The invention relates generally to the construction of spring assemblies or the like. More particularly, it relates to the manufacture of strings of pocketed coil springs for use as the spring cores for mattresses, seat cushions or the like.
Mattress spring core construction over the years has been a continuously improving art with advancements in materials and machine technology. A well known form of spring core construction is known as a Marshall spring construction wherein metal coil springs are encapsulated in individual pockets of fabric and formed as elongate or continuous strings of pocketed coil springs. In an early form, these strings of coil springs were manufactured by folding an elongate piece of fabric in half lengthwise to form two plies of fabric and stitching transverse and longitudinal seams to join the plies of fabric to define pockets within which the springs were enveloped.
Recently, improvements in spring core constructions have involved the use of fabrics which are thermally or ultrasonically weldable to themselves. By using such welding techniques, these fabrics have been advantageously used to create strings of individually pocketed coil springs wherein transverse and longitudinal welds instead of stitching are used to form the pockets encapsulating the springs.
Once strings of pocketed springs are constructed, they may be assembled to form a spring core construction for a mattress, cushion or the like by a variety of methods. For example, multiple or continuous strings may be arranged in a row pattern corresponding to the desired size and shape of a mattress or the like and adjacent rows of strings may be interconnected by a variety of methods. The result is a unitary assembly of pocketed coil springs serving as a complete spring core assembly.
One improvement upon pocketed coil springs as described is a compound nested pocketed coil spring in which each pocket of a string includes two nested coil springs. In such designs, a first inner spring is typically shorter and smaller than a second outer spring. The first inner spring is nested within the second outer spring.
Spring core constructions employing compound nested pocketed springs provide the advantage of offering differing degrees of hardness to the spring unit. Varying degrees of hardness are usually achieved by varying the number of springs per unit area, commonly referred to as the xe2x80x9cspring countxe2x80x9d of the unit, or by changing the gauge of the wire from which the springs are manufactured. Compound nested pocketed spring coils are disclosed in PCT Application No. PCT/GB97/01759; U.S. Pat. Nos. 1,192,510; 2,567,520; 1,254,314; 882,654; and U.K. Patent No. 20,583. The inner and outer coil springs are nested so that the lower portion of the combined spring unit is reinforced by the inner spring making this portion of the unit much stronger than the upper portion. The upper portion may be flexible enough to provide a resilient and comfortable seating or sleeping surface and the lower portion strong enough to absorb abnormal stresses, weight concentrations or shocks without discomfort or damage.
Commonly, the inner spring of the nested compound spring unit is individually encased in a pocketed fabric material such as shown in U.S. Pat. No. 1,192,510, to minimize noise or interference during the flexing or compression of the compound spring unit.
Another advantage of such compound spring units when employed in a mattress or the like is that the inner spring of each compound nested spring unit is free floating or unsecured. As a result, when the mattress is inverted, the inner spring falls by gravity toward the lower face of the mattress. In this way, regardless of whether the mattress is inverted or flipped, the inner spring is always at the bottom portion of the spring unit and the compound nested spring units provide a varying degree of flexure from the top to the bottom of the spring unit.
Even though spring units constructed from strings of pocketed compound nested coil springs as described provide many advantages, the manufacture and construction of strings of pocketed compound nested coil springs has proven to be very complicated and often problematic resulting in increased expense for such strings. The construction of strings of pocketed coil springs with a single spring 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 U.S. Pat. No. 4,439,977 includes a spring coiler which forms a coil spring and deposits it about the upper end of an arcuate delivery horn. As such, the formed coil spring is delivered by gravity in a generally vertical orientation for subsequent compression and insertion into the pocketing fabric material.
Other systems for manufacturing pocket spring assemblies with single springs in each pocket 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. In each of these identified patent applications, a formed coil spring is deposited from the coiler in a generally vertical orientation for subsequent processing, including pocketing in a fabric or similar material. In the identified PCT application, a spring feeding assembly includes a chute which delivers successive springs emerging from the spring coiler into a vertical tube. Each vertically oriented spring in the tube is compressed by a ram and advanced by a plunger into a passage which maintains the spring in a compressed state for subsequent pocketing. The system in the previously identified U.S. patent application includes a split cylinder which receives a coil spring from a coiling machine. A compression member compresses the coil spring in the cylinder and the spring is pushed into the space between the lower and upper plies of the folded length of fabric. The split cylinder is supported for pivotal movement between an inclined position in line with the spring coiling machine for receipt of the spring and an upright generally vertical position. The cylinder is pivoted between a 45xc2x0 angle for receipt of the spring and a generally vertically upright orientation for delivery of the compressed spring between the plies of fabric. In each of these systems, the compressed spring is not substantially reoriented prior to insertion between the plies of fabric. In other words, the longitudinal axis of the compressed spring is generally vertical from the time it is delivered from the coiler until after it has been encapsulated in a pocket.
Another well known system for pocketing coil springs is commercially available from Spxc3xchl AG in Switzerland. Examples of such machines include the Spxc3xchl TF 90, 190 and 290 series machines. In such machines, a coiler forms a spring and deposits the spring into a trough in a generally horizontal orientation. The spring is then compressed horizontally by a compression paddle, rotated through 90xc2x0 and then while remaining compressed is inserted between the plies of a folded fabric which is subsequently formed into a pocket around the individual spring. One system for pocketing compound nested springs from a horizontal orientation is disclosed in U.K. Patent Application Serial No. 9726333.9, published as PCT Application No. WO99/30853 on Jun. 24, 1999 and hereby incorporated by reference.
While these systems provide opportunities to manufacture pocketed coil springs, there is a need to provide a system which can be utilized on a production basis and lend itself to further automation of the procedure for the manufacture of pocketed compound nested coil springs, particularly for known systems which deposit the formed spring in a vertical orientation prior to the pocketing procedure and as a result do not require re-orientation.
It has therefore been a primary objective of this invention to provide a method and system for the manufacture of strings of pocketed compound nested coil springs.
It has been a further objective of this invention to provide such a method and system which is reliable and cost effective for application in a fully automatic production facility.
It has been a still further objective of this invention to provide such a method and system which is particularly adapted for use with existing production systems for pocketing coil springs, particularly those in which the coil spring is deposited in a generally vertical attitude and therefore does not require re-orientation prior to being compressed and pocketed.
These and other objectives of the invention have been achieved by a system and method for forming a string of pocketed compound nested coil springs in which, in a first embodiment, a first smaller spring is initially formed and preferably pocketed. The smaller coil springs can be produced by known pocketing coil spring machines in which the individual pocketed springs are separated from the string and collected. Larger coil springs are also formed and then deposited onto a platform in a generally vertical attitude. In the first presently preferred embodiment of this invention, the pocketed individual smaller coil springs are then deposited vertically into one of the larger outer coil springs located in a vertical orientation on the platform. The inner coil springs pass through the upper terminal coil of the larger coil springs and into the interior of the larger coil spring thereby becoming nested within the larger coil spring. The resulting compound spring unit is then compressed from a generally vertical reciprocating plunger with the longitudinal axes of the inner and outer springs generally vertical and preferably co-linear. The compound compressed nested spring unit is then inserted between the plies of a folded fabric by an insertion plunger for subsequent pocketing.
In a second alternative presently preferred embodiment, the smaller and the larger coil spring are each compressed with the longitudinal axes of the springs generally vertical. Each coil spring is seated on the operating end of an insertion plunger and a separator plate is positioned between the insertion plungers and the smaller and larger compressed coil springs. The insertion plungers and separator plate extend the springs between the plies of a folded fabric pocketing material. Initially, the separator plate retracts thereby allowing the smaller coil spring to pass through the terminal end coil of the larger coil spring thereby becoming nested within the larger coil spring while still being compressed and contained between the plies of the pocketing material and in the insertion plungers. The insertion plungers then retract leaving the compressed and nested springs between the plies of the fabric material. Subsequently, the pocket is formed around the compound nested spring unit for the formation of a string of pocketed compound nested coil spring units.
In still another presently preferred embodiment of the invention, the larger coil springs are individually pocketed in fabric which is folded on both sides with a small overlap of material on a side of the string of pocketed coils. The individual larger coil springs are separated by a transverse or lateral seam preferably in the form of a thermal weld. A string of pocketed coil springs of this type is commonly referred to as a side seam string of pocketed coil springs because the opposing terminal free edges of the fabric overlap one another on a side of the string and the coils springs as opposed to the top or bottom thereof. As such, a longitudinal weld or seam in the string extending perpendicular to the transverse seams or welds is not required. Once the string of pocketed coil springs is formed, a compressed smaller inner coil spring, preferably pocketed, is inserted through the side seam and into the interior of the expanded larger coil spring in each pocket. The overlapping flaps of fabric are separated to provide access to the interior of the larger coil spring within the pocket for insertion of the compressed smaller inner coil spring.
In other presently preferred alternative embodiments of the invention, the outer larger coil spring is formed or coiled around the smaller inner coil spring which may be compressed, expanded, pocketed or simultaneously being formed within the developing interior of the larger outer coil spring. Preferably, in specific embodiments, the outer coil spring is formed with left-hand or right-hand turned convolutions and the inner coil spring is formed with the opposite hand turned convolutions to avoid interference between the inner and outer coil springs if the inner coil spring is not pocketed.
As a result of the present invention, systems and methods for manufacturing strings of pocketed compound nested coil springs are provided which are compatible with conventional machinery for pocketing coil springs in a fully automatic production capability.