1.  Field of the Invention
The present invention relates to a vertical assembly table for assembling composite structures, in particular, for assembling glass window structures. 
2.  Background Information
Assembly tables which tilt to reposition a workpiece are well-known in various arts.  For example, U.S. Pat.  No.  4,829,651 to Shirai discloses a tilting table for the manufacture of panels forming walls, roofs and floors.  U.S. Pat.  No.  4,492,016 to Smets et al.  discloses a tilting assembly table for pallets and the like.  Additionally, U.S. Pat.  No.  4,623,083 to Pagano discloses a pivotable assembly table having two pivotable portions for forming a board fence section.  The pair of pivotable table sections is sometimes referred to as a xe2x80x9cbutterfly tablexe2x80x9d due to the dual pivoting arrangement. 
Assembly tables have been created for automatically assembling insulated glass window structures in the form of butterfly tables.  An insulated glass window assembly generally consists of two identical glass workpieces or glass lites with an edge seal, such as a swiggle.  The glass seal is added to one glass lite after washing, but before conveying to the vertical assembly table.  A typical vertical assembly butterfly table is produced by Glass Equipment Development, Incorporated and designed for automatic operation.  The table automatically feeds glass lites in, aligns pairs of glass lites, then assembles a window structure. 
One disadvantage of prior art butterfly tables is that the pivoting structure incorporates the entire conveying assembly.  This significantly increases the weight of the portion being pivoted and the associated costs, design and complexity of the pivoting structure.  For example, the drive system of the conveyor must accommodate the pivoting conveyor.  Additionally, these factors work to increase the cycle time of the resulting table. 
It is an object of the present invention to overcome the problems with the aforementioned prior art.  It is another object of the present invention to design an efficient, cost-effective vertical assembly table designed to automatically assemble insulated glass window structures.  These objects are achieved by a vertical assembly table according to the present invention. 
The assembly table comprises two adjacent roller conveyor tables having a plurality of spaced rollers thereon.  The roller tables receive the glass lites to be assembled.  The glass lites proceed down the table until they hit an appropriate stop.  Separate pivoting subframes, each comprised of a plurality of lift arms positioned between the rollers of one roller table lift the two glass lites to be assembled away from the respective roller tables toward each other.  The glass lites are moved into alignment with each other.  One pivoting subframe includes pivotable alignment or abutment arms which will support both glass lites on a common structure simultaneously.  The other pivoting subframe includes a pushover assembly for pivoting one glass lite completely onto the other subframe.  Following transfer, the subframes will lower, with one subframe now lowering the assembled glass structure onto one of the two roller tables completing the assembly process.  The process can now be repeated for the next cycle. 
In one embodiment of the present invention, the vertical assembly table includes two independent DC servo driven roller conveyors each associated with a tilting subframe having a plurality of lift arms.  A pair of air cylinders are used with each subframe lifting assembly to lift the respective set of arms via a common pivot shaft.  The glass lite with the seal and the glass lite without the seal are conveyed separately under DC servo control into the assembly area of the table.  Both lites are squared and placed into precise alignment by a sequence of pneumatically operated squaring stops while being lifted in a vertical, folding orientation.  Bottom edge and lead edge squaring stops are used to initially make the two sheets parallel and the edges square.  In one embodiment of the present invention, a second lead edge squaring stop located near the middle of the table may be provided for double lite operation on the table.  Separate lites are assembled in a vertical orientation with the top edges mating first.  Arms of the pushover assembly are used to assist the final assembly by pushing the non-spacer lite against the seal of the spacer lite.  The non-spacer lite is preferably loaded onto lift arms having the pushover assembly so that it is the non-spacer lite being pivoted into position. 
The conveyor system of the present invention may utilize chain driven donut rolls.  Photoelectric sensors are used to notify the program logic controller (PLC) of the glass lite location during a process.  The sensors may be located at the entrance, center and exit of both conveyors.  Additionally, inductive proximity switches may be used to detect the mechanical completion of motions of the subframes in the process cycle. 
These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the figures wherein like reference numerals represent like elements throughout.