This invention relates to foundation units, and in particular to a foundation unit which may be fabricated in a factory and then shipped in a relaxed state to be later elevated and completed.
U.S. Pat. No. 4,377,279, assigned to the assignee of this application, pertains to a foldable steel wire foundation unit such as a box spring. The foundation unit is composed of a rigid bottom substructure, a flat top wire grid structure, and a plurality of spaced, parallel rows of substantially flat support members extending between the grid wire top bearing structure and the bottom substructure. Because the support members are substantially flat and are hingedly secured to the grid wire top bearing structure, the foundation unit can be fully assembled at a factory and then shipped to the customer in a relaxed orientation. The customer then raises the unit to a fully expanded orientation and locks the structure in place by a plurality of oppositely-directed struts. The foundation unit is then padded and covered with fabric in a conventional fashion.
U.S. Pat. No. 4,770,379, also assigned to the assignee of the present application, is an improvement over the structure of the '279 patent. The '379 patent is directed to a different type of wire support member for a foundation unit, in that the wire supports comprise oppositely oriented sinuous wire segments. The wire segments provide some resiliency, and similar to the '279 patent, the foundation unit is capable of being relaxed for shipping and later expanded for completion and ultimate use.
U.S. Pat. No. 4,903,947, also assigned to the assignee of the present application, is a further improvement over the foundation units disclosed in the '279 and '397 patents. This patent employs a series of sinuous wire elements which are secured to the top bearing structure in such a way that the foundation unit can also be relaxed for shipping. Auxiliary stabilizers such as struts are unnecessary to retain the foundation unit in an expanded orientation.
While the structures of U.S. Pat. Nos. 4,377,279; 4,770,397 and 4,903,949, the disclosures of which are incorporated herein by reference, provide quite adequate foundation units, they do suffer some deficiencies. In all instances, the intermediate wire supports must be clipped in some manner to the flat grid wire top bearing structure. Use of individual clips is costly. In addition, some of the structures cannot remain standing without use of struts, an additional expense in both fabrication and ultimate formation of the foundation unit. In addition, the foundation units require the typical nine rows of supports, one row at either end and seven intermediate rows.