Abstract:
A string of pocketed coil springs is formed by inserting compressed springs between upper and lower plies of a folded, preferably thermally weldable fabric. The springs are maintained in a compressed configuration while a longitudinal seam joins the free edges of the thermally welded fabric together. Subsequently, the compressed springs are allowed to relax into an expanded configuration after which a transverse seam is formed in the fabric between the adjacent springs thereby encapsulating each spring within a fabric pocket. The string of pocketed coil springs is advantageously formed without the need for reorienting the springs after being inserted between the plies of the fabric and thereby avoiding the disadvantages and complications associated with turning or reorienting the pocketed coil spring.

Description:
This is a continuation-in-part of U.S. patent application Ser. No. 09/293,221, filed Apr. 16, 1999 now abandoned and hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to spring assemblies for mattresses, cushions and the like, and, more particularly, to a method and system for making a string of connected individually pocketed coil springs for mattresses, cushions, spring units and the like. 
     Pocketed coil springs are often referred to as a Marshall construction in which each coil spring is encased within its own fabric sack or pocket. The sack or pocket is typically defined between two plies of a fabric strip connected together at intervals along transverse lines spaced along the strip. The two-ply fabric strip is generally formed by folding a strip of double width fabric upon itself along a longitudinal centerline, leaving the overlapped plies along the unjoined opposite edges of the strip to be connected to each other along a longitudinal seam to close the pockets defined between the transverse lines of connection after the springs are inserted between the plies. 
     A variety of techniques have evolved for the manufacture of pocketed springs, some contemplating the creation of the pockets within the fabric plies prior to insertion of the wire spring and others contemplating the insertion of compressed wire springs between the plies of the strip and the subsequent creation of the pockets by stitching or otherwise joining the two plies to each other along transverse lines between adjacent springs. Irrespective of the technique used, the fabric is closed around the spring after the insertion of the spring, usually by stitching or welding the two plies together along a line parallel to the free edges of the plies. Joining the plies together by stitching has largely been replaced in more recent times by the use of a heat sensitive fabric and ultrasonic welding techniques. Examples of known systems and techniques for manufacturing strings of pocketed coil spring are disclosed in U.S. Pat. Nos. 4,439,977; 4,234,983; and 5,613,287, each of which are incorporated herein by reference. 
     Specifically, in U.S. Pat. No. 4,439,977, a method and apparatus are disclosed for making coil springs enclosed within individual pockets in an elongate fabric strip comprised of two overlying plies capable of being thermally welded together. The fabric strip is fed along a guide path during which compressed springs are inserted between the plies with the axes of the springs substantially normal or perpendicular to the planes of the plies. Thereafter, the fabric plies are thermally welded together longitudinally and transversely while the spring remains compressed to form a string of pocketed coils. After thermal welding, the pocketed coils are passed through a turner assembly during which the springs are reoriented typically about 90° within the fabric pockets to positions wherein the axes of the springs are transverse to the fabric strip. 
     One specific disadvantage of this method of manufacturing pocketed coil springs is that during the turning process, springs tend to become entangled or hooked together and do not achieve their proper positions. As such, additional and costly labor is required to reorient and disentangle the springs to place them into their desired configurations and orientations. Even if the springs do not become entangled or hooked, difficulties may still arise in correctly aligning them to their desired positions with the longitudinal axes of the springs being substantially parallel to one another and the transverse seams defining individual pockets. 
     Another common problem with this type of operation is that during the turning of the pocketed springs, whether or not the springs become hooked or entangled and the turning process is successful, the fabric surrounding the spring is often damaged, torn, punctured or the like. In one form, the springs are beaten by paddles as disclosed in U.S. Pat. No. 4,439,977 to effect the turning of the spring within the pocket. Obviously, the repeated beating on the pocket with the paddles may cause significant damage to the fabric material and prove to be unreliable to accurately position the spring within the fabric pocket. When this happens, the damaged pocket should be repaired or removed from the string thereby interrupting the process and requiring significant operator intervention and down time for the production of pocketed coil springs. 
     Therefore, a need exists for a method and system for forming strings of pocketed coil springs which overcomes the above described disadvantages of the prior art and does not require the turning of the springs within the pockets for alignment of the spring axes in a generally parallel and ordered arrangement nor operator intervention to unhook or disentangle the springs nor repair the damaged fabric surrounding the springs. Further, a need has always existed to provide commercially viable methods and systems for producing strings of pocketed coil springs which are cost and labor effective by requiring a minimal amount of labor intervention and associated resources. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the above described and other disadvantages in the prior art by providing an improved method and system for producing strings of pocketed coil springs which are effective in performance, yet cost effective in that it requires a minimum amount of materials and labor. The manner in which the springs are inserted into the fabric and the formation of the pocket according to this invention avoids the need for turning or repositioning the springs within the pockets while still providing an efficient and reliable manufacturing system and associated method for reliably producing consistently aligned springs within undamaged fabric pockets. 
     The present invention preferably begins with the insertion of a compressed coil spring between upper and lower plies of a folded thermally welded fabric. The present invention is a continuous production process such that the fabric is indexed or pulled past a spring insertion station so that the compressed springs are individually inserted between the plies of the folded fabric at spaced intervals as the fabric passes the spring insertion station. The springs are maintained in a compressed configuration between the plies of the fabric while a longitudinal seam is formed in the fabric to join the two plies together proximate free edges of the plies opposite from a longitudinal fold line of the fabric. Since the fabric is a thermally weldable material, preferably the longitudinal seam is formed by a cooperating thermal weld head and anvil combination. After the spring has advanced past the longitudinal weld station, it is allowed to relax and expand within the fabric into an upright position in which a longitudinal axis of the spring is generally perpendicular to the longitudinal seam of the fabric. Preferably, the relaxation and expansion of the springs within the fabric is controlled by a pair of rotating members on opposite sides of the springs according to various alternative embodiments of this invention. The rotating members in presently preferred embodiments may be a pair of oppositely rotating wheels with axes of rotation generally parallel to the longitudinal axes of the springs. The wheels include a plurality of arcuate-shaped recesses which combine to partially surround each spring during the expansion. Alternatively, the rotating members may include a pair of bands each passing over a pair of spaced rollers. The fabric and springs pass between the bands and a separation distance between the bands increases in a downstream direction to thereby control the expansion of the springs between the bands. In either embodiment, the springs are supported during their expansion into an upright position. 
     After the springs have expanded within the fabric, individual pockets are formed preferably by a transverse weld head sealing the fabric between each of the springs generally parallel to the spring axes. The transverse seams are formed in the fabric to complete the individual pockets for the individual springs. Finally, a pair of opposing and rotating transport wheels indexes or moves the string of pocketed springs forwardly thereby advancing the fabric and enclosed springs through the various stations as described. 
     Advantageously, the orientation of the springs remains generally unchanged throughout the pocketing process so that reorientation, turning or the like of the springs within the pockets is avoided. Moreover, the longitudinal seam formed in the fabric is positioned on a side face of the individual spring pockets in the resulting string of pocketed coil springs thereby avoiding the problem known in the art known as “false loft”. False loft occurs when the longitudinally extending seams maintain the cover material at a certain distance away from the ends of the springs so that when the mattress is first purchased, this distance is fairly uniform. However, after the mattress or cushion has been in use for a period of time, the longitudinally extending seams or other excess fabric in the pocketed coil string may become crushed thus leaving areas or regions of depression. With continued use of the mattress or cushion, the entire support surface of the mattress or cushion will similarly be crushed and will appear substantially flat. A user may not realize the source of this phenomenon and consider it to be a defect in the mattress or cushion. 
     The problem of false loft is thereby avoided in the present invention by positioning the longitudinal seam of the string of springs on a side thereof while still avoiding the need to turn or reorient the individual springs within the pockets and the resulting damage to the fabric and other associated problems. 
     Another feature of this invention which also aids in the reduction of false loft and related problems is particularly useful for barrel shaped springs or other such springs which have a non-linear profile. With such springs, the transverse seam between adjacent springs in the string is shaped to conform to the profile of the springs and thereby produce a tighter, more conforming fabric pocket around the spring to avoid bunching or excess loose fabric around the spring. 
    
    
     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 of a schematic representation of a system and associated method according to a first embodiment for producing a string of pocketed coil springs of this invention; 
     FIG. 2 is a side elevational view of the system and method of FIG. 1; 
     FIG. 3 is a view similar to FIG. 1 of a second presently preferred system and associated method according to this invention; 
     FIG. 4 is a side elevational view of the system and method of FIG. 3; 
     FIG. 5 is a perspective view of a string of pocketed coil springs produced according to this invention; 
     FIG. 6 is a cross-sectional view of an individual coil spring encased within a fabric pocket as taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a side elevational view of a string of pocketed coil springs produced according to an alternative embodiment of this invention; and 
     FIG. 8 is a partial perspective view of a weld head used to weld a transverse seam in the string of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a first presently preferred embodiment of a system  10  and associated method for forming a string  12  of pocketed coil springs  14  according to this invention is shown. Fabric  16 , preferably thermally weldable as is well known in the art, is fed from a supply roll  18  around a roller  20  as shown in FIG.  1 . Alternatively, the fabric  16  could be cotton or another suitable material. The fabric  16  is folded generally in half longitudinally about a longitudinal fold line  22  which coincides approximately with a longitudinal centerline of the fabric  16 . The fabric  16  is folded about the longitudinal fold line  22  to produce a first, upper ply  24  and a second, lower ply  26  of fabric  16  each with a free edge  28  spaced from the longitudinal fold line  22 . The folded fabric  16  passes upper and lower input rollers  30 ,  32  prior to entering a spring insertion station  34 . The rollers  20 ,  30  and/or  32  may be rotationally driven. 
     The spring insertion station  34  includes a reciprocating insertion plunger  36  having a cup-shaped spring receiving leading end  38  to receive therein a compressed coil spring  14 . The plunger  36  extends to insert the compressed spring  14  between the plies  24 ,  26  and retracts to receive another compressed spring  14  for subsequent insertion. The spring  14  is formed and compressed and loaded onto the spring insertion plunger  36  and the fabric  16  is folded according to one of any number of well known systems and methods for doing so. Alternatively, the spring insertion station  34  may comprise two U-shaped profiles which keep the spring  14  compressed and lead the springs  14  inside the folded fabric  16 . In this method, the spring  14  is held with a horn (not shown) while the profiles return. 
     As the fabric  16  advances through the system  10 , the springs  14  inserted between the plies  24 ,  26  are maintained in a compressed configuration between upper and lower support plates  40 ,  42  on the upper and lower faces, respectively, of the fabric  16  as particularly shown in FIGS. 1 and 2. Preferably, the support plates  40 ,  42  are centered between the free edges  28  and longitudinal fold line  22  of the fabric  16  and may include a wider region  44  proximate the spring insertion station  34  which tapers downwardly to a region of smaller separation  46  between the plates  40 ,  42  as the fabric  16  and springs  14  advance through subsequent portions of the system  10 . 
     Additionally, a plurality of spaced alignment wheels  48  which are mounted for rotation proximate the longitudinal fold line  22  and free edges  28  of the fabric  16  control and direct the movement of the fabric  16  through the system  10 . The alignment wheels preferably include a plurality of projections  50  which engage the fabric  16  to maintain the movement of the fabric  16  in an aligned orientation with respect to the various stations and components of the system  10 . 
     A longitudinal seam forming station  52  is located downstream from the spring insertion station  34  proximate the free edges  28  of the fabric  16 , as shown in FIGS. 1 and 2. After the compressed springs  14  are inserted between the plies  24 ,  26 , the longitudinal seam forming station  52  joins the upper and lower plies  24 ,  26  of the fabric  16  together proximate their respective free edges  28  thereby initially enclosing the springs  14  within the fabric  16 . In a presently preferred embodiment, a longitudinal seam  54  is formed between a thermal weld head  56  which reciprocates downwardly and upwardly for cooperating welding engagement and disengagement, respectively, relative to an anvil  58  positioned below the lower ply  26 . The reciprocating weld head  56  and anvil  58  cooperate to form the longitudinal seam  54  in the fabric  16  by welding the respective plies  24 ,  26  together ultrasonically, thermally, or the like as is well known by those skilled in the art. Alternatively, the anvil  58  is moved reciprocally while the thermal weld head  56  remains stationary. The springs  14  remain compressed during the formation of the longitudinal seam  54  and weld with their longitudinal axes  60  generally perpendicular to the longitudinal seam  54 . It should be appreciated that other means for joining the plies  24 ,  26  together to form the seams such as stitching, staples, or other means are well within the scope of the present invention. 
     A first transport station  62  is located downstream from the longitudinal seam forming station  52  and, in a presently preferred embodiment, includes four transport bands  64 . Each band  64  passes over spaced forward and trailing rollers  66 ,  68 , at least one of which is rotationally driven. A first pair of bands  64   a  at the first transport station  62  contacts the fabric  16  proximate the longitudinal fold line  22  passing therebetween. Another pair  64   b  of transport bands  64  contacts the fabric  16  proximate the longitudinal seam  54  as shown in FIGS. 1 and 2. As the bands  64  pass around the spaced rollers  66 ,  68  in contact with the fabric  16 , the fabric  16  is pulled from the supply roll  18  through the upstream stations and is advanced toward a downstream spring expansion station  70 . 
     The compressed springs  14  are permitted to relax and expand within the fabric  16  at the spring expansion station  70 . In a first embodiment, the expansion of the springs  14  is controlled by a pair of oppositely rotating rotational members  72  on opposite sides of the springs  14  as shown in FIG.  1 . An axis of rotation  74  of each of the rotational members  72  according to the first presently preferred embodiment of FIG. 1 is generally parallel to the longitudinal axes  60  of the springs  14 . Each rotational member  72  includes a plurality of arcuate-shaped recesses  76 , each of which combine with a similarly configured recess  76  in the corresponding rotation member  72  on the opposite side of the spring  14  to partially surround each spring  14  and thereby control the expansion thereof. Additionally, the rotational members  72  assist in advancing the springs  14  and fabric  16  toward a transverse seam forming station  78  located downstream therefrom. 
     The transverse seam forming station  78  forms a transverse seam  80  in the fabric  16  between each of the adjacent springs  14  which have expanded within the fabric  16  from their compressed configuration. Preferably, the transverse seam forming station  78  includes a transverse seam weld head  82  and a cooperating transverse seam anvil  84  located on opposite sides of the forming string  12  of pocketed coil springs  14  from each other, as shown in FIG.  1 . As the springs  14  advance toward and through the transverse seam forming station  78 , the fabric  16  between the springs  14  is joined together thereby completing individual pockets  86  for each of the springs  14  and enclosing the springs  14  within the fabric  16 . Once again, it should be readily appreciated that other means for forming the transverse seam  80  such as stitching, staples or the like may be used within the scope of this invention. While the transverse seam  80  is formed, the fabric  16  is needed or gathered. As such, the string  12  of pocketed coil springs  14  must give in or contract somewhat to accommodate the seam forming process. This can be accomplished with an active mechanism such as a driven transport system or with in a passive manner such as friction between the fabric  16  and the transport rotational members  72 . 
     The longitudinal axes  60  of the springs  14  remain generally parallel to the transverse seams  80  in the fabric  16 . However, due to the expansion of the springs  14 , the longitudinal seam  54  formed at the free edges  28  of the fabric  16  is positioned generally on a side face  88  of the string  12  of pocketed coil springs  14  between top and bottom ends  90 ,  92  of the pocketed coil spring  14  as shown particularly in FIGS. 5 and 6. With the longitudinal axes  60  of the springs  14  generally aligned and parallel with one another within individual fabric pockets  86 , the present invention avoids the need for turning the springs  14  within the fabric pockets  86  as is required in many prior art systems. 
     Referring to FIGS. 5 and 6, the longitudinal seam  54  preferably becomes attached to the pockets  86  when the transverse seam  80  is formed by the transverse seam forming station  78 . As such, in the region of the fabric  16  proximate the transverse seam  80 , four layers of fabric  16  are welded together at the transverse seam forming station  78 . It should be appreciated that there are other methods to fix the seam  80  in this manner, for example, the longitudinal seam  54  could be positioned prior to entering the transverse seam forming station  78  even if it is not welded to the pockets  86  with the transverse seam  80 . Further, the longitudinal seam  54  may be located anywhere between the top and bottom of the string although it is shown in the drawings as approximately in the middle thereof. 
     A downstream or second transport station  94  preferably includes a pair of oppositely rotating transport wheels  96  each with an axis  98  of rotation generally parallel to the longitudinal axes  60  of the springs  14 . A plurality of arcuate recesses  100  on the periphery of the transport wheels  96  cooperate to at least partially surround the pocketed springs  14  and advance them from the upstream transverse seam forming station  78  for discharge and subsequent packaging, storage or processing into a mattress, cushion or innerspring unit. 
     An alternative embodiment of this invention is shown in FIGS. 3 and 4 and components of the system of FIGS. 3 and 4 which are similar to those of the first embodiment shown in FIGS. 1 and 2, are identified by identical reference numerals and the previous detailed description with respect to those items provided hereinabove is likewise applicable to the embodiment of FIGS. 3 and 4. The second presently preferred embodiment shown in FIGS. 3 and 4 includes divergent transport bands  102  located above and below the fabric  16  and enclosed springs  14  at the spring expansion station  70 . The transport mechanism could be embodied with wheels as in FIGS. 1 and 2 and/or transport bands as in FIGS. 3 and 4 which are located on the top and bottom of the string or the lateral side surfaces as desired. Each of the transport bands  102  of FIGS. 3 and 4 pass over forward and trailing rollers  104 ,  106 , as shown particularly in FIG.  4 . Furthermore, a separation distance between the transport bands  102  increases in a downstream direction thereby permitting the controlled expansion of the springs  14  positioned in the fabric  16  between the transport bands  102 . The relaxed and expanded springs  14  are then advanced to the downstream transverse seam forming station  78  so that the transverse seam  80  may be positioned between the adjacent springs  14  to complete the individual fabric pockets  86 . 
     An additional feature of this invention is shown in FIGS. 7 and 8 and is particularly adapted for use in constructing strings  12  of pocketed coil springs  14   a  having a barrel shaped configuration as shown in FIG.  7 . Barrel shaped springs  14   a  are well known in the industry and include a profile  108  in which the middle turns  110  of the spring  14   a  have a greater diameter than the top turn  112  and bottom turn  114  of the spring  14   a.  For example, the top and bottom turns  112 ,  114  of the barrel shaped spring  14   a  may have a diameter of about 1.625 inches and the middle turn  110  have a diameter of about 2.5 inches. When barrel shaped springs  14   a  are used in the string  12 , the transverse seam  80   a  adjacent to the spring  14   a  conforms to the profile  108  of the spring  14   a  as shown in FIG.  7 . With the transverse seam  80   a  conforming to the profile  108  of the spring  14   a  encased in the pocket a tighter pocket is produced with less loose fabric  16  in the string  12  and a better overall product, especially with springs  14   a  having a non-linear profile. With barrel shaped springs  14   a,  the transverse seam  80   a  adjacent thereto has a concave shape and because the transverse seam  80   a  is located between adjacent barrel shaped springs  14   a  the seam  80   a  may have a pair of outwardly facing concave shapes forming an X or similar configuration. A weld head  82   a  suitable for forming the transverse seam  80   a  is shown in FIG. 8 in which a number of studs  116  are arranged in the pattern shown so that adjacent studs  116  proximate the top and bottom of the weld head  82   a  are spaced farther apart than those in the middle to conform with the profiles  108  of the adjacent barrel shaped springs  14   a.  Although the transverse seam  80   a  of FIG. 7 is symmetric, other configurations are contemplated within the scope of this invention. Moreover, in another sense, this feature of the invention is useful not only for barrel shaped springs  14   a  to form a tighter, more conforming fabric pocket, but also for springs having a non-linear profile in general such as the barrel shaped springs and hour glass shaped springs in which the middle turns have a lesser diameter than the top and bottom turns. 
     From the above disclosure of the general principles of the present invention and the preceding detailed description of at least one preferred embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof.