Improvements in forming a resilient core

Abstract

A method of forming a resilient unit, such as a mattress core, comprises successively joining together discrete strings 130a, 130b of pocketed springs 110, side to side, to build an array of such spri

Description

The present invention relates to improvements in a method and apparatus for forming a resilient core and is concerned particularly, although not exclusively, with a method and apparatus for forming a glue-free mattress core. Mattress cores are typically formed from coil springs encased in pockets. Referring to Figure 1, the springs 10 are initially placed between sheets or plies of pocketing material, which could be a single sheet 20 folded into two. The sheets are then glued, stitched or welded along their edges and between the springs to encase the springs in individual pockets. Figures 2 and 3 are respective schematic side and perspective views of a so-called "string" 30 of springs formed in this way. According to the prior art method, the strings 30 are then glued together along the cylindrical surfaces of the pocketed springs to form an array 40 as shown in Figure 4. Such an array, of an appropriate length and width, is used as a mattress core. Glue is expensive and cannot easily be recycled, so in recent times efforts have been made to find alternative means of holding the strings together. However, thus far, many such alternatives have either proved inflexible or expensive to manufacture or both. Some prior art methods utilise ultrasonic welding to join together the pocketing material from adjacent strings of springs. In this technique, a sonotrode (or horn) is brought 1 together with an anvil, with the two layers of material sandwiched therebetween. The sonotrode is energised, and the resulting vibrations fuse together the pocketing material from the two strings. A problem with which the present invention is concerned is how to quickly and efficiently weld successive strings of springs together to form a resilient unit, such as may be used in, or as, a mattress core. Embodiments of the present invention aim to provide a method and an apparatus for forming a resilient core in which at least some of the problems with the prior art are at least partly addressed. The present invention is defined in the attached independent claims, to which reference should now be made. Further, preferred features may be found in the sub-claims appended thereto . According to one aspect of the present invention, there is provided a method of forming a resilient unit, the method comprising successively joining together a plurality of discrete strings of pocketed springs, side to side, to build an array of such springs, wherein successive discrete strings are introduced to the array alternately from substantially opposed directions. Preferably, the strings are joined together by welding portions of pocketing material between alternate pairs of springs of one string to corresponding portions of pocketing material between alternate pairs of springs of an adjacent string. In a preferred arrangement, the pocketing material portions that are joined together are alternately offset in successive adjacent pairs of joined strings, more preferably offset by one spring width. Preferably, a first and a second set of pairs of sonotrodes and anvils are brought together alternately to weld successive strings to the array. The strings may be introduced, in turn by first and second, more preferably upper and lower, carriages. Preferably, anvils of the first set are arranged to approach the array from above and anvils from the second set are arranged to approach the array from below. The sonotrodes may be arranged to approach the array from a front side. Alternatively, sonotrodes of the first set are arranged to approach the array from above and sonotrodes from the second set are arranged to approach the array from below. The anvils may be arranged to approach the array from a front side. The anvils may be retractable from the carriage(s) and / or are arranged for independent movement with respect to the carriage (s) . In a preferred arrangement, the successive discrete strings are introduced to the array alternately from above and below. More preferably, the method comprises welding one string to the array while preparing the next string to be introduced to the array from an opposed direction. The method may include introducing strings from string supply stations on opposed sides of the array. There may be plural string supply stations on one or both sides of the array. Different string supply stations may be arranged in use to supply stings comprising springs of different type or characteristic, such as (but not limited to) different stiffness . In this way, an array may be built that has different portions or regions, containing springs of different type or characteristic. As an example, an edge portion of the array may contain strings of springs that are of a different characteristic from those of a central or main region of the array. In one preferred example, the edge of the array may comprise springs that are stiffer than those in the main or central portion of the array. In another example, the array may be built up with zones containing strings of springs that are of different characteristic. This can often be desired where a certain portion of the array, or mattress, is to have a stiffer characteristic than another. A further example is where the mattress is to be shared, and the users have different requirements, so that one half of the mattress can be stiffer than the other half. According to another aspect of the present invention, there is provided apparatus for forming a resilient unit, the apparatus comprising joining means for joining together a plurality of discrete strings of pocketed springs, side to side, to build an array of such springs, wherein the apparatus is arranged to introduce successive discrete strings to the array alternately from substantially opposed directions . Preferably, the joining means comprises welding tools arranged to weld together portions of pocketing material between alternate pairs of springs of one string to corresponding portions of pocketing material between alternate pairs of springs of an adjacent string. The apparatus is preferably arranged to join together portions of pocketing material that are alternately offset in successive adjacent pairs of joined strings, more preferably offset by one spring width. The welding tools preferably comprise a first and a second set of pairs of sonotrodes and anvils that are brought together alternately to weld successive strings to the array. Preferably, the anvils of the first set are arranged to approach the array from above and anvils from the second set are arranged to approach the array from below. The sonotrodes may be arranged to approach the array from a front side. Alternatively, the sonotrodes of the first set are arranged to approach the array from above and sonotrodes from the second set are arranged to approach the array from below. The anvils may be arranged to approach the array from a front side . In a preferred arrangement, the apparatus is arranged to introduce successive discrete strings to the array alternately from above and below. More preferably, the apparatus is arranged to weld one string to the array while preparing the next string to be introduced to the array from an opposed direction. The apparatus may include string supply stations on opposed sides of the array. There may be plural string supply stations on one or both sides of the array. The apparatus may comprise different string supply stations arranged in use to supply stings comprising springs of different type or characteristic, such as (but not limited to) different stiffness. According to a further aspect of the present invention, there is provided a resilient core unit made in accordance with a method according to any statement herein or by apparatus according to any statement herein. The invention also includes a mattress including such a core. In a further aspect, the invention provides a computer programme product on a computer readable medium, comprising instructions that, when executed by a computer, cause the computer to perform a method according to any statement herein. The invention also comprises a program for causing a device to perform a method according to any statement herein. The invention may include any combination of the features or limitations referred to herein, except such a combination of features as are mutually exclusive, or mutually inconsistent. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figures 1 -4 show strings of pocketed springs as used in a resilient core unit; Figures 5-10 show, schematically, steps in a method of assembling a resilient unit, according to an embodiment of the present invention; Figure 11 is a schematic front view of an apparatus for assembling a resilient unit, in a first configuration; Figure 12 shows the apparatus of Figure 11 in a second configuration; Figure 13 shows, schematically, a part of the apparatus of Figures 11 and 12 from above; Figure 14 is a schematic flowchart representing the operation of the apparatus of Figures 11-13; Figure 15 shows schematically an example of a mattress with an edge region of a different characteristic to that of the rest of the mattress, in accordance with an embodiment of the present invention; Figure 16 shows schematically an example of a mattress with a zone having a different characteristic to the rest of the mattress, in accordance with another embodiment of the present invention; and Figure 17 shows schematically a mattress having two halves of different characteristics. The following description with reference to Figures 5-10 is of a method of assembling a resilient unit, in accordance with an embodiment of the present invention. The strings of springs are represented in the drawings as much shorter than would be the case with most actual resilient units, such as may be used in, or as, mattresses. The short form of string has been used merely for exemplary purposes. Turning to Figure 5, this shows, schematically from above, a first string 130a of springs 110 which is brought from a left side of the drawing towards the centre in the direction of arrow Al. A second string 130b is then brought from the opposite side, in the direction of Arrow A2. Figure 6 shows the two strings in side-by-side juxtaposition. A set of ultrasonic welding horns, known as "sonotrodes" 150 are introduced from a front side in the direction of Arrow A3. The sonotrodes 150 approach the string 130b at positions between springs 110 towards the portions P of pocketing material that extend between adjacent springs. The sonotrodes 150 are spaced, so that only alternate portions P of pocketing material are approached. At corresponding portions P of the pocketing material between adjacent springs on the second string 130b, a first set of welding anvils 160a is positioned. Preferably, these anvils approach their positions from below the strings, so that they travel in a direction substantially parallel with the axes of the springs (not shown). The sonotrodes 150 are then pressed against the anvils 160a and an electrical signal applied to the sonotrodes causes the pocketing material of the adjacent strings to become fused together. Figure 7 shows the welds W formed as a result of the coming together of the sonotrodes 150 and anvils 160a. Notably, the pushing together of the portions of pocketing material that become welded together results in the portions P between adjacent pairs of springs becoming pulled tight and displaced from their usual centre locations. The result is repeated sets, or clusters, of four springs known as quads Q defining openings 0 at the centres thereof. Next (Figure 8) a third string of springs 130c is introduced from the left in the direction of Arrow Al. Figure 9 shows the sonotrodes 150 being introduced, as well as a second set of anvils 160b. In this step, the bank of sonotrodes 150 has been shifted sideways by a single spring pitch, so that the sonotrodes 150 and anvils 160b come together at positions that are shifted one spring away from the earlier welds (along the length of the strings), so that the portion P of pocketing material from the new string 130c becomes welded to the portion of pocketing material that was pulled tight and displaced during the previous welding operation. The bank of sonotrodes shifts sideways back and forth at each welding cycle. Figure 10 shows the process several steps later, when a resilient unit 140 has been made up from several strings, with each string being joined to its predecessor and its successor (except the first and last such strings) by welds that are offset (along the length of the strings) by one spring. The resulting unit has quads Q defining staggered openings 0 between the adjacent strings. Figure 11 shows schematically a front view of a part of an apparatus, generally at 200, for performing the method described above. The apparatus is mounted in a frame F and comprises the two sets 160a and 160b of ultrasonic welding anvils, respectively above and below a resilient unit 140 (shown end-on). The two sets of anvils are moveable in an up and down direction represented by Arrows A4. Note that the anvils 160a and 160b are each mounted on respective carriers 170a, 170b and that they are offset with respect to one another along the width of the unit 140 (along the length of the strings forming the unit) . The sonotrodes are omitted from this drawing in the interests of clarity. Strings 130 of springs are introduced, in turn, to the welding stage by upper and lower carriages respectively (omitted from the drawings for reasons of clarity). In the example shown, an upper carriage introduces a string from the left side and then the introduced string is lowered to a welding position, at a centre line C along with the upper set of anvils. At substantially the same time as the upper string is being welded to the unit 140, a lower string 130 is being prepared for subsequent introduction on a separate carriage from the right and at a lower position. Figure 11 shows the apparatus 200 in a first welding configuration. An upper string, together with the upper set of anvils 160a has been lowered, with the anvils 160a entering into positions between alternate pairs of springs in the unit 140 at the centre line C. The sonotrodes are omitted from the drawing. As the string is welded, the next string 130 is being prepared for introduction from below and to the right side. Conveniently, the movement of the sonotrodes 150, as they press the (as yet) unattached string of springs against the rest of the spring unit, has the effect of indexing the unit forwards at each welding cycle. Figure 12 shows the apparatus in the next welding configuration, in which the set 160b of anvils has been raised into positions between alternate pairs of springs in the unit 140, offset from the spring pairs of Figure 11, along with the next string 130 from below and right. Again, the sonotrodes are omitted from the drawing. Figure 13 shows a part of the apparatus 200 from above. A set of welding sonotrodes 150, each mounted on its own pneumatic actuator 155, are disposed at the rear of the resilient unit, represented in this case by a single string of springs 130. The sonotrodes 150 are arranged in a bank that can shuttle sideways, back and forth by a single spring pitch, in the direction shown by Arrow A5. The set 150is advanced towards the webs of pocketing material between the springs for welding, and then retracted. At the next cycle, the bank of sonotrodes is shifted sideways by a single spring width before being advanced again at the next cycle, and so on so that in successive operations, alternate pocketing material portions P are welded to their neighbours in the next string, in the manner depicted schematically in Figures 5-10 . Turning to Figure 14, this represents schematically some method steps according to an embodiment of the present invention. At Step 1000, the process begins. At Step 1001 a first string of springs is supplied, in this example from an upper Left Hand Side (LHS) position. At Step 1002, the first string and (upper) Set 1 anvils are lowered to a welding position (at centre line C of Figures 11 and 12. Then, at Stage 1003 the sonotrodes are introduced and the string is welded to a previously placed string at the centre line, wherein the Set 1 of anvils occupies positions between alternate pairs of springs in the second string, and the two thus-joined strings form a resilient unit that is indexed by the pressing of the sonotrodes. Substantially simultaneously, at Stage 1004, another string is supplied from a lower, Right Hand Side (RHS) position. Then, at Step 1005, the lower string and a Set 2 of anvils are raised to the centre line, wherein the Set 2 of welding anvils occupies positions between alternate pairs of adjacent springs in the first string, offset from the Set 1 positions by a single spring width. Then, at Stage 1006 the sonotrodes are introduced - at positions alternate from the previous welding positions, and the string is welded to the previously placed string at the centre line, with the unit being indexed. Meanwhile, substantially simultaneously, at Stage 1007, another string is supplied from a upper Left Side position. At Step 1008 a judgement is made as to whether the unit is complete. If the unit is judged to be complete at Step 1008, the process ends at Step 1009. If the unit is judged to be incomplete, the process returns to Step 1002. Whereas the tools 150 and 160 are described in this example as, respectively sonotrodes and anvils, their positions could be reversed. Indeed, the example of ultrasonic welding apparatus could be replaced by thermal bonding, or heat-sealing tools. The methods provide by the embodiments described above allow individual strings 130 to be introduced to the unit as it is being formed. This provides a flexible manufacturing process, as it means that strings having different characteristics can be included in the resilient core at any position, in any combination, as it is being formed. The strings could, for example, be delivered directly to the core assembly apparatus from one or more string forming apparatus / stations (not shown). Strings are introduced from string supply stations on opposed sides of the array / core. There may be plural string supply stations on one or both sides of the array. Different string supply stations may be arranged in use to supply stings comprising springs of different type or characteristic, such as (but not limited to) different stiffness . In this way, an array may be built that has different portions or regions, containing springs of different type or characteristic. As an example, an edge portion of the array may contain strings of springs that are of a different characteristic from those of a central or main region of the array. In one preferred example, the edge of the array may comprise springs that are stiffer than those in the main or central portion of the array. In another example, the array may be built up with zones containing strings of springs that are of different characteristic. This can often be desired where a certain portion of the array, or mattress, is to have a stiffer characteristic than another. A further example is where the mattress is to be shared, and the users have different requirements, so that one half of the mattress can be stiffer than the other half. Figure 15 shows a mattress core 2000 made up of a number of strings 2010 of springs in accordance with the earlier described method. The edges of the core 2000 comprise strings 2020 that are of springs of a greater stiffness than the ones used in the rest of the core. This may help to prevent sagging of the core at the edges caused by repeated or prolonged sitting. Figure 16 shows a core 2000 in which a zone Z has strings 2020 that are of stiffer springs than the strings 2010 in the rest of the core. The zone Z may be required to be stiffer as it corresponds to the place where a user places the greatest load on the core during use. Figure 17 shows a core 2000 in which one half of the core is comprised of strings 2010 of springs that are of a different characteristic, such as stiffness for example, than the strings 2020 making up the other half. In this way, a single mattress core can be made that accommodates the different preferences of two people. Using the methods and apparatus of the present invention, a level of versatility is introduced that enables resilient cores to be assembled quickly and reliably, with a variety of different characteristics. The anvils may be retractable from the carriage(s) and / or are arranged for independent movement with respect to the carriage(s). When the machine has a problem or a spring jam occurs, the mattress unit must be removed to clear the problem / spring jam. To aid the removal of the mattress unit it is advantageous to retract the anvils that are trapping the unit in the machine without moving the carriage. Once the mattress unit is removed, and the problem resolved, the retracted anvils may be returned to their original position. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the applicant claims protection in respect of any patentable feature or combination of features referred to herein, and / or shown in the drawings, whether or not particular emphasis has been placed thereon.

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