WO2014198816A1 - Apparatus and method for forming a string of pocket springs - Google Patents

Abstract

An apparatus (1) for forming a string (70) of pocket springs comprises a tube forming device (23-25) for forming a tube (50) of pocket material. The apparatus (1) comprises an ultrasonic welding device (30) configured to receive the tube (50) of pocket material and to form a transverse seam which extends between adjacent pockets (71 -74). The apparatus (1) comprises a deflection device (40) configured to deform at least one side portion of the tube (50) of pocket material towards an interior of the tube (50) of pocket material before the ultrasonic welding device (30) forms the transverse seam.

Description

Apparatus and method for forming a string of pocket springs

TECH N ICAL FI ELD

The invention relates to pocket springs. The invention relates in particular to an apparatus and a method for forming a string of pocket springs which comprises a plurality of springs inserted into an associated plurality of pockets, with transverse seams extending between adjacent pockets.

BACKGROUND

Mattresses, sofas or other bedding or seating furniture may be provided with inner- spring units in which the springs are encased in pockets of fabric. Innerspring units which use such pocket springs are generally considered to offer enhanced comfort compared to many conventionally sprung mattresses or other bedding or seating furniture using springs connected by a wire framework. This is partly because pocketed springs may better conform to the shape of a person's body than a mesh of interconnected springs in which the deformation of one spring may more strongly affect the adjacent springs. Also, the presence of the fabric pocket between adjacent springs lessens the likelihood that the springs will rub against each other, thereby reducing noise.

Ultrasonic welding techniques may be used to form a transverse seam between ad- jacent pockets of a string of pocket springs. The transverse seams of a string of pocket springs extend generally perpendicular to the longitudinal direction of the string of pocket springs. The transverse seams are generally parallel to the axes of the pocketed springs. Various drawbacks may be associated with conventional techniques of forming the transverse seams. For illustration, the pockets may have shapes which allow the springs to slightly tilt in the pocket in which they are received . For springs having a small height, there exists a risk that a spring may tilt or even turn in its pocket. This would negatively affect the comfort provided by an innerspring unit in which the string of pocket springs is used. Overlaying material portions may project from the string of pocket springs which may also be undesired because it may give rise to a small degree of unevenness of a top or lower surface of an innerspring unit, which again may negatively affect the comfort provided by an innerspring unit in which the string of pocket springs is used.

SUMMARY

There is a continued need in the art for an apparatus and method for forming a string of pocket springs which mitigates at least some of the drawbacks of conventional techniques. There is also a continued need in the art for a string of pocket springs and for an innerspring unit which mitigates at least some of the drawbacks of conventional pocket springs. There is in particular a need in the art for an apparatus, method and for a product in which the risk of a tilting movement of a spring in its associated pocket may be reduced in a cost-efficient way and/or in which the problems associ- ated with projecting sections of overlaying material are mitigated.

According to embodiments of the invention, a method and apparatus as recited in the independent claims are provided. The dependent claims define preferred or advantageous embodiments of the invention. According to further embodiments of the inven- tion, a string of pocket springs and an innerspring unit are provided in which a pocket includes and recessed section at at least one of its sides against which an end turn of the spring abuts, with a transverse seam providing a fixation for the recessed section.

An apparatus for forming a string of pocket springs comprises a tube forming device for forming a tube of pocket material. The apparatus comprises an ultrasonic welding device configured to receive the tube of pocket material and to form a transverse seam which extends between adjacent pockets. The apparatus comprises a deflection device configured to deform at least one side portion of the tube of pocket material towards an interior of the tube of pocket material before the ultrasonic welding device forms the transverse seam.

The deflection device has the effect that recesses may be formed in at least one side of a pocket against which an end turn of a spring abuts. The inwardly folded material, which forms the recess, is fixed in its position by the ultrasonic welding device because the deflection device folds the material inwardly before the transverse seam is formed. The recesses limit the lateral play of the end turn of the spring, thereby reducing the risk of misalignment. The recesses also reduce or eliminate the amount of overlaying pocket material which projects from the upper and/or lower side of the pocket.

The deflection device may comprise at least one deflector having a projection arranged to push against a side portion of the tube of pocket material. In operation of the apparatus, an end turn of a spring may abut on the side portion of the tube of pocket material at which the pocket material is pushed inward by the at least one deflector.

The deflection device may comprise a first deflector having a projection arranged to push against a side portion and a second deflector having a projection arranged to push against the side portion of the tube of pocket material. The first deflector and the second deflector may be arranged on opposite sides of the ultrasonic welding device. This provides a simple implementation of the deflection device. By using a pair of deflectors which respectively push inward the pocket material on opposite sides of the ultrasonic welding device, overlaying material may be reliably pushed inward while the ultrasonic welding operation is performed. The first and second deflectors are operative to secure the inwardly pushed material during the welding process, even when a spring in an adjacent pocket extends to its rest configuration. The ultrasonic welding device may form the transverse seam which extends across and thereby secures the inwardly pushed pocket material.

The first deflector and the second deflector may be affixed to opposite faces of the ultrasonic welding device. This facilitates installation of the deflection device. The ultrasonic welding device may have a welding surface which extends along a transverse direction. The welding surface may be the welding surface of a sonotrode and/or a surface of an anvil against which the sonotrode pushes the pocket material. The orientation of the welding surface may define the transverse direction along which the transverse seams extend when they are being formed.

The first deflector and the second deflector may be spaced from each other along a longitudinal direction which is orthogonal to the transverse direction.

The deflection device may further comprise a third deflector and a fourth deflector configured to push against another side portion of the tube of pocket material which is opposite to the side portion of the tube of pocket material. In operation of the appa- ratus, the third deflector and the fourth deflector push inward the pocket material at the other side of the tube against which another end turn of the spring abuts. Recesses are formed at the other side of the pocket when the ultrasonic welding device forms the transverse seam which extends across the inwardly pushed pocket material.

The tube forming device may comprise a cassette having a side face which extends in a plane. The deflection device may project across the plane to deform the at least one side portion of the tube of pocket material. This allows recesses to be easily formed by acting on the outer side of the tube of pocket material.

The deflection device may be installed so as to be spaced from the cassette. The deflection device may be installed downstream of the cassette, i.e., a portion of the fabric tube may arrive at the deflection device after it is no longer in abutment with the fabric tube.

The cassette may have another side face parallel to the side face and spaced from the side face by a distance. The deflection device may define a clearance having a width which is less than the distance. This allows recesses to be formed at both axial ends of a pocket.

The apparatus may comprise another ultrasonic welding device configured to form a longitudinal seam. The other ultrasonic welding device may be configured to form the longitudinal seam on a portion of the pocket material which projects from the cassette.

The cassette may be arranged such that the pocket material is guided along an inner side of the cassette. The cassette may have a slit through which longitudinal edges of the pocket material project for forming the longitudinal seam.

The apparatus may comprise a spring insertion device configured to insert springs into the cassette. The spring insertion device may be configured to insert the springs into the cassette such that axial ends of the springs abut against side portions of the tube of pocket material at which the deflection device subsequently folds the pocket material towards the interior of the tube.

The apparatus may comprise a spring forming device configured to form the springs which are inserted into the tube of pocket material. The apparatus may comprise a conveying device to convey the springs from the spring forming device to the spring insertion device. The conveying device may comprise a cooling wheel.

The ultrasonic welding device may comprise a sonotrode and an anvil configured to compress at least four layers of the pocket material between the sonotrode and the anvil when ultrasonic welding is performed.

The ultrasonic welding device may be configured to form the transverse seam such that it extends across two overlaying layers of the pocket material in a central portion of the seam. The ultrasonic welding device may be configured to form the transverse seam such that it extends across at least four overlaying layers of the pocket material in an edge portion of the seam which is adjacent to the central portion, and attaches the at least four layers to each other in the edge portion. The ultrasonic welding device may be configured to form the transverse seam such that it extends across at least four overlaying layers of the pocket material in a first edge portion and in a second end portion of the seam, with the central portion of the seam being interposed between the first and second end portions. The transverse seam may attach the at least four layers to each other in the first end portion and in the second end portion. A method of forming a string of pocket springs according to an embodiment comprises forming a tube of pocket material. The method comprises forming a transverse seam on the tube of pocket material by ultrasonic welding. The method comprises deforming at least one side portion of the tube of pocket material towards an interior of the tube of pocket material before the transverse seam is formed.

The method has the effect that recesses may be formed in at least one axial end of a pocket against which an end turn of a spring abuts. The inwardly deformed material, which forms the recess, is fixed in its position by the ultrasonic welding device. The recesses limit the lateral play of the end turn of the spring, thereby reducing the risk of spring misalignment. The risk of spring misalignment may be particularly relevant for pocket springs for which the height of the spring inserted into its associated pocket is less than the diameter of the spring. The recesses also reduce or eliminate the amount of overlaying pocket material which projects from the end face of the pocket.

At least one deflector may push overlaying material layers of the pocket material towards the interior of the tube of pocket material before the transverse seam is formed. A first and a second deflector arranged on opposite sides of an ultrasonic welding device may push the pocket material towards the interior of the tube for fixation by the ultrasonic welding device.

The transverse seam may be formed such that it comprises a central portion in which two layers of the pocket material are attached to each other, and at least one end portion which extends from the central portion and in which at least four layers of the pocket material are attached to each other.

Other features of methods according to embodiments and the effects attained thereby may correspond to the additional features of the apparatus according to embodiments and the effects attained thereby. The method may comprise inserting springs into the tube of pocket material. The springs may respectively have a first end turn, an opposite second end turn, and at most 2 active turns between the first end turn and the second end turn. The method and apparatus may in particular be used for forming a string of pocket springs having low pocket springs.

The springs may have a height which is between 25 mm and 40 mm when the springs are inserted into the pockets. The method may be performed by the apparatus according to an aspect or embodiment.

A plurality of strings of pocket springs may be formed in the manner described above. To form an innerspring unit, the plurality of strings of pocket springs may be attached to each other to form the innerspring unit.

The innerspring unit may be an innerspring unit for a mattress, an innerspring unit for a sofa, an innerspring unit for an armchair or for another bedding or seating furniture. According to another embodiment, a string of pocket springs is provided. The string comprises a plurality of springs and a plurality of pockets. Each spring is received in respectively one of the pockets. A transverse seam is formed between two adjacent pockets of the string. The transverse seam has a first portion which attaches at least two layers of pocket material to each other. The transverse seam has a second por- tion which attaches at least four layers of pocket material to each other.

In a string of pocket springs having such a configuration, the second portion of the transverse seam provides a fixation for inwardly folded overlaying portion of the pocket material. This forms a recess in an axial end face of the pocket against which an end turn of a spring abuts. The transverse seam may have a third portion which attaches at least four layers of pocket material to each other. The first portion may be interposed between the second portion and the third portion. A pocket of the string of pocket springs may have first and second end faces which are transverse to an axis of a spring received in the pocket. At least one recess may be formed by inwardly folded pocket material in at least one of the first and second end faces. Two recesses may be formed by inwardly folded pocket material in at least one of the first and second end faces. Two recesses may be formed by inwardly folded pocket material in the first end face, and two other recesses may be formed by inwardly folded pocket material in the second end face.

An innerspring unit according to an embodiment comprises a plurality of strings of pocket springs according to an embodiment, which are attached to each other to form a two-dimensional array of pocket springs.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described in detail with reference to the draw- ings in which like reference numerals designate like elements.

Fig. 1 shows a schematic side view of an apparatus according to an embodiment.

Fig. 2 shows a plan view of an apparatus according to an embodiment.

Fig. 3 shows a perspective view of a pocket material processed in an apparatus according to an embodiment in combination with components of the apparatus.

Fig. 4 is a cross-sectional view of a tube of pocket material formed by a tube forming device of an apparatus according to an embodiment.

Fig. 5 is a cross-sectional view of a tube of pocket material when a deformation device of an apparatus according to an embodiment deforms at least one side portion. Fig. 6 is a cross-sectional view of a tube of pocket material with deformed side portions when sandwiched by an ultrasonic welding device of an apparatus according to an embodiment.

Fig. 7 shows a side view of a string of pocket springs produced using an apparatus or method according to an embodiment.

Fig. 8 shows a side view of a string of pocket springs produced using a conventional technique.

Fig. 9 is a cross-sectional view through a pocket along lines IX-IX in Fig. 7. Fig. 10 is a plan view of an axial end of a pocket of the string of Fig. 7.

Fig. 1 1 is a perspective partial view of an apparatus according to an embodiment.

Fig. 12 is an exploded detail view of components of an apparatus according to an embodiment.

Fig. 13 and Fig. 14 are perspective detail views of a deflector which may be used in the apparatus of Fig. 12.

Fig. 15 is a cross-sectional view of the deflector of Fig. 13 and Fig. 14.

DESCRIPTION OF EMBODIMENTS

Fig. 1 illustrates an apparatus 1 for forming a string 70 of pocket springs 71 -74 according to an embodiment.

The apparatus 1 generally comprises a device for forming a tube 50 of pocket material. The device for forming a tube of pocket material may comprise a cassette 25, for example. The cassette 25 may be arranged to form the tube 50 of pocket material at its inner side. Pocket material may be fed to the device for forming a tube 50 of pocket material as a continuous band 22. The pocket material may be fed from a supply 21 , e.g. a roll of pocket material. One or several folding device(s) 24 may be used to deflect and/or fold the pocket material such that it is transported through the cassette 25 as a tube of pocket material. The apparatus 1 may comprise a motor 23 to feed the pocket material to the cassette 25 and/or to discharge the pocket material from the supply 21 by rotating the roll of pocket material.

The tube 50 of pocket material may have a pair of sides against which the end turns of a spring 9 abut. When the string 70 of pocket springs 71 -74 is installed in an inner- spring unit, these sides against which the end turns of the spring 9 abut define the upper and lower side of the innerspring unit. The tube 50 of pocket material may have another pair of sides which extends between sides against which the end turns of the spring 9 abut. As will be explained in more detail with reference to Fig. 2 to Fig. 15, the apparatus 1 is configured such that recesses are formed in at least one side portion of a pocket against which an end turn of the spring abuts. The recesses are formed by inwardly deforming the corresponding side portion of the tube 50 before a transverse seam is formed. The ultrasonic welding operation which forms the transverse seam secures the inwardly folded pocket material so as to form the recess.

The tube 50 of pocket material has a longitudinal direction 3 which corresponds to a longitudinal axis of the cassette 25. The tube 50 of pocket material is advanced through the cassette 25 along the longitudinal direction 3. Springs 9 is inserted into the cassette 25 such that the springs 9 are at least partially enclosed by the tube 50 of pocket material. The longitudinal edges of the band of pocket material may be attached to each other while the pocket material is advanced through the cassette. An ultrasonic welding device 39 may be provided to form the longitudinal seam which attaches the opposite longitudinal edges of the pocket material to each other, so as to form a closed tube 50 of pocket material. When the tube 50 is formed along the inner side of the cassette 25, the longitudinal edges of the band of pocket material may project through a slit of the cassette 25 and may be attached to one another using another ultrasonic welding device 39. The apparatus 1 may comprise a spring feeding device 10 which provides the springs 9 for insertion into the tube 25. The spring feeding device 10 may comprise a spring forming device which forms the springs 9 from a wire. The spring feeding device 10 may comprise a conveying device to convey the springs from the spring form- ing device to the cassette 25. The conveying device may comprise a cooling wheel. An insertion device 8 may insert the springs into the cassette 25. The insertion device 8 may comprise a lever or a pair of levers or a pivotable transfer device.

The apparatus 1 comprises an ultrasonic welding device 30 configured to form a transverse seam between adjacent pockets. The ultrasonic welding device may comprise a sonotrode 31 and an anvil 32. The ultrasonic welding device 30 is arranged to receive the tube 50 of pocket material with the springs arranged therein. The ultrasonic welding device 30 is configured to form a transverse seam between adjacent pockets 71 -74. The ultrasonic welding device 30 defines a transverse direc- tion 4 (shown in Fig. 2 and Fig. 3) along which the transverse seam extends when it is being formed. The transverse direction 4 may be defined by an ultrasonic welding surface of the ultrasonic welding device 30. The transverse direction 4 extends perpendicular to the longitudinal direction 3 of the tube 50. The apparatus 1 comprises a deflection device 40. As will be explained in more detail with reference to Fig. 2 to Fig. 15, the deflection device 40 is configured to push inward the pocket material at at least one side of the tube 50. Inwardly folded material sections may thereby be formed at at least one of the sides of the tube 50 which are oriented perpendicularly to the transverse direction 4. The deflection device 40 may comprise at least one deflector which is operative to push the pocket material at at least one side of the tube 50 towards the interior of the tube 50 before ultrasonic welding is performed. This inwardly folded section of pocket material is secured in its inwardly-folded configuration at the transverse seam when ultrasonic welding is performed.

The apparatus 1 may comprise a controller 2 which controls operation of the apparatus 1 . The controller 2 may be configured to control operation of the motor 23, of the spring insertion device 8, of the spring feedings device 10 and/or of the ultrasonic welding device 30.

The operation and configuration of the deflection device 40 of an apparatus accord- ing to embodiments will be explained in more detail with reference to Fig. 2 to Fig. 15.

Fig. 2 is a schematic plan view of an apparatus 1 according to an embodiment. The deflection device 40 comprises a first deflector 41 and a second deflector 42. The first deflector 41 and the second deflector 42 are operative to inwardly deform a side portion of the tube which abuts on a lateral side 26 of the cassette 25. The lateral side 26 is perpendicular to the transverse direction 4 along which the transverse seam is formed by the sonotrode 31 . The lateral side 26 of the cassette 25 may extend in a plane 28. The first deflector 41 and the second deflector 42 may respectively project beyond the plane 28 towards the interior of the tube 50. The first deflector 41 and the second deflector 42 may thereby deform a side portion of the tube 50 against which an end turn of a spring 9 abuts. The first deflector 41 and the second deflector 42 may fold inward a portion of this side portion of the tube 50 for the ultrasonic welding process in which the transverse seam 55 is formed.

The first deflector 41 and the second deflector 42 may be arranged on opposite sides of the ultrasonic welding device 30 which forms the transverse seams. For illustra- tion, the first deflector 41 may be interposed between the ultrasonic welding device 30 and the cassette 25. The second deflector 42 may be arranged on a side of the ultrasonic welding device 30 which faces away from the cassette 25. The second deflector 42 may be operative to prevent the inwardly-deformed side portion of the tube 50 to be drawn in an outward direction by a force applied by a spring in an adjacent pocket. The first deflector 41 and the second deflector 42 may be offset from each other along the longitudinal direction 3 which is orthogonal to the transverse direction 4. The deflection device 40 may optionally comprise a third deflector 43 and a fourth deflector 44. The third deflector 43 and the fourth deflector 44 may be used when it is desired to form recesses on both axial end faces of a pocket. If such recesses are only to be formed on one axial end face of the pocket, the third deflector 43 and the fourth deflector 44 may also be omitted.

The third deflector 43 and the fourth deflector 44 may respectively project beyond a plane 29 in which another lateral side 27 of the cassette 25 is arranged. The lateral side 26 and the other lateral side 27 of the cassette may be parallel to each other. The operation and configuration of the third deflector 43 and the fourth deflector 44 may correspond to the operation and configuration of the first deflector 41 and the second deflector 42 described above.

The lateral side 26 and the other lateral side 27 are spaced by a distance. The dis- tance defines a height of the tube 50, measured parallel to the axes of the springs, while the tube 50 is being guided along the cassette 25. The deformation device 40 defines a clearance between the first deflector 41 and the opposing third deflector 43. The clearance may be smaller than the distance between the lateral side 26 and the other lateral side 27 of the cassette 25. This causes an inward deformation of at least one of the side portions of the tube 50 as it is transported along the deflection device 40.

Fig. 3 illustrates the process of forming pockets of a string of pocket springs in an apparatus according to an embodiment. The pocket material is fed as a band 22 of pocket material. The pocket material has a first side 51 , which forms an outer side of the pockets, and a second side 52 which forms an inner side of the pockets. The second side 52 is shown in hatched style in Fig. 3.

The band 22 of pocket material may be folded by the folding device 24, with the sec- ond side 52 being arranged at the outer sides of the folded band. The folded band may be transported to an entrance of the cassette 25. The cassette 25 is omitted in Fig. 3 for clarity. In an entrance area 53 of the cassette 25, the folded band 22 of pocket material is drawn into the cassette 25 in such a way that the first side 51 abuts on the inner faces of the cassette 25. The longitudinal edges of the band 22 may project from the cassette 25. A longitudinal welded seam 54 may be formed along the longitudinal edges of the band 22 to form a closed tube 50. Springs 9 are inserted into the tube 50 at the entrance area 53 of the cassette 25. An end turn of each spring 9 respectively abuts on a side portion 56 of the tube 50.

The deformation device 40 deforms the side portion 56 before the welding device 30 forms the transverse seam 55. The deformation device 40 may push the pocket material towards the interior of the tube at the side portion 56, thereby forming a recess 61 in the side portion. The recess 61 may be formed locally, so as to extend between a line which connects the axial centers of adjacent springs. The ultrasonic welding device 30 forms the transverse seam so that it extends across the inwardly-deformed overlaying pocket material, which secures the inwardly-deformed material at the transverse seam 55.

Fig. 4 to Fig. 6 show cross-sectional views of the tube of pocket material.

Fig. 4 shows a cross-sectional view of the tube 50 of pocket material at an end of the cassette 25 which faces towards the ultrasonic welding device 30. The tube 50 has a side portion 56 and an opposite side portion 57. Springs are inserted into the tube 50 such that a first end turn abuts on the side portion 56 and that an opposite second end turn abuts on the other side portion 57. The side portions 56, 57 of the tube 50 define the upper and lower axial end faces of the pockets in the string of pocket springs when an inner spring unit is in use. The connecting sides 58, 59 extend transverse to the side portions 56, 57. The connecting sides 58, 59 extend generally parallel to the axis of a spring inserted into the tube 50.

Fig. 5 shows a cross-sectional view 60 of the tube of pocket material at the location at which the ultrasonic welding device 30 acts on the tube of pocket material. A first inwardly-deformed section 61 is formed at the side portion 56. A second inwardly- deformed section 62 may optionally be formed at the other side portion 57. The first inwardly-deformed section 61 and the second inwardly-deformed section 62 are formed by the deformation device 40. The first inwardly-deformed section 61 and the second inwardly-deformed section 62 respectively include a section of overlaying material which is pushed towards the interior of the tube. The first inwardly-deformed section 61 and/or the second inwardly-deformed section 62 may respectively comprise a concavity formed in the at least one side portion of the tube.

Fig. 6 shows a cross-sectional view 63 of the tube of pocket material when the tube is being compressed between the anvil 32 and the sonotrode 31 for forming the transverse seam. The inwardly-deformed section 61 is fixed in its position at the seam. In an end region 64 of the transverse seam, four layers of the pocket material are attached to each other by the transverse seam. Similarly, the inwardly-deformed section 62 is fixed in its position at the transverse seam. In an opposite end region 65 of the transverse seam, four layers of the pocket material are attached to each other by the transverse seam. The transverse seam may have a central portion at which the transverse seam only attaches two layers of pocket material to one another. In other embodiments, the number of layers of pocket material may be greater than two in the central portion of the transverse seam. For illustration, for pocket springs having a small spring height, at least four layers of pocket material may be attached to each other throughout the transverse seam. For further illustration, overlaying material layers which result from the welding of the longitudinal seam may also have the effect that four layers of pocket material are attached to each other in a central portion of the transverse seam. More complex configurations may be used for inwardly deforming at least one side portion of the tube 50. For illustration, while a single inward bulge 61 at the side portion 56 is illustrated in Fig. 5 and Fig. 6, two or more than two inward bulges may be formed at the side portion 56 which may be spaced from each other in a direction orthogonal to the transverse direction. Accordingly, more than four layer of the pocket material may be attached to each other at an edge portion of the transverse seam. Similarly, while a single inward bulge 62 at the other side portion 57 is illustrated in Fig. 5 and Fig. 6, two or more than two inward bulges may be formed at the other side portion 57. Fig. 7 is a side view of a string 70 of pocket springs. The string 70 comprises a plurality of pockets 71 -74. A spring is received in each one of the pockets 71 -74. The springs in pockets 72, 73 are shown with broken lines for illustration. The pockets are delimited by transverse seams 75, 76, 77. A pocket 72 is delimited from its adjacent pockets 71 , 73 by transverse seams 75, 76.

Because a side portion of the tube 50 is pushed towards the interior of the tube 50 and is secured there at the transverse seam 75, 76 when the transverse seam 75, 76 is formed, the pocket 72 has recesses 78 at the upper axial end face on which an end turn of the spring abuts. The recesses 78 extend from the transverse seams 75, 76. The upper side of the pocket 72 may bulge at a central area between the recesses 78 where the upper end turn of the spring abuts. Alternatively or additionally, the pocket 72 may have recesses 79 at the lower side on which another end turn of the spring abuts. The recesses 79 extend from the transverse seams 75, 76. The lower side of the pocket 72 may bulge at a central area between the recesses 79 where the lower end turn of the spring abuts. Each one of the various pockets 71 -74 of the spring may have the same configuration as explained for pocket 72.

The number of layers of pocket material that are attached to each other may vary along a transverse seam 75-77. For illustration, each transverse seam may have a first portion 67 at which the transverse seam attaches at least two layers of pocket material to each other. The transverse seam may have at least one second portion 68, 69 adjacent to the first portion 67. In the second portion 68, 69, four or more than four layers of the pocket material may be overlaid on each other and may be attached to each other by the transverse seam. As illustrated in Fig. 7, the two end por- tions 68, 69 of the transverse seam which extend from the ends of the transverse seam may respectively attach at least four layers of the pocket material to each other. The first portion 67 may be a central portion of the transverse seam which is interposed between the two end portions 68 and 69.

Two layers of pocket material may be attached to each other by the transverse seam at the first portion 67. More than two layers of pocket material, e.g. four layers of pocket material, may be attached to each other by the transverse seam at the first portion 67.

The recesses 78, 79 formed at the boundaries between adjacent pockets are in con- trast to conventional strings of pocket springs in which the ends of the transverse seams project from the upper and lower axial faces of the pockets of the string, respectively. Fig. 8 illustrates a conventional string 80 of pocket springs which is not an embodiment of the present invention. The string 80 has a plurality of pockets 81 -84. A spring is received in each one of the pockets 81-84. The springs in pockets 82, 83 are shown in broken lines for illustration. Adjacent pockets are delimited by transverse seams 85, 86, and 87. The transverse seams 85, 86, 87 respectively terminate at a projection 88, 89 at both the upper side and the lower side of the string 80. By contrast, as illustrated in Fig. 7, the transverse seams 75, 76, 77 terminate in a recess at the upper side and/or at the lower side of a string of pocket springs when us- ing techniques according to embodiments of the invention.

Fig. 9 illustrates a cross-section through a pocket 72 of a string of pocket springs 70 formed in accordance with an embodiment. The cross-section of Fig. 9 is taken in a plane which is spaced from a transverse seam 75, but extends parallel to the trans- verse seam. The corresponding location is indicated by lines IX-IX in Fig. 7. As shown in Fig. 9, the recess 78 extends from the transverse seam 75 towards the interior of the upper side of the pocket. A width and/or depth of the recess 78 may vary as a function of distance from the transverse seam 75. For illustration, the recess 78 may have a depth which decreases with increasing distance from the transverse seam 75.

Fig. 10 is a plan view of an upper axial end face of the pocket 72. The upper side of the pocket 72 has recesses 78 which extend from the transverse seams 75, 76. A lateral width of the recesses 78 may respectively increase with increasing distance from the transverse seam 75, 76. A depth of the recesses 78 may respectively decrease with increasing distance from the transverse seam 75, 76. The inwardly folded overlaying material which defines the recesses 78, 79 at the upper side and/or lower side of a pocket reduces the play of a spring received in the respective pocket. The risk of a spring tilting or turning in its associated pocket may be reduced. This is of particular relevance for springs having a low height. For illustration, the springs inserted into the pockets of the string 70 may have a spiral body which extends from a first end turn to the second end turn of the spring. The spiral body may consist of at most 2 active turns. The spiral body may consist of at least 1 active turns.

The springs may have a height of less than 100 mm, when in an unloaded condition. The springs may have a height of at least 40 mm and less than 100 mm, when in an unloaded condition. The springs may have a height which may be less than 40 mm. The springs inserted into the pockets may have a height which is between 25 mm and 40 mm. A diameter of each spring, measured at the turn having maximum diameter, may be equal to or greater than the height of the spring when the spring is inserted into its associated pocket. However, the techniques disclosed herein may also be used for springs having a greater number of turns and/or for springs having greater heights. As can be seen by comparison of Fig. 7 and Fig. 8, the inwardly folded overlaying material which defines the recesses 78, 79 at the upper side and/or lower side of a pocket reduces projections of the pocket material. This mitigates the drawbacks associated with the projections at the welded seams in conventional strings of pocket springs.

The deflection device which inwardly deforms at least one side portion of the tube 50 before ultrasonic welding is performed may have any one of a variety of different configurations. For illustration, the deflection device may comprise at least one deflector which is mounted separately from the ultrasonic welding device and the tube forming device. In other embodiments, the deflection device may comprise at least one deflector which is mounted to the ultrasonic welding device or the tube forming device, as will be explained in more detail with reference to Fig. 1 1 and Fig. 12.

Fig. 1 1 is a perspective view of an ultrasonic welding device 30 and a deflection device of an apparatus according to an embodiment. Fig. 12 is an exploded view of the ultrasonic welding device 30 and the deflection device of the apparatus according to an embodiment.

The ultrasonic welding device 30 comprises a sonotrode 31 and an anvil 32. The sonotrode 31 has an ultrasonic welding surface 33. The welding surface 33 and anvil 32 define the transverse direction along which the transverse seam is formed. The ultrasonic welding device 30 has a carrier 34. In the implementation shown in Fig. 1 1 and Fig. 12, the anvil 32 is mounted to the carrier 34.

At least one deflector of the deflection device is mounted to the ultrasonic welding device 30. A first deflector 41 and a second deflector 42 may be mounted to opposite faces of the ultrasonic welding device 30. Similarly, a third deflector 43 and a fourth deflector 44 may be mounted to opposite faces of the ultrasonic welding device 30.

Referring to Fig. 12, a first support 81 may be secured to a first side of the ultrasonic welding device 30. A second support 82 may be secured to a second side of the ultrasonic welding device 30. Any one of various mechanical connections may be used for attaching the first and second supports 81 , 82 to the carrier 34. For illustration, bolts 83, rivets, or other connectors may be used to secure the first and second supports 81 , 82 to the carrier 34.

The first deflector 41 may be secured to the first support 81 . The second deflector 42 may be secured to the second support 82. The first deflector 41 and the second deflector 42 may have identical designs. The first deflector 41 and the second deflector 42 may be arranged so as to be mirror-symmetric relative to a plane in which the anvil 32 extends. The third deflector 43 may be secured to the first support 81 . The fourth deflector 44 may be secured to the second support 82, The third deflector 43 and the fourth deflector 44 may have identical designs. The third deflector 43 and the fourth deflector 44 may be mounted so as to be mirror-symmetric relative to the plane in which the anvil 32 extends.

Any one of various mechanical connections may be used for attaching the deflectors to the supports. For illustration, a bolt 85 and washer 84, a rivet, or other connectors may be employed to secure the deflectors to the supports. The bolt 85 may engage a mating nut in the support 81 , 82.

At least some of the deflectors 41-44 may be configured in such a way that the spacing between the first deflector 41 and the third deflector 43 and the spacing between the second deflector 42 and the fourth deflector 44 may be adjusted. For illustration, at least some of the deflectors 41 -44 may have a slit 47 for passing the bolt 85 or other connector through the slit 47. The slit 47 may extend parallel to the welding surface 33 when the respective deflector is mounted. This allows the position of the deflector to be adjusted in the transverse direction.

The various deflectors 41 -44 may respectively have identical configurations. This allows the deflection device to be constructed with a small number of components having different configurations. To this end, the deflectors of the deflection device may respectively be designed such that they have a mirror-symmetric configuration rela- tive to a center plane. The center plane may extend perpendicular to the welding surface 33 when the deflector is installed in the apparatus.

Fig. 13 and Fig. 14 show perspective views of a deflector 41 which may be used in an apparatus according to an embodiment. Each one of the deflectors 41 -44 may have the configuration illustrated in Fig. 13 and Fig. 14.

The deflector 41 has a slit 47 through which a connector may be passed for securing the deflector 41 to the support 81 , 82. The deflector 41 has a recess 48 in which the support 81 , 82 may be received. The deflector has a first projection 45 and a second projection 46. The first projection 45 and the second projection 46 may be mirror- symmetric relative to each other. Depending on where the deflector 41 is mounted on the support 81 , either the first projection 45 or the second projection 46 will be opera- tive to deform a side portion of a tube 50 of pocket material.

The first projection 45 and the second projection 46 may respectively include a slanted face 49 along which the pocket material slides when the tube 50 of pocket material passes the deflector 41 . The slanted face 49 may be configured such that it does not have a sharp edge at a location which comes into contact with the tube 50 of pocket material.

Fig. 15 is a partial cross-sectional view through a deflector 41 , illustrating a projection 45 of the deflector 41 in a plane which is parallel to the welding surface 33 and or- thogonal to the longitudinal direction of the tube 50. The projection 45 is operative to deform a side portion of the tube 50 of pocket material when the tube 50 is guided past the deflector 41 . Each one of the deflectors 41 -44 may have the configuration illustrated in Fig. 15. The projection includes a straight portion 90. In operation of the apparatus, the straight portion 90 may be arranged such that a center axis of a spring inserted into the tube 50 of pocket material is moved along the straight portion 90 when the tube 50 is moved past the deflector 41 . At an upper and lower end of the straight portion 90, there are rounded portions 91 , 92 to reduce the risk of the pocket material being damaged.

While embodiments of the invention have been described with reference to the drawings, a wide variety of modifications may be implemented in other embodiments. For illustration, the deflection device does not need to be composed of deflectors that are all secured to the ultrasonic welding device. The deflectors of the deflection device may have configurations which are different from one another. For illustration, each deflector may have a projection on only one side to inwardly deform a side portion of a tube of pocket material. While embodiments have been described in which recesses are formed both in the upper axial end face of a pocket and the lower axial end face of the pocket, the recesses may be formed only in the upper axial end face or only in the lower axial end face of a pocket in other embodiments. Accordingly, the deflection device may be configured to inwardly deform only one of the two side portions of the tube of pocket material.

The apparatuses, methods, and products according to embodiments of the invention may be used for manufacturing innerspring units for mattresses, sofas, armchairs, or other bedding or seating furniture, without being limited thereto.

Claims

1 . An apparatus for forming a string (70) of pocket springs, the apparatus (1 ) comprising:

a tube forming device (23-25) for forming a tube (50) of pocket material;

an ultrasonic welding device (30) configured to receive the tube (50) of pocket material and to form a transverse seam (55; 75-77) which extends between adjacent pockets (71 -74); and

a deflection device (40) configured to deform at least one side portion (56, 57) of the tube (50) of pocket material towards an interior of the tube (50) of pocket material before the ultrasonic welding device (30) forms the transverse seam (55; 75-77).

2. The apparatus according to claim 1 ,

wherein the deflection device (40) comprises at least one deflector (41 -44) having a projection arranged to push against a side portion (56) of the tube (50) of pocket material.

3. The apparatus according to claim 2,

wherein the at least one deflector (41-44) comprises a first deflector (41 ) hav- ing a projection (45) arranged to push against the side portion (56) and a second deflector (42) having a projection (45) arranged to push against the side portion (56), wherein the first deflector (41 ) and the second deflector (42) are arranged on opposite sides of the ultrasonic welding device (30).

4 The apparatus according to claim 3,

wherein the first deflector (41 ) and the second deflector (42) are affixed to opposite faces of the ultrasonic welding device (30).

5. The apparatus according to claim 3 or claim 4,

wherein the ultrasonic welding device (30) has a welding surface (33) extending along a transverse direction (4), and wherein the first deflector (41 ) and the second deflector (42) are spaced from each other along a longitudinal direction (3) which is orthogonal to the transverse direction (4).

6. The apparatus according to any one of claims 3 to 5,

wherein the deflection device (40) further comprises a third deflector (43) and a fourth deflector (44) configured to push against another side portion (57) of the tube (50) of pocket material which is opposite to the side portion (56) of the tube (50) of pocket material.

7. The apparatus according to any one of the preceding claims,

wherein the tube forming device (23-25) comprises a cassette (25) having a side face (26) which extends in a plane (28), and

wherein the deflection device (40) projects across the plane (28) to deform the at least one side portion (56) of the tube (50) of pocket material.

8. The apparatus according to claim 7,

wherein the cassette has another side face (27) parallel to the side face (26) and spaced from the side face (26) by a distance,

wherein the deflection device (40) defines a clearance having a width which is less than the distance.

9. The apparatus according to any one of the preceding claims,

wherein the ultrasonic welding device (30) comprises a sonotrode (31 ) and an anvil (32) configured to compress at least four layers of the pocket material between the sonotrode (31 ) and the anvil (32) when ultrasonic welding is performed.

10. A method of forming a string (70) of pocket springs, the method comprising: forming a tube (50) of pocket material;

forming a transverse seam (55; 75-77) on the tube (50) of pocket material by ultrasonic welding; and deforming at least one side portion (56, 57) of the tube (50) of pocket material towards an interior of the tube (50) of pocket material before the transverse seam (55; 75-77) is formed.

1 1 . The method according to claim 10,

wherein at least one deflector (41 -44) pushes overlaying material layers of the pocket material towards the interior of the tube (50) of pocket material before the transverse seam (55; 75-77) is formed.

12. The method according to claim 10 or claim 11 ,

wherein the transverse seam (55; 75-77) comprises

a central portion (67) in which at least two layers of the pocket material are attached to each other, and

at least one end portion (68, 69) which extends from the central portion to an end of the transverse seam (55; 75-77) and in which at least four layers of the pocket material are attached to each other.

13. The method according to any one of claims 10 to 12,

wherein springs (9) are inserted into the tube (50) of pocket material, and wherein the transverse seam (55; 75-77) and a longitudinal seam (54) are formed to encase a spring (9) of the springs (9) in an associated pocket (71-74), wherein a height of the spring (9) encased in its associated pocket (71 -74) is equal to or less than a diameter of the spring (9) measured at a turn of the spring (9) having maximum diameter.

14. The method according to any one of claims 10 to 13,

which is performed by the apparatus (1 ) according to any one of claims 1 to 9.

15. A method of forming an innerspring unit, comprising:

forming a plurality of strings (70) of pocket springs by the method according to any one of claims 10 to 14, and

attaching the plurality of strings (70) of pocket springs to each other to form the innerspring unit.