Abstract:
A plant for welding automotive vehicle bodies that are conveyed in succession in an assembly line to a single processing station having equipment for positioning, holding and welding different types of automotive bodies, a pair of opposed stationary frames pivotally supporting elongate members, which in turn rotatably support tool supporting units, each of which carries a plurality of tool assemblies. The elongate members pivot normal to the assembly line path to place the tool supporting units in and out of operating position; and the tool assemblies are revolvable about the rotatable tool supporting units to select one of the tool assemblies for a particular vehicle body type.

Description:
This application is a continuation of application Ser. No. 374,070 filed June 30, 1989, now abandoned. 
    
    
     DESCRIPTION 
     The present invention relates to an improved plant for performing a welding operation commmonly called &#34;tacking&#34;, of automotive bodies in a single processing station, comprising a pair of opposed stationary units on which the tools required for the work are mounted in a revolving manner. 
     As is well known to those skilled in the sector of automatic plants for the assembly and welding of shaped metal sheets and similar details in monolithic structures, such as, for example automotive vehicle bodies, truck cabs and the like; elements called &#34;configurators&#34; which consist of a frame supporting centering means and holding clamps, and optionally welding clamps, arranged in such a manner as to hold and weld a particular configuration of sheet metal have already been proposed. Given their peculiar function the configurators must be actuated especially for a specific product, since the holding and welding clamps must be designed and arranged appropriately. 
     To make the processing stations of the production line flexible the configurators do not form a single block with the processing station, but can be disengaged therefrom and substituted to adapt a given processing station to different products, e.g. when processing different models of automotive vehicle bodies. 
     Such a plant is described for example in German Pat. No. 2810822. 
     In seeking to make the plant still more flexible there have been provided, as described for example in Italian Pat. No. 20226 A/84 filed 26 Mar. 1984, Pat. No. 23102 A/82 filed 2 Sept. 1982, and Pat. No. 23055 A/83 filed 29 Sept. 1983, all in the name of Gaetano Di Rosa and Italian patent application No. 67563 A/77 in the name of Weldesign di Nepote Andre &amp; C. s.a.s., processing stations comprising a handling system for said configurators designed to automatically replace the configurators by withdrawing them from a stock of configurators and positioning them automatically in their working position in the processing station. This makes possible the alternation, on the production line, of different models each of which is associated, a particular pair of configurators. The processing requires in general, a configurator for each side of the line. 
     Although the system proposed for storage of the configurators, the number of said configurators and the method of moving them to the position provided in the processing station are different in each of the above mentioned patents, said systems suffer in general from a serious and fundamental shortcoming due to their structural complexity, and the space they occupy particularly storage space. 
     In such known systems handling of the configurators also requires a rather long time. 
     In addition, the configurator conveyance and alternation system is rather complex since it has to be sized for accurate handling of the large, heavy loads represented by the configurators; and this adds considerably to the cost of building and maintaining it. 
     The general object of the present invention is to obviate the above mentioned shortcomings by providing an automatic plant for the assembly of shaped metal sheets, and others, which, while being able to handle different models of workpieces, would have a very simple, compact structure; and would permit rapid change of the tools in the processing station. 
     Another object of the inventions is to accomplish a plant of the above type designed in such a way as to permit the use of a portal welding robot on the top of the body. 
     In accordance with the present invention the above mentioned objects are achieved by a plant for welding automotive vehicle bodies in a single processing station, to which said bodies are fed in succession. There is arranged in said station processing equipment for said bodies, comprising positioning, holding and optionally welding, means characterized in that said equipment is born by a pair of opposed stationary units, each of which includes a plurality of different tool assemblies mounted in a revolving manner so that the tools making up each individual assembly are presented selectively in operating position. 
     In accordance with another feature of the invention each unit, including the tool assemblies, is movable between a nonoperating position outside the path of travel of the body in the processing station, and an operating position, wherein the tool groups are designed to perform the processing of said body. 
     The structural and functional features of the invention and its advantages, as compared with the known art, are made more clearly understandable in the following description, and with reference to the annexed schematic drawings, which show an example of practical application of a plant in accordance with the invention. In the drawings 
     FIG. 1 is an elevational view illustrating an assembly plant incorporating the present invention, 
     FIG. 2 shows a schematic cross section along plane II--II of FIG. 1, 
     FIG. 3 shows an elevational view illustrating an individual unit having a plurality of tool groups according to the present invention, and 
     FIG. 4 is a cross section along plane IV--IV of FIG. 3. 
    
    
     With reference to the drawings, the plant which is the object of the invention, is indicated as a whole by reference number 10 and is made up structurally of a frame 11 bearing a pair of opposed stationary units 12. Said units 12 are mounted in a swinging manner around an upper shaft 13 around which they can be rotated at will driven by a motor 14 through a kinematic chain, e.g. with a screw 15 and a nut screw 16. 
     As may be seen clearly in the drawings the opposed units 12 are appropriately spaced so that there can pass between them a line indicated generally by reference number 17 for the programmed feeding of bodies 18 of automotive vehicles to a processing station 19. The line 17 will not be described and illustrated in greater detail as it may be of any type well known to those skilled in the art. 
     Each unit comprises a frame structure 20 (FIG. 3) bearing a plurality of tool assemblies 21 designed for performance of operations on a body 18. Said tools consist of elements shown schematically and indicated by reference number 22 which can perform for example positioning, holding and welding of the body. Even said elements 22, being of a known type, are not described and illustrated in greater detail. 
     In accordance with the invention each assembly 21 is mounted in a stepped manner and made to revolve by an actuator 24 in the directions indicated by the arrows in FIG. 4 around a shaft 23. More precisely as shown in FIGS. 2 and 4 the units 12 can be swung around the shaft 13 in the directions indicated by the arrows between two positions shown in broken and solid lines respectively. The position shown in broken lines is not operative and does not interfere with the path of travel of the bodies 18 in the station 19 while the position shown in solid lines is operative to bring the unit 12 opposite the body 18 to process it. The various positions of the unit 12 and the individual assemblies 21 are determined accurately by stop and positioning means of known type. 
     Reference number 25 indicates a floor-mounted welding robot while reference number 26 indicates a portal robot supported above the body by the same frame 11 and traversable on slides in a known manner. 
     Reference number 27 indicates generally the cabinets containing the feeding, command and control equipment of the plant. 
     Operation of the plant which is the object of the invention is clear from the above description and with reference to the drawings and is briefly as follows. 
     By means of the controls 14, 15 and 16 the opposed units 12 are swung into operating position so as to bring the associated tools 22 of each revolving tool assembly 21 into position facing the body to be processed. Said operating position is rigidly determined by intervention of suitable holding means. 
     At this point processing of the body can begin. 
     Upon each change of the body model arriving at the station 19 the assemblies 21 of tools 22 are selectively commanded to rotate so as to bring into operating position the equipment designed for processing the new body model. 
     The advantages of the plant in accordance with the invention may be briefly summarized as follows: (a) minimal time for adaptation of the plant to the various body models, (b) extreme simplicity of construction of the plant in comparison with the known ones and hence lower manufacturing costs, (c) reduced maintenance thanks to the small number of actuators used and total freedom from large moving masses, (d) increased accuracy because the units bearing the equipment are stationary, and (e) the components are practically wear-free because the plant is stationary.