Abstract:
An assembly line, wherein at least one operating branch of fixed length accommodates a number of platforms aligned with one another and with a given travelling direction; each platform being designed to receive a respective vehicle body, feed it in the travelling direction, and subject it to a succession of  n  assembly operations along the operating branch; each platform being designed for connection to at least one longitudinal extension to assume a total length, which depends on the length of the body carried, and ranges between a minimum length equal to the length of the platform with no extension, and a maximum length; and the length of the operating branch being equal to  n  times the maximum length.

Description:
The present invention relates to a motor vehicle assembly line. 
     BACKGROUND OF THE INVENTION 
     Currently used motor vehicle assembly lines comprise a succession of moving platforms, each for transporting a vehicle body along an assembly path, and of a length depending on the length of the body. 
     Assembly lines of this sort are designed to transport a specific type of body, and have to be completely restructured to switch from one body type to another. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a versatile assembly line, i.e. adaptable cheaply and easily to different types of vehicle bodies. 
     According to the present invention, there is provided a motor vehicle assembly line as claimed in the accompanying Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a schematic layout of a preferred embodiment of the assembly line according to the present invention; 
         FIG. 2  shows a larger-scale view in perspective of a detail in  FIG. 1 ; 
         FIG. 3  shows the same view as in  FIG. 2 , of a variation of the  FIG. 2  detail; 
         FIG. 4  shows a side view of the  FIG. 3  detail; 
         FIG. 5  shows the same view as in  FIG. 2 , of a further variation of the  FIG. 2  detail. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in  FIG. 1  indicates as a whole a motor vehicle assembly line. 
     Line  1  is an endless line comprising two U-shaped portions  2  and  3 , which are located at different levels, portion  2  lower than portion  3 , and overlap as described below (for the sake of clarity, portion  3  is shown coplanar with and alongside portion  2  in  FIG. 1 ). 
     Portion  2  comprises an input branch  4 , an output branch  5 , and a transfer branch  6  connecting the output of input branch  4  to the input of output branch  5 . Input branch  4  and output branch  5  are the same length L, and each comprise a conveyor  7  for a number of platforms  8  contacting end to end and each of which supports a motor vehicle body  9  and is of a length S depending on the length of relative body  9 . 
     As shown in  FIG. 2 , each conveyor  7  is housed inside a pit  10  formed in a floor  11 , and comprises two rails  12  parallel to a travelling direction  13  and supported in a fixed position on supporting blocks  14 . 
     As shown in  FIG. 3 , each platform  8  comprises a frame  15  supported on rails  12  with the interposition of a number of trolleys, and in turn comprising two outer longitudinal members  16  and a number of intermediate longitudinal members  17  connected by two end cross members  18  and a number of intermediate cross members  19 . Each end of each longitudinal member  17  projects from the relative end cross member  18 , and is fitted with a plate  20  for the purpose described below. 
     Each platform  8  also comprises a normally wooden floor  21 , which covers the rectangular grid defined by frame  15 , and defines a walk-on surface coplanar with floor  11  ( FIG. 2 ). Finally, each platform  8  also comprises a known electromechanical lift table  22 , which is fitted to the centre of frame  15 , through an opening in floor  21 , supports a respective body  9 , and is connected in known manner to an electric power supply mains (not shown) by sliding contacts or induction (not shown) on frame  15 . 
     Input branch  4  and output branch  5  are each equipped in known manner (not shown) with a device for moving platforms  8 , contacting end to end, forward, and which comprises, in known manner not shown, a friction push device located at the input of relative input branch  4 , output branch  5 , and cooperating frictionally with the outer lateral surfaces of longitudinal members  16 ; and a friction brake device located at the output of relative input branch  4 , output branch  5 , and which frictionally engages the outer lateral surfaces of longitudinal members  16 , and cooperates in known manner with the friction push device to move platforms  8 , contacting end to end, in travelling direction  13  at a given constant speed V. 
     As shown in  FIG. 1 , a receiving branch  23  and a pickup branch  24  are connected in-line to the input and output respectively of each of input and output branches  4  and  5 . 
     More specifically, receiving branch  23  of input branch  4  receives platforms  8  at zero linear speed from an elevator  25 , accelerates them to a speed V 1 , and then decelerates them to a speed V 2  (V 1 &gt;V 2 ) approximating but no less than the travelling speed V of platforms  8  along input branch  4 . And pickup branch  24  of input branch  4  receives platforms  8  at the travelling speed V of platforms  8  along input branch  4 , accelerates them to speed V 1 , and then decelerates them to zero linear speed for loading onto an input turntable  26  of transfer branch  6 . 
     Receiving branch  23  of output branch  5  receives platforms  8  at zero linear speed from an output turntable  27  of transfer branch  6 , accelerates them to speed V 1 , and then decelerates them to a speed V 2  (V 1 &gt;V 2 ) approximating but no less than the travelling speed V of platforms  8  along output branch.  5 . And pickup branch  24  of output branch  5  receives platforms  8  at speed V, accelerates them to speed V 1 , and then decelerates then to zero linear speed at an elevator  28 . 
     Elevator  28  connects the output of portion  2  to the input of portion  3 , and elevator  25  connects the output of portion  3  to the input of portion  2 . 
     From elevator  28 , portion  3  comprises an input branch  29  and an output branch  30  connected by a transfer branch  31 . Input branch  29  extends through an unloading station for unloading the assembled bodies  9  off respective platforms  8 , and between elevator  28  and an input turntable  33  of transfer branch  31 ; and output branch  30  extends through a loading station  34  for loading the unassembled bodies  9  onto respective platforms  8 , and between an output turntable  35  of transfer branch  31  and elevator  25 . 
     With reference to  FIGS. 3 and 4 , the length P of each platform  8  is adjustable to the length of body  9  by fitting platform  8  with one or two end extensions  36 , each comprising a frame  37  covered with a floor (not shown) similar to and coplanar with floor  21 . Frame  37  is the same width as frame  15 , and comprises two cross members  38 , the corresponding ends of which are connected by two outer longitudinal members  39  spaced the same distance apart as longitudinal members  16 ; and the intermediate portions of cross members  38  are connected by a number of intermediate longitudinal members  40 , of length E, which are fitted on each end with a plate  41  similar to plates  20 , and are spaced the same distance apart between longitudinal members  39  as longitudinal members  17  between longitudinal members  16 . 
     Each platform  8  of length:
 
S=Smin=P
 
is extended to form a composite platform  8  of a total length S:
 
 S=S int= P+E  or  S=S max= P +2 E  
 
by positioning frame  37  of (or of each) extension  36  coplanar with frame  15 , with longitudinal members  39  aligned with respective longitudinal members  16 , with longitudinal members  40  aligned with respective longitudinal members  17 , and with plates  41  (the ones facing frame  15 ) positioned contacting respective plates  20 ; and by connecting each two contacting plates  41  and  20 , using screws and/or through bolts and/or any other removable fast-fit connecting devices, to fit extension  36 , or each extension  36 , to and projecting from frame  15  of platform  8  to form a respective composite platform  8 .
 
     In the example shown, platforms  8  along both input and output branches  4  and  5  are arranged contacting end to end and have all the same length S, and the length L of each of input and output branches  4  and  5  is calculated as follows:
 
 L= n ·S max;  L≅ m ·S min;  L≅ r ·S int
 
where:
 
   m =L/S min&gt; n  r =L/S int&gt;   n &lt; m   
 
and where, hereinafter and in the Claims:
           n  is intended to represent the number of assembly operations to be performed along each of input and output branches  4  and  5 , and   the term ‘assembly operation’ is intended to mean all the operations performed on the body as respective platform  8  moves forward by a distance equal to the length of platform  8 .       

     When using platforms  8  of length Smin or Sint, there will therefore be, at the end of each of input and output branches  4  and  5 , a certain number of platforms  8  ( m - n or  r - n ) not used to perform any assembly operations on respective bodies  9 . 
     In actual use, after fitting line  1  with platforms  8  of the right length to support bodies  9  for assembly, all the branches of line  1  are set in motion. In particular, input and output branches  4  and  5  are set in motion at a given constant speed compatible with the work to be carried out. 
     Platforms  8  are loaded with respective bodies  9  at loading station  34 ; after which, each platform  8  loaded with respective body  9  is fed to elevator  25 , which lowers it to the level of the input of receiving branch  23 , which feeds it onto input branch  4 . 
     Platforms  8 , contacting end to end, travel along input branch  4 , are transferred by transfer branch  6  to the input of output branch  5 , and, contacting end to end, travel up to pickup branch  24  and elevator  28 , which raises them successively to the level of input branch  29 . 
     At this point, platforms  8  are fed to unloading station  32 , where the finished bodies  9  are unloaded off respective platforms  8 ; and platforms  8  are fed back along transfer branch  31  to loading station  34  to receive further bodies  9  for assembly. 
     As will be clear from the above description :
         line  1  provides for assembling bodies  9  of different lengths; and   the working space occupied along each of input and output branches  4  and  5  varies in proportion to the length of bodies  9  being assembled, thus minimizing operator movement.       

     Obviously, in a variation not shown, input and output branches  4  and  5  may be arranged in-line by eliminating transfer branch  6 , pickup branch  24  of input branch  4  and receiving branch  23  of output branch  5 , and by modifying portion  3  of line  1  accordingly. In which case, a return line must obviously be provided to return the empty platforms  8  from unloading station  32  to loading station  34 . 
     In a variation not shown, extensions  36  are mounted on platforms  8 , and are connected to and extractable from frames  15  telescopically.