Abstract:
Spring sets each include a pair of coil springs joined together by a connecting wire and are encased in individual fabric pockets such that the connecting wire joining the coil springs spans an otherwise empty fabric pocket. A spring unit, mattress or the like includes a number of such pocketed spring sets with the connecting wire being alternately positioned near a top face or a bottom face of the spring unit. The pocketed coil spring unit can be used to form a mattress or other spring assembly of pocketed coil springs wherein every third pocket is left empty. The connecting wire spreads the load across the empty pocket and distributes the load to the adjacent springs. The absence of one-third of the springs that are normally in a mattress drastically reduces material costs without diminishing performance.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to spring units for use in mattresses, spring upholstered furniture and the like and, more particularly, to an improved pocketed coil spring unit and associated method of manufacturing such a spring unit. 
     A well known type of spring assembly includes a number of discrete coil springs, each of which is enclosed in a fabric pocket in a length of folded fabric material. Longitudinal axes of the spring coils are generally parallel with one another so that the top and bottom end turns of the coil springs define top and bottom faces of the spring unit. A spring assembly can be fabricated from such a spring unit by forming rows of the pocketed coil springs and binding or adhering the individual rows together to form a mattress or spring assembly. 
     This type of spring assembly is commonly referred to as a pocketed spring unit due to the fact that each spring is contained within an individual pocket of fabric material. The construction of strings of pocketed coil springs in each pocket is well known in the art and, for example, disclosed in U.S. Pat. No. 4,439,977 which is hereby incorporated by reference in its entirety. The system disclosed in that patent includes a spring coiler which forms a coil spring which is subsequently compressed and inserted between the plies of folded pocketing fabric material. Other systems for manufacturing pocketed coil spring assemblies are disclosed in PCT Patent Application No. WO94/18116 and U.S. patent application Ser. No. 08/927,051 filed Sep. 10, 1997, each of which are expressly incorporated herein by reference. 
     Pocketed spring units are generally recognized to have a unique and particular luxurious feel to them and mattresses manufactured of such pocketed spring units provide a feeling of softness without lacking spring resilience or support. Mattresses and similar articles constructed of pocketed spring units are often considered a high-end type of product because of the added benefits and features of the pocketed coil springs. Mattresses and the like of this type can be more costly to manufacture and assemble as a result of the considerable amount of time and labor which is involved in their manufacture, together with the fact that the method of fabrication and assembly of such pocketed spring units can be complicated, particularly in an automated process. 
     While known systems provide an automated method for producing and assembling pocketed spring units, the increased cost of materials and associated components for mattresses and other items incorporating such spring units can be a detriment to the commercial success of these products, even though they do provide enhanced softness and support as previously described. 
     Therefore, there is a need for an improved pocketed spring unit and associated method of manufacture which offers all the advantages of known pocketed spring units without the associated higher manufacturing costs and related disadvantages of known pocketed spring units. 
     SUMMARY OF THE INVENTION 
     These and other objectives of the invention have been obtained by an improved pocketed coil spring unit and associated method of manufacture for mattresses, spring upholstered furniture and the like according to this invention. 
     In one embodiment of this invention, a number of spring sets, each of which includes a first coil spring and a second coil spring which are joined together by a connecting wire at corresponding end turns of the first and second coil springs, are utilized. Each spring set is formed from an integral piece of spring wire. The spring sets are each encased in fabric pockets such that a grouping of adjacent fabric pockets includes first, second and third pockets which are serially connected with the third fabric pocket being between the first and second fabric pockets. The first coil spring of each spring set is inserted into the first fabric pocket and, likewise, the second coil spring of each spring set is inserted into the second fabric pocket. The connecting wire joining the coil springs spans the third fabric pocket which, in one embodiment of this invention, is empty with the exception of the connecting wire. The spring unit includes a number of such pocketed spring sets with the connecting wire being alternately positioned near a top or a bottom of the spring unit. 
     The pocketed coil spring unit of this invention can be used to form a mattress or other spring assembly of pocketed springs wherein every third pocket is left empty without a spring therein. As such, one goal of the invention is achieved by reducing the total amount of wire needed to form a pocketed spring coil mattress. The absence of one-third of the springs that are normally in a mattress drastically reduces manufacturing costs. Moreover, the ability to skip every third pocket does not diminish performance of a pocketed coil mattress because of the connecting wire joining the spring coils of each spring set. The connecting wire bridges over or spans the empty pocket so that when someone sits or lays on the mattress, the connecting wire spreads the load across the empty pocket and distributes the load to the adjacent springs. Advantageously, the connecting wire is located on the top and bottom surfaces of the spring unit so that the mattress or the like may be conveniently flipped top to bottom without altering its performance characteristics. 
     Another aspect of this invention is a method for manufacturing the pocketed coil spring unit such that each spring set is manufactured from a wire coiler which initially forms the first coil spring from one end turn to an opposite end turn of that coil spring. A connecting wire is then formed to project from the end turn of the first spring coil. Subsequently, the opposite end turn and the remainder of the second spring coil is formed. As such, a connecting wire joins opposite end turns of the first and second coil springs. The coil springs are then pivoted or manipulated relative to one another so that one coil spring is inverted, pivoted or manipulated relative to the other so that the connecting wire joins corresponding end turns of the two joined coil springs at either the top or bottom of the spring set depending upon its orientation. The spring set with the connecting wire joining corresponding end turns of the two coil springs is then inserted into the fabric pockets as previously described with the connecting wire spanning an empty pocket positioned between the two pocketed and joined coil springs. The pocketed spring sets are then arranged and assembled into the desired spring unit, mattress or the like. 
     As such, with this aspect of the invention, standard spring coiling machines can be used to produce the spring sets for use in spring units, mattresses or the like thereby avoiding the need for additional capital costs, machinery and complicated manufacturing processes and techniques. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objectives and features of the invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a top plan view partially broken away of a prior art pocketed coil spring mattress; 
     FIG. 2 is a top plan view partially broken away of a pocketed coil spring mattress according to one embodiment of this invention; 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG. 2 of a row of pocketed coil springs partially broken away; 
     FIG. 4A is a diagrammatic representation of a manufacturing method for a spring set including two joined coil springs according to one embodiment of this invention; 
     FIGS. 4B-4C are alternative configurations of spring sets resulting from the method of FIG. 4A; 
     FIG. 4D is a perspective view of a portion of a string of pocketed coil springs according to one embodiment of this invention; and 
     FIG. 5 is a top plan view of a portion of a mattress showing the springs sets arranged therein according to one embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a prior art mattress  2  is shown which includes a number of rows  4  of pocketed coil springs  6 . Each pocket  8  in the rows  4  of pocketed coil springs  6  encases a coil spring. Typically, in prior art pocketed coil spring mattresses  2 , each pocketed coil spring  6  in each row  4  is aligned with an adjacent pocketed coil spring  6   a  of an adjacent row  4   a  to form a generally rectangular pattern as shown in FIG.  1 . 
     Referring to FIG. 2, a pocketed spring unit  10 , such as a mattress or the like, according to one embodiment of this invention, is shown. The mattress  10  of FIG. 2, includes rows  12  of serially connected fabric pockets  14  as is well known in the industry. However, each grouping  16  of three adjacent fabric pockets  14  includes two coil springs  18   a ,  18   b  encased by two spaced fabric pockets  14   a ,  14   b  with an empty fabric pocket  14   c  therebetween which does not enclose a coil spring  18  (FIG.  3 ). Further, the coil springs  18  in each row  12  of the mattress  10 , as shown in FIG. 2, are offset with respect to the coil springs  18  in each adjacent row  12   a . As such, each pair of adjacent coil springs  18  that border an empty pocket  14   c  form a hexagonal pattern or configuration  20  with coil springs  18  from the adjacent two rows  12   a ,  12   b.    
     One advantage of the spring arrangement and placement of coil springs  18  in the pocketed fabric material, according to the embodiment of this invention shown in FIG. 2, is the reduction of the total amount of coil springs  18  and wire used to form the pocketed coil spring mattress  10  and the associated costs, labor and expenses while still maintaining the same performance characteristics as those of known pocketed coil spring mattresses  2  and the like. For example, the spring unit  2  with a pocketed coil spring arrangement according to the prior art, as shown in FIG. 1, includes 191 coils per square yard in an array of 14×15 coil springs in 1.099 square yards. In contrast, the pocketed coil spring mattress or spring unit  10  of this invention as shown in FIG. 2, requires 160 coils per square yard in a 10×16 arrangement of coils. Based on these coil spring requirements, this invention provides a reduction in the coil spring requirements on the order of 16% and the associated costs and labor savings. 
     Moreover, the performance characteristics of the spring unit, mattress  10  or the like, according to this invention, are maintained because of the coil spring arrangement according to one embodiment of this invention. For example, in FIG. 3 the row or string  12  of pocketed coil springs  18  is shown. Each coil spring  18  includes a number of turns  22  and spaced end turns, such as a top end turn  22   a  and a bottom end turn  22   b  of each coil spring  18 . It should be readily understood that terms such as top, bottom and the like as used herein are for reference only and should not be considered as limitations on this invention or the scope of the following claims. 
     Each coil spring  18  is part of a spring set  24  which includes a first coil spring  18   a  and a second coil spring  18   b  that are joined together by a connecting wire  26 . Specifically, in one embodiment, the connecting wire  26  joins corresponding end turns  22   a  or  22   b  of the coil springs  18   a ,  18   b  of each spring set  24 . Each coil spring  18  is encased in a fabric pocket  14 , as shown in FIG.  3 . The fabric pocket  14  typically is formed between the folded plies of a fabric material  30 . The pocket  14  is defined by spaced transverse seams or welds  32  and a longitudinal seam or weld  34  which joins the free ends  36  of the plies  28  of the folded fabric material  30 . 
     Each coil spring  18  of each spring set  24  is encased or inserted into an individual fabric pocket  14  of this type. Specifically, in each grouping  16  of three adjacent serially connected fabric pockets  14   a ,  14   b ,  14   a , one of the coil springs  18   a  from each spring set  24  is inserted into a first fabric pocket  14   a  and the other coil spring  18   b  is inserted into a second fabric pocket  14   b  with an empty third fabric pocket  18   c  positioned therebetween. The intermediate or third fabric pocket  18   c  does not have a coil spring and is left empty with the exception of the connecting wire  26  joining the coil springs  18   a ,  18   b  of each spring set  24 . The connecting wire  26  spans the third fabric pocket  14   c  ,  18   c  of each grouping  16 . Due to the connecting wire  26  which spans the intermediate fabric pocket  14   c , the support provided by the spring unit or mattress  10  according to this invention is maintained because the load applied to the connecting wire  26  in the proximity of the third fabric pocket  14   c  is distributed to the joined coil springs  18   a ,  18   b  of the associated spring set  24 . 
     In one embodiment of this invention, as shown in FIGS. 3 and 5, the connecting wire  26  of each spring set  24  is alternately positioned relative to a top face  38  and a bottom face  40  of the mattress, spring unit  10  or the like. Specifically, the connecting wire  26  of a first spring set  24   a  is positioned proximate the bottom face  40  of the mattress  10  and the connecting wire  26  of the next adjacent spring set  24   b  in the row  12  is positioned proximate the top face  38  of the mattress  10 . Subsequent spring sets  24  in the row or string  12  of pocketed coil springs  18  are likewise alternately positioned thereby providing for consistent performance for the mattress, spring unit  10  or the like irrespective of its orientation. The connecting wire  26  is alternately located on top and bottom surfaces  38 ,  40  of the spring unit, mattress  10  or the like so that it can be conveniently flipped to-to-bottom and bottom-to-top without altering the performance characteristics. 
     In one embodiment of the mattress  10 , a border  42  (FIG. 5) is used around the perimeter of the mattress  10 . The border  42  may be a wire, foam or other material commonly used in the industry to contain or bind the end coil springs  18  of each row together and help maintain their positioning and spatial relationships. With a border  42 , individual pocketed coil springs  19 , as shown in FIG. 2, would likely not be required to maintain coil spring positions, but could be used as desired. Additionally, the individual rows  12  are glued, adhesively attached, bonded or mechanically joined to the adjacent row  12   a  as is well known in the art. 
     Referring to FIGS. 4A through 4D, one embodiment of a method of making the spring set  24  according to this invention is shown. One known method for forming a coil spring utilizes a coiling machine to form a length of coil wire into the coil spring as disclosed in U.S. Pat. No. 4,439,977, for example. This invention utilizes the coiling machine to form an integral piece of wire into a first coil spring  18   a , as shown in FIG. 4A, that has a top end turn  22   a , a bottom end turn  22   b  and a number of intermediate turns  22   c , and a connecting wire  26  which, in one embodiment, is generally linear, as shown in FIG. 4A, and projects from the top end turn  22   a  and extends to a bottom end turn  22   b  of a second coil spring  18   b . The spring sets  24  are formed in this manner from a single integral piece of coil wire such that opposite end turns  22   a ,  22   b  of two coil springs  18   a ,  18   b  are joined integrally together by the connecting wire. Each coil spring  18  of the spring set  24  formed by the coiler, as shown in FIG. 4A, has a longitudinal axis L 1  which is generally parallel to and spaced from the longitudinal axis L 1  of the joined coil spring. Similarly, each coil spring  18  has a lateral axis L 2  which is parallel to and spaced from the lateral axis L 2  of the joined coil spring  18 . 
     Subsequently, one of the coil springs  18 , for example the first coil spring  18   a , as shown in FIG. 4A, is manipulated in such a manner that the top end turn  22   a  becomes the bottom end turn  22   b , as shown in FIG.  4 B. Specifically, the first coil spring  18   a  is pivoted or rotated in the direction of arrow A approximately 180° about an axis defined generally by the connecting wire  26  relative to the second coil spring  18   b  into the configuration of the spring set  24  shown in FIG.  4 B. As such, the spring set  24  as shown in FIG. 4B has the connecting wire  26  joining corresponding bottom end turns of the first and second coil springs  18   a ,  18   b.    
     After the coil springs  18  are manipulated relative to one another, their longitudinal axes L 1  remain generally parallel and spaced with respect to each other; whereas, the lateral axes L 2  of the coil springs  18  become generally co-linear, as shown in FIG.  4 B. After the spring set  24  is manipulated so that the connecting wire  26  joins corresponding end turns  22   a  or  22   b  of the coil springs  18 , the spring set  24  may be inverted so that the connecting wire  26  is on the top or bottom of the spring set  24 , as shown by comparison of FIGS. 4B and 4C. Subsequently, the spring set  24  is encased within fabric pocket material  30 , as shown in FIG.  4 D. 
     As a result of this invention, the numerous advantages of pocketed coil spring mattresses, spring units  10  and the like are achieved while reducing the total amount of wire needed without detrimentally impacting the performance characteristics thereof. Further, a method of producing such a spring unit  10  is obtained without complicated procedures, techniques, machine requirements and the like.