9 is an enlarged view of a clamp arm of the locating unit shown in FIG. 7;  
         [0021]    [0021]FIG. 10 is an enlarged view mainly illustrating a jig change-over stage of the vehicle body transfer machine shown in FIG. 1;  
         [0022]    [0022]FIG. 11 is an enlarged view mainly illustrating a jig change-over unit of the vehicle body transfer machine shown in FIG. 10; and  
         [0023]    [0023]FIG. 12 is a side view of the jig change-over unit shown in FIG. 11. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    To describe the present invention more in detail, a vehicle body transfer machine of an embodiment of the present invention to carry out a method of the present invention will be explained below with reference to the accompanied drawings.  
         [0025]    Referring to FIG. 1, there is shown a vehicle body assembly line, for vehicles such as automobiles, controlled by a controller C and arranged in a so-called mixed flow production system to which the vehicle body transfer machine of the present embodiment is applied. In FIG. 1, the vehicle body assembly line is constructed of a final welding line  1 , which is for a so-called floor main of a vehicle body, including a plurality of welding stages S 1 , S 2 , S 3  . . . Sn mainly composed of respective welding robots, a next preliminary welding line  2 , which is for a so-called body main of a vehicle body, including a plurality of welding stages S 11 , S 12 , S 13  . . . Sn mainly composed of respective welding robots, and left and right storage lines  3 ,  4  located at distal ends of the final welding line  1  and the preliminary welding line  2  to form a closed loop structure. A plurality of transfer trucks  5  are to be sequentially disposed in the final welding line  1 , the preliminary welding line  2 , and the left and right storage lines  3 ,  4  to move in a sequential transfer motion by means of transfer units, which are not shown, while carrying the body panel through the final welding line  1 , the storage line  3  and the preliminary welding line  2  for thereby increasing a completion quality of a vehicle body.  
         [0026]    Here, the final welding line  1  serves to carry out the final spot welding step at a large number of welding points on the body panel such as the floor main typically composed of an engine compartment, a front floor panel and a rear floor panel which have been preliminarily welded in its preliminary welding step, which is not shown, as to the floor main. Likewise, the next preliminary welding line  2  refers to a step for preliminary assembling a body panel such as the body main composed of left and right body sides, a roof panel and the pre-assembled floor main subsequent to the final welding step and for performing spot welding steps of these components to preliminary fix them to one another, that is, for preliminarily welding the body panel such as the body main.  
         [0027]    More specifically, after the transfer truck  5  is positioned at a panel supply stage Ss which serves as a starting distal section of the final welding line  1 , an overhead conveyor  6  transfers the preliminarily welded floor main, which is then to be supplied to the transfer truck  5 , by means of a drop lifter which is not shown, and the floor main is positioned on the transfer truck  5 . Then, the transfer truck  5  is moved along respective stages S 1 , S 2 , S 3  . . . Sn of the final welding line  1  to perform spot welding steps (final welding step) in a sequential manner. Upon termination of such spot welding steps, the transfer truck  5 , which carries the floor main, is transferred from the final welding line  1  to the storage line  3 .  
         [0028]    In the storage line  3 , the transfer truck  5  with the floor main is stored in a transversely storage manner and are soon transferred to the preliminary welding line  2  in a direction opposite to that in which the transfer truck  5  travels through the final welding line  1 . Then, during a course of traveling of the transfer truck  5  through the respective stages S 11 , S 12 , S 13  . . . Sm of the preliminary welding line  2 , the spot welding steps (preliminary welding step) are carried out for the body panel including the floor main and the left and right body sides or the like placed on the transfer truck  5 , sequentially. When the transfer truck  5 , which is loaded with the body main preliminarily welded by the completed preliminary welding step, is positioned at a panel carrying-out stage Se at a terminal section of the preliminary welding line  2 , a drop lifter, which is not sown, is allowed to lift up only the preliminarily welded body panel, that is, the body main which is then to be transferred to its next final welding step, which is not shown, by an overhead conveyor  7 .  
         [0029]    On the other hand, upon carrying out the vehicle body, an unloaded transfer truck  5  is transferred to the storage line  4  and kept in the transverse storage sate in a manner as previously described with reference to the storage line  3  such that the transfer truck  5  is soon returned to the initial starting section of the final welding line  1  for reuse.  
         [0030]    Here, the transfer truck  5  has a plurality of upright locator jigs with locating pins for supporting the body panel in a positioned relationship. The respective locator jigs are arranged to fully conform to the mixed flow manufacturing mode, that is, a three-dimensional position of each locating pins is enabled to be arbitrarily changed over or altered in order to have the respective locator jigs coped with the proper positioning and supporting of the body panels of a plurality of vehicle&#39;s models. Further, until the transfer truck  5  is transferred from the storage line  4  to the final welding line  1  to allow the body panel to be supplied at the panel supply stage Ss, respective positions of the locating pins must be preliminarily changed over to respective desired positions to achieve proper positioning and supporting of the body panel of another vehicle&#39;s model. To this end, a jig change-over stage Sj is preset at a preceding stage of the panel supply stage Ss. Incidentally, the jig change-over stage Sj is described below in detail.  
         [0031]    [0031]FIG. 2 is a plan view illustrating a detailed structure of the aforementioned transfer truck  5 , and FIG. 3 is a front view illustrating the same. As viewed in FIGS. 2 and 3, the transfer truck  5  includes a major part constructed of a base  8 , and also first and second rows, which are laterally spaced from one another, of locator jigs  9 A to  9 E and  10 A to  10 E which are longitudinally located to stand upright on the base  8  in a spaced relationship. Each of the locator jigs  9 A to  9 E and  10 A to  10 E is constructed of a major locator machine in the form of a manipulator or a robot with an operating freedom in orthogonal (perpendicular) three axes wherein a X-axis unit  16 , a Y-axis unit  24  and a Z-axis unit  30  of slide unit types are disposed without respective actuators and are so arranged as to allow the Z-axis unit to lie at the uppermost side. The major locator machine includes a locating unit  11  mounted at an upper distal end of the Z-axis unit  30  and composed of a locating pin  12  standing upright in a manner described below in detail. Further, each of the locator jigs  9 A to  9 E and  10 A to  10 E includes brake units serving as lock units, respectively, associated with orthogonal three axes of the operating freedom in a manner as will be described below in detail and has a function to allow the three orthogonal axes on the operating freedom to be restricted to cause the three-dimensional position of the aforementioned locating pin  12  to be firmly retained by itself. In addition, each locator jig also has a function to independently release the restricting force applied to each brake unit such that when the locating pin  12  responds to an external force exerted by the other unit, the three-dimensional position of the locating pin  12  is arbitrarily altered with the operating freedom in the orthogonal three-axes. Incidentally, in FIG. 3, a numeral F designates the floor main positioned by each locating pin  12 .  
         [0032]    Also, both distal ends of the base  8  are formed with positioning holes  13 ,  13  which are diagonally located at two points to provide positioning reference areas for carrying out the positioning of the transfer truck  5  at each stage with the jig change-over stage Sj.  
         [0033]    Among the plurality of locator jigs  9 A to  9 E and  10 A to  10 E, a typical example of a detailed structure of the locator jig  9 B is exemplarily described with reference to FIGS. 4 and 5, wherein FIG. 4 is an enlarged view of a major part of the structure shown in FIG. 3, and FIG. 5 is a right side view of the structure shown in FIG. 4.  
         [0034]    As viewed in FIGS.  2  to  5 , a pair of laterally spaced, X-axis guide rails  14 ,  14  are located on the base  8  for its entire length in a correlated relationship with the respective rows of the plurality of locator jigs  9 A to  9 E, and X-axis guide rails  115 ,  115  are similarly located with the respective rows of the plurality of locator jigs  10 A to  10 E.  10 A to  10 E. In each locator jig, an X-axis slider  17 , which forms a major body of the X-axis unit  16 , is located on the X-axis guide rails  14 ,  14  or the X-axis guide rails  115 ,  115  through a linear guide pair  15 ,  15  for sliding movement in a horizontal and an X-direction. A pair of laterally spaced brake shafts  18 ,  19  are located on the base  8  for its entire length in parallel relationship and are correlated with the respective rows of pluralities of locator jigs  9 A to  9 E and  10 A to  10 E, with a brake unit  20  being fixedly secured to an end of the X-axis slider  17 , which serves as a lock unit, and slidably coupled to corresponding one of the brake shafts  18  and  19 . The brake unit  20  mechanically locks the X-axis slider  17  at a given fixed position with a braking force to clamp and restrict its corresponding brake shaft  18  or brake shaft  19  by the action of a resilient member such as a coil spring and is operative to receive compressed air to instantaneously release the aforementioned braking force to provide the freedom of sliding movement to the X-axis slider  17 .  
         [0035]    As best seen in FIGS. 4 and 5 in which the locator jig  9 B is exemplarily described, a Y-axis base  21  is fixedly supported on the X-axis slider  17 , and a pair of Y-axis guide rails  22 ,  22  are fixedly supported on the Y-axis base  21  to lie perpendicular to the X-axis guide rail  14 . A Y-axis slider  25 , which forms a major body of the Y-axis unit  24 , is mounted to the Y-axis guide rails  22  through a linear guide pair  23  for sliding movement in a horizontal and a Y-direction. A brake shaft  26  is fixedly secured to the Y-axis base  21  for its entire length and extends in the Y-direction, with a brake unit  27  being coupled to the brake shaft  26  for sliding movement and fixedly secured to an end of the Y-axis slider  25  to serve as a lock unit thereof. The brake unit  27  is constructed in the entirely same structure as that of the X-axis unit  16  and mechanically locks the Y-axis slider  25  at a given fixed position with a braking force to clamp and restrict the brake shaft  26  by the action of a resilient member such as a coil spring while the brake unit  27  is operative to receive compressed air to instantaneously release the aforementioned braking force for thereby providing the freedom of sliding movement to the Y-axis slider  25 .  
         [0036]    A Z-axis base  29  is fixedly supported on the aforementioned Y-axis slider  25  through a bracket  28 . A Z-axis slider  31 , which forms a major body of the Z-axis unit  30 , is similarly mounted to the Z-axis base  29  through Z-axis guide rails and a linear guide pair for sliding movement in a vertical, i.e. a Z-direction. A brake shaft  33  is fixedly secured to the Z-axis base  29  for its entire length and extends in the Z-direction, with a brake unit  32  being connected to the brake shaft  33  for sliding movement and fixedly secured to the Z-axis slider  31  to serve as a lock unit thereof. The brake unit  32  is constructed in the entirely same structure as those of the X-axis unit  16  and the Y-axis unit  24  and mechanically locks the Z-axis slider  31  at a given height position with a braking force to clamp and restrict the brake shaft  33  while the brake unit  32  is operative to receive compressed air t to instantaneously release the aforementioned braking force for thereby providing the freedom of sliding movement to the Z-axis slider  31  in the vertical direction. An upper end of the Z-axis slider  31  is mounted with an upright locating unit  11 , which is mainly composed of the locating pin  12  with a clamping function in a manner as will be described below in detail, and a horizontally extending hook pin  34  (see FIGS. 11 and 12) in a close proximity relationship. Also, the hook pin  34  is supported at its both ends with a pair of brackets  35  as seen in FIG. 12.  
         [0037]    As clearly understood from the foregoing description, when a drive force is applied from outside, the locator jig  9 B has a function to arbitrarily enable the three-dimensional position of the location pin  12  to be altered in response to an associated movement of the X-axis unit  16 , the Y-axis unit  24  and the Z-axis unit  30 . Incidentally, the locator jig  9 B, which includes such a locating unit  11 , basically has the same structure as those of the other locator jigs  9 A,  9 C to  9 E and  10 A to  10 E.  
         [0038]    FIGS.  6  to  9  show a detailed structure of the locating unit  11  to be mounted to the distal end of each of the aforementioned locators  9 A to  9 E and  10 A to  10 E. The locating unit  11  is constructed of a hollow, cylindrical post section  37  with a mounting flange  36 , and a clamp cylinder  38 , composed of an air cylinder or a hydraulic cylinder type formed in a substantially rectangular column shape, which is fixedly coupled to the post section  37  through the mounting flange  36  thereof in a concentric relationship. The locating pin  12 , which has a tapered shape having its base portion formed with a seating flange  39 , is fixedly supported with an upper distal end of the post section  37  through a spacer  40  by means of a plurality of fixture bolts  41 .  
         [0039]    The clamp cylinder  38  includes a piston rod  45  and a clamp arm  43  associated with the same, which are held in a retracted state, i.e. a clamped condition, with the action of a compression spring (not shown) contained in the clamp cylinder  38  and which is operable only in response to compressed air or pressurized hydraulic pressure supplied from the outside to lift the piston rod  45  to render the clamp cylinder  38  be brought into an unclamped condition.  
         [0040]    The locating pin  12  is partly formed with a vertically extending slit-shaped recess  42  in communication with an internal space of the post section  37  to allow the clamp arm  43  formed in a substantially key-shape as seen in FIG. 9, which serves as a clamping unit, to be inserted for a locking and unlocking movement. In particular, an upper distal end of the key-shape of the clamp arm  43  is exposed to the outside of an opening portion  44  formed at the base portion of the locating pin  12 , with a lower distal end of the clamp arm  43  being coupled to the piston rod  45  of the clamp cylinder  38 . The clamp arm  43  is formed at its intermediate portion with an angled grooved cam  46  with which a fixed pin  47 , laterally extending in a radial direction of the post section  37 , engages. With such a structure, upon extending or retracting movements of the clamp cylinder  38 , the clamp arm  43  is brought into an clamping operation or an unclamped operation between a clamping position C 1  and an unclamped position C 2 . Especially under the clamped condition shown in FIG. 7, a lower panel W 3 , which is a part of a given panel such as the floor main F, is clamped in a pinched state with the distal end of the clamp arm  43  and the seating flange  39 .  
         [0041]    As viewed in FIG. 7, the panel W 3  of the floor main F has a downwardly protruding embossed portion E formed with a location bore R, with the locating pin  12  mating with the location bore R to allow a circumferential periphery of the location bore R to be seated on the seating flange  39  of the locating pin  12  for thereby finally finishing the positioning step of the locating pin  12 .  
         [0042]    Inside the post section  37  of the locating unit  11 , a shaft  48  of a stepped diametrical shape is located for sliding movement in parallel to an axis of the locating pin  12  and is urged upward as seen in FIG. 7 by a compressed coil spring  49 . A coupling plate  50  is connected to a small diameter end portion of the shaft  48  and has an end portion, which is offset from the shaft  48 , fitted with a lower distal end of a detection pin  51 , standing upright in parallel to the shaft  48 , which protrudes from or retracts from a work-piece seating surface  39   a  of the seating flange  39  of the locating pin  12 . With such a structure, an upper distal end of the detection pin  51  remains protruded from the seating flange  39  in the absence of the panel W 3  on the seating flange  39 . However, in the presence of the given panel W 3  seated on the seating flange  39 , the distal end of the detection pin  51  is retracted within the seating flange  39  to cause the shaft  48  to move downward.  
         [0043]    Further, a proximity switch  52  is located on the post section  37  at a position opposed to a lower distal end of a large diameter section of the shaft  48  such that when the detection pin  51  protrudes from the seating flange  39  as viewed in FIG. 7 to cause the lower distal end of the shaft  48  is separated from the proximity switch  52  which remains OFF state. Upon retracting movement of the detection pin  51  into the seating flange  39  as described above, the proximity switch  52  is turned on to ON state by sensing the proximity approach of the shaft  48  due to its downward sliding movement.  
         [0044]    Thus, a work-piece seating detection mechanism  53  serving as a work-piece seating detection means is constructed of the shaft  48 , the detection pin  51  and the proximity switch  52  to detect the presence of or the absence of the panel W 3  with respect to the seating flange  39 . With this arrangement, sliding displacements of the detection pin  51  and the shaft  48  following the seating phase of the panel W 3  on the seating flange  39  cause the presence or the absence of the panel W 3  to be detected with the proximity switch  52  for turning ON or OFF. Incidentally, in such a work-piece seating detecting mechanism, a photoelectric sensor may be applied to detect the presence of the panel W 3 , and compressed air may be used to urge the locating pin  12 . Also, a work-piece seating detection mechanism of a non-contact type may be alternatively employed.  
         [0045]    [0045]FIG. 10 shows a detailed structure of the jig change-over stage Sj shown in FIG. 1. The jig change-over stage Sj has a laterally space, upright standing posts  62 , to which the transfer truck  5  is transferred with a transfer unit  61  of a plane shuttle type and is positioned in a horizontal condition with a reference to the positioning bores  13 ,  13  (see FIG. 2). The jig change-over stage Sj also includes a machine frame  63  composed of a pair of laterally spaced, vertical frame components  63   a ,  63   a  standing upright from a base frame component  63   b  to remain outward of the posts  62 ,  62 , and a top frame component  63   c  connected to upper distal ends of the vertical frame components  63   a ,  63   a  such that the machine frame  63  stands straddling the transfer truck  5  which remains in a positioned condition. The top frame component  63   c  carries the same number of jig change-over units  64  as those of the locator jigs  9 A to  9 E and  10 A to  10 E mounted on the transfer truck  5  (provided that the structure shown in FIG. 10 corresponds to that shown in the right side view of FIG. 4, wile one piece of jig change-over unit  64  and associated locator jig  9 B being mainly illustrated in FIG. 10). That is, the independent jig change-over units  64  are prepared for respective locator jigs  9 A to  9 E and  10 A to  10 E to enable the positions of the locating pins  12  to be changed over at the respective locating jigs  9 A to  9 E and  10 A to  10 E. Incidentally, a single jig change-over unit or some jig change-over units less than the locator jigs  9 A to  9 E and  10 A to  10 E may be prepared, provided that such a single jig change-over is sequentially applied to the locator jig or such some jig change-over units are correspondingly shared by the locator jigs.  
         [0046]    As viewed in FIGS. 11 and 12, the jig change-over unit  64  is constructed of a mother machine including the X-axis unit  65 , the Y-axis unit  66  and Z-axis unit  67 , of respective ball-screw types driven by NC motors, which are assembled such that the Z-axis unit  67  remains in the lowest position to form a manipulator or a robot with the operating freedom in the three orthogonal axes. A distal end of the Z-axis unit  67  of the mother machine has a socket portion  68  and a swing arm  69  which serves as a coupling member, with an autonomous operation of the mother machine enabling the three dimensional positions of the socket portion  68  and the swing arm  69  to be altered to respective arbitrary positions.  
         [0047]    In particular, the X-axis unit  65  includes a X-axis base  72 , suspended from the top frame component  63   c , in which a screw shaft  71  of a ball-screw type is incorporated, a X-axis drive motor  70  supported on the X-axis base  72  to drive the screw shaft  71 , and a X-axis slider  73  guided by the X-axis base  72  and connected to the screw shaft  71  for sliding movement in the lateral X-direction. The Y-axis unit  66  includes a Y-axis base  76 , fixedly mounted to the X-axis slider  73  by means of a flange  78 , in which a screw shaft  75  of a ball-screw type is incorporated, a Y-axis drive motor  74  supported on the Y-axis base  76  to drive the screw shaft  75 , and a Y-axis slider  77  guided by the Y-axis base  76  and connected to the screw shaft  75  for sliding movement in the lateral Y-direction. The Z-axis unit  67  includes a Z-axis base  81 , fixedly mounted to the Y-axis slider  77  by means of a flange  82 , in which a screw shaft  80  of a ball-screw type is incorporated, a Z-axis drive motor  79  supported on the Z-axis base  81  to drive the screw shaft  80 , and a Z-axis slider  83  guided by the Z-axis base  81  and connected to the screw shaft  80  for sliding movement in the vertical Z-direction. An upper distal end of an extension  84  is fixedly secured to a lower end of the Z-axis slider  83 , and a lower distal end of the extension  84  is mounted with the socket portion  68  and the swing arm  69  serving as the coupling member. With such a structure, the jig change-over unit  64  enables the X-axis unit  65 , the Y-axis unit  66  and the Z-axis unit  67  to corporate with one another to allow the three dimensional positions of the socket portion  68  and the swing arm  69  to be arbitrarily altered.  
         [0048]    The socket portion  68  is directly secured to a bottom end of the extension  84  by welding and has a simple cylindrical configuration to mate with the locating pin  12  of the locator jig  9 B of the transfer truck  5  which remains in the positioned condition at the jig change-over stage Sj as previously noted above. The presence of a clearance between the socket portion  68  and the locating pin  12  provides an adverse affect on the positioning precision of the locating pin  12  itself and, therefore, the clearance between the socket portion  68  and the locating pin  12  in a mating stage is preset to a relatively and strictly designed value.  
         [0049]    As best seen in FIG. 11, further, the swing arm  69 , which serves as the coupling member, is supported with the extension  84  through brackets  85  and a hinge pin  86  fixedly supported with the brackets  85  for swinging movement. A lower distal end of the swing arm  69  is formed with an engagement recess  87  and an upper distal end of the swing arm  69  is connected to a piston rod  89  of an air cylinder  88  of a trunnion type which serves as a drive source. With such a structure, the swing arm  69  is enabled to move the swing arm  69  for swinging movement between a coupling position P 1  and an uncoupling position P 2  in response to compressing and retracting movements of the air cylinder  88 . That is, the swinging movement of the swinging arm  69  from the uncoupling position P 2  to the coupling position P 1  allows the socket portion  60  to initially mate with the locating pin  12  at all times under a condition wherein the relative positioning is performed between the jig change-over unit  64  and the locator jig  9 B. Accordingly, during swinging movement of the swing arm  69  toward the coupling position P 1 , the engagement recess  87  of the swing arm  69  approaches the hook pin  34  of the locator jig  9 B to be brought into engagement with the hook pin  34  as viewed in FIG. 11.  
         [0050]    Now, the operation of the vehicle body transfer machine as the above constructed will be described below in detail. Incidentally, such an operation is carried out by the controller C.  
         [0051]    When the transfer truck  5 , which has completed the transfer of the vehicle body of a particular vehicle&#39;s model type shown in FIGS. 1 and 10, is rendered to remain in the storage line  4  at once and is subsequently positioned at the jig change-over stage Sj shown in FIGS. 1 and 10 for the transfer of the vehicle body of another vehicle&#39;s model, the locator jigs  9 A to  9 E and  10 A to  10 E of the transfer truck  5  are mutually brought into opposed relationships with the respective jig change-over units  64 , carrying out the change-over of the respective jigs to alter the positions of the locating pins  12  at respective positions necessary for positioning and supporting the vehicle body of another vehicle&#39;s model.  
         [0052]    Concurrently, a pressurized supply unit  100  (see FIG. 1) and an electric power supply unit  110  (see FIG. 1), which are preliminarily prepared at the jig change-over stage Sj, are actuated to allow joint members of a plurality of connection lines for supplying pressurized air and joint members for supplying electric power to be associated with joint members mounted to the transfer truck  5 . This results in supply of electric power and supply of compressed air to be performed at desired areas. Thus, it will be seen that the pressurized air unit  100  serves as an unlock-operating unit for releasing the braking forces of the brake units  20 ,  27 ,  32  mounted to the respective locator jigs  9 A to  9 E and  10 A to  10 E. Also, these movements are similarly obtained in the respective stages of the floor main final welding line  1  and the body main preliminary welding line  2  except for the jig change-over stage Sj.  
         [0053]    When the transfer truck  5  is positioned at the jig change-over stage Sj in a manner as described above, an unlock-operating command signal is delivered from the controller C and compressed air is supplied to the brake units  20 ,  27 , associated with the operating freedoms in the horizontal two directions, i.e. X-direction and Y-direction, among the plurality of brake units  20 ,  27 ,  32 , serving as the respective locking units, which are independent for respective operating freedoms of the locator jigs  9 A to  9 E and  10 A to  10 E as seen in FIGS. 4 and 5, while quickly releasing the braking forces of the brake units  20 ,  27  (into an unlocked condition). When this occurs, the restricted conditions of the respective locator jigs  9 A to  9 E and  10 A to  10 E, which has the operating freedoms in the orthogonal three axes in the X-, Y- and Z-directions, are released in the horizontal X- and Y-directions such that application of external forces to the respective locating pins  12  enables the locating pins  12  to be moved in a free condition at least in the horizontal plane.  
         [0054]    At the same time, compressed air is also supplied to the clamp cylinder  38  of the locator unit  11  shown in FIG. 7, rendering the clamp arm  43  to be retained in the unclamped condition to lift up the clamp arm  43 .  
         [0055]    Incidentally, the controller C stores information about the vehicle body of the particular vehicle&#39;s model which has been previously positioned and supported with the transfer truck  5  which is supported and positioned at the aforementioned jig change-over stage Sj, i.e. information about current three dimensional positions of the respective locating pins  12  of the locator jigs  9 A to  9 E and  10 A to  10 E. Concurrently, the controller C stores information of a vehicle body of a particular vehicle&#39;s model to be subsequently supported with the aforementioned transfer truck  5 , i.e. information about the three dimensional positions of the respective locating pins  12  required for positioning and supporting the vehicle body to be subsequently processed.  
         [0056]    Upon receipt of a command signal from the controller C, as seen in FIGS. 11 and 12, the jig change-over units  64  are activated in the autonomous operation with the operating freedom in the orthogonal three axes to cause the socket portions  68  to be moved in axial alignment with the respective locating pins  12  and then lowered to allow the socket portions  68  to be mated with relevant locating pins  12 . When this takes place, even when the locating pin  12  has an error in a relative position on a plane with respect to the relevant socket portion  68 , the presence of a tapered shape of the locating pin  12  allows the locating pin  12  to engage with the socket portion  68  due to its autonomous function. Thus, the position of the locating pin  12  is corrected within the plane in the X- and Y-directions of the locating pin  12  so as to follow the socket portion  68  such that both are completely aligned in positioning the horizontal plane.  
         [0057]    Simultaneously, effectively utilizing the work-piece seating detection mechanism  53  shown in FIG. 7 enables confirmation of the presence of the socket portion  68  being seated in the proper place. If, in this instance, the socket portion  68  has seated on the seating flange  39  of the locating pin  12  in place of the panel W 3  as shown in FIG. 7 and FIGS. 11 and 12, then, the work-piece seating detection mechanism  53  is actuated. In such a manner, if the locating pin  12  does not detect the seating of the socket portion  68  by any possibility, the work-piece seating detection mechanism  53  generates a given alarm to stop a subsequent processing step for a while.  
         [0058]    Consecutively, under a condition wherein the aforementioned work-piece seating detection mechanism  53  is actuated, as seen in FIGS. 11 and 12, the swing arm  69  of the jig change-over unit  64 , which is located independently of the aforementioned socket  68 , is operated to cause the swing arm  69  to swing from the uncoupled position P 2  toward the coupling position P 1 . Thus, the swing arm  69  is brought into engagement with the hook pin  34 , adjacent the locating pin  12 , from the lateral side such that the jig change-over units  64  are mechanically and individually coupled with the locator jigs  9 A to  9 E and  10 A to  10 E. When this occurs, since the presence of the previous engagement between the socket portion  68  and the locating pin  12  allows the jig change-over units  64  to be positioned in the horizontal plane with respect to the locator jigs  9 A to  9 E and  10 A to  10 E while the operating freedoms, in the vertical direction (Z-direction), of the locator jigs  9 A to  9 E and  10 A to  10 E remain in the restricted condition with the brake unit  32 , the jig change-over units  64  and the locator jigs  9 A to  9 E and  10 A to  10 E are mechanically coupled with one another in a smooth and reliable manner.  
         [0059]    Upon receipt of a next unlock-operating command subsequent to the mechanical coupling between the jig change-over units  64  and the locator jigs  9 A to  9 E and  10 A to  10 E, compressed air is supplied to only the brake unit  32  correlated with the operating freedom in the Z-direction (vertical direction) among the plurality of brake units  20 ,  27 ,  32 , which serve as the lock unit, located independently for respective operating freedoms of the locator jigs  9 A to  9 E and  10 A to  10 E. Thus, the brake force of the brake unit  32  is immediately released (in the unlocked condition). This causes the restricted conditions in the X-axis and Y-axis as well as the vertical direction of the respective locator jigs  9 A to  9 E and  10 A to  10 E with the orthogonal three axes of operating freedoms in the X-, Y- and Z-directions to be released. When this takes place, applying an external force to the locating pin  12  and the swing arm  69  enables the locating pin  12  to be freely moved in any direction among the X-, Y- and Z-directions.  
         [0060]    Under the above state, the locator jigs  9 A to  9 E and  10 A to  10 E are lowered to the lowest position, in the Z-direction at once with the autonomous operation of the jig change-over unit  64 , at which the locating pin  12  is moved in the horizontal plane in the X- and Y-direction with the autonomous operation of the jig change-over unit  64 , thereby enabling the locating pin  12  to be located at a position required for properly positioning and supporting the vehicle body of the subsequent vehicle&#39;s model. In this instance, also, the controller C delivers positioning information of the locating pin  12 , necessary for initiating the positioning of the vehicle body of the subsequent vehicle&#39;s model, to the jig change-over unit  64 .  
         [0061]    In such a manner, moving the locating pin  12  at the lowest position using the orthogonal three axes in the operating freedoms of the locator jigs  9 A to  9 E and  10 A to  10 E precludes the slide portions of the locator jigs  9 A to  9 E and  10 A to  10 E having the operating freedoms in the X- and Y-direction from being applied with an excessive force to perform change-over of the position of the locating pin  12  with an extremely small operating power in a more smooth manner. Further, when the position of the locating pin  12  in the horizontal plane in the X- and Y-direction is determined, the supply of compressed air to the brake units  20 ,  27  correlated in the X-and Y-direction among the brake units  20 ,  27 ,  32 , which are independent for each operating freedom of the locator jigs  9 A to  9 E and  10 A to  10 E is interrupted to be brought into the braking, restricted condition again. As such, the locating pin  12  is positioned and restricted in a proper position in conjunction with the X- and Y-direction.  
         [0062]    In a consecutive step, the autonomous operation of the jig change-over unit  64  allows the locator jigs  9 A to  9 E and  10 A to  10 E to be raised such that the locating pin  12  is positioned to a height position (in the Z-direction) required for positioning and supporting the vehicle body of the subsequent vehicle&#39;s model until the positioning operation is completed. When this occurs, the brake unit  32  related in the Z-direction is brought into the braked and restricted condition to cause the locating pin  12  to be positioned in the restricted state. Thus, the locating pins  12  of the respective locator jigs  9 A to  9 E and  10 A to  10 E are changed over in the three dimensional position required for positioning and supporting the vehicle body of the subsequent vehicle&#39;s model.  
         [0063]    In addition, returning the swing arm  69  from the coupling position P 1  to the uncoupled position P 2  with the autonomous operation of the change-over unit  64  while releasing the mechanical coupling between the locator jigs  9 A to  9 E and  10 A to  10 E allows the socket portion  68  to be removed from the relevant locating pin  12  and moved into the original starting position.  
         [0064]    With the aforementioned positioning steps, the change-over operations of the jigs are completed at the jig change-over stage Sj while uncoupling the joint members of the compressed air supply unit  100  and the electric power supply unit  110  in the transfer truck  5 . Thereafter, the transfer truck is transferred to the panel supply stage Ss, i.e. the starting end section of the floor main multiple striking line as seen in FIG. 1, whereas the jig change-over stage Sj is supplied with the subsequent transfer truck  5  with the following sequential steps being repeatedly implemented in the same manner as discussed above.  
         [0065]    By the above described structure, an important advantage of the vehicle body transfer machine of the present embodiment concerns a capability of changing the two-dimensional position of the locating pin within a horizontal plane first and subsequently changing the position of the locating pin in the height direction without causing the locating pin to be moved in the three-dimensional direction at one operation. Thus, no air cylinder, that would otherwise required in the related art practice, is required for restoring the locating pin at the original positions independent from one another with the operating freedom in the three axes. This results in a simplified structure. Also, since no excessive force is applied to the sliding portions associated with the operating freedom in orthogonal three axes, it is possible for the locating pin to be shifted in an extremely smooth and reliable manner, with a resultant remarkable improvement over the positioning precision of the locating pin.  
         [0066]    Also, another advantage of the vehicle body transfer machine of the present embodiment concerns a capability of moving the socket portion in a direction to be brought into engagement with the locating pin after rendering the lock units, associated with two horizontal directions involving the X- and Y-directions, to be unlocked such that, even with the presence of an error in the relative position between the socket portion and the locating pin, the error in the relative position is corrected through a self-centering function to obtain a reliable engagement of these components with a resultant increase in the operating reliability of the machine.  
         [0067]    Also, another advantage of the vehicle body transfer machine of the present embodiment concerns a capability of moving the locating pin in the horizontal plane in the X- and Y-directions after lowering the locator jig to its lowermost position whereby no excessive force is exerted to the sliding portions enabling the operating freedom to allow the locating pin to move in a remarkably smooth and stable manner for thereby significantly improving the positioning precision of the locating pin.  
         [0068]    Also, another advantage of the vehicle body transfer machine of the present embodiment concerns a capability of changing over the position of the locating pin in the vertical direction after the change-over of the position of the locating pin in the horizontal two directions, i.e. the X- and Y-directions has been completed and thereafter the lock units associated with the horizontal two directions have been brought into locked state again whereby when changing over the position of the locating pin in the vertical direction, no displacement is encountered in the position of the locating pin in the X- and Y-directions with a resultant improvement in positioning precision of the locating pin.  
         [0069]    Also, another advantage of the vehicle body transfer machine of the present embodiment concerns the presence of the work-piece seating detection unit, located at the work-piece seating surface of the locating pin, which allows a substantially regional area of the locating pin to have the positioning function as well as the seating state detecting function. Consequently, the presence of preliminarily standardized size in the locating pins and the locating bores allows the locating pin and the work-piece seating detection unit to be used commonly for the body panels of plural vehicle&#39;s models which are different from one another to provide an highly improved general-purpose property.  
         [0070]    Also, another advantage of the vehicle body transfer machine of the present embodiment concerns the work-piece seating detection unit which also functions as a detecting unit for detecting a completed engagement between the socket portion and the relevant locating pin, with the completed engagement between these components being confirmed for every engagement step to highly improve an operating reliability.  
         [0071]    Also, another advantage of the vehicle body transfer machine of the present embodiment concerns the work-piece seating detection unit which enables a mechanical detection of the presence of a seated condition of the work-piece using the detection pin adapted to protrude or retract depending on seating or unseating of the body panel or the socket portion for enabling a reliable detection of the seating condition of the work-piece to provide an improved reliability in the work-piece seating detection property.  
         [0072]    And also, another advantage of the vehicle body transfer machine of the present embodiment concerns the presence of the clamp unit internally located in the locating pin for clamping the vehicle body panel to allow the locating pin to intensively have the locating-pin function, the work-piece seating detecting function and the panel claming function in one piece with a resultant further miniaturized structure in the locating pin with a reduced space thereof.  
         [0073]    The entire content of a Patent Application No. TOKUGAN 2001-068039 with a filing date of Mar. 12, 2001 in Japan is hereby incorporated by reference.  
         [0074]    Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art, in light of the teachings. The scope of the invention is defined with reference to the following claims.