Apparatus and method for making a resilient unit
Apparatus for forming a resilient unit comprises a conveyor ( 210 ) and first and second spring supply stations ( 212 and 214 ), arranged in use to deposit respectively first and second spring types ( 216 and 218 ) under compression onto the conveyor. The conveyor is arranged in use to convey a row of the springs ( 216, 218 ) in a direction shown by Arrows A 4 towards pocketing station ( 220 ). At the pocketing station ( 220 ) the springs are urged from the conveyor into positions between upper and lower sheets ( 222 and 224 ), by a plurality of inserter devices ( 226 ) that move together in a reciprocating fashion in the direction of arrow A 5 , before retracting to the position shown. After each row of springs is inserted between the sheets ( 222 ), upper and lower computer-controlled welding tools (not shown) come together at positions P between the springs to join the sheets together, forming pockets in which the springs are encased. After each welding event the resilient unit is indexed forwards a distance equal to one pocket width in the direction of Arrows A 6 by computer-controlled drive means (not shown). The next row of springs is then conveyed into position ready for insertion between the sheets of material, and the process is repeated. The two spring supply stations are arranged to supply springs that differ from one another in at least one characteristic.
1. A resilient unit, comprising:
a plurality of spring pairs, wherein:
each spring pair includes an inner spring positioned inside of an outer spring;
for each spring pair, the inner spring is taller than the outer spring;
an array of discrete pockets, wherein each pocket of the array of pockets includes a spring pair of the plurality of spring pairs that is entirely located within the pocket;
a first contiguous sheet of material and a second contiguous sheet of material directly joined together to form the array of discrete pockets, such that each pocket of the array of pockets is bounded by the first sheet and the second sheet
wherein, for each pocket of the array of pockets, when no external forces are applied to the pocket, the first sheet and the second sheet compresses the spring pair included in the pocket and hold the inner spring away from the outer spring so as to prevent contact between the inner spring and the outer spring.
2. The resilient unit according to claim 1 , wherein the second spring is substantially held in position by the pocket of the first spring.
3. The resilient unit according to claim 1 , wherein the first spring is wider than it is tall.
4. The resilient unit according to claim 1 , wherein the second spring is taller than it is wide.
5. The resilient unit according to claim 1 , wherein the first springs are of wire of a first gauge and the second springs are of wire of as second, different gauge.
6. The resilient unit according to claim 5 , wherein the first gauge is greater than the second gauge.