Source: {"pile_set_name": "USPTO Backgrounds"}

Interior spring mattresses consist of a multitude of steel springs joined together in a regular grid. Typically, the end rings of the neighboring steel springs are directly connected to one another by way of wire spirals. Alternatively, barrel shaped springs are often sewn or welded into pockets in rows and in turn the pockets lying next to one another are connected to one another. With inexpensive mattresses, all the springs used are designed to be identical, i.e. they have the same spring constants and the mattress is uniformly hard or soft over the whole surface. In order to achieve a greater sleeping comfort there is the desire to design the mattress with different hard or soft zones, in particular to reinforce the heavily loaded zones. The differing hardnesses in the individual mattress regions have up to now been produced in different ways. For example, geometrically identical springs with differing wire strengths may be manufactured and used, in which springs with thicker wires are applied in the regions of greater firmness, e.g. in the central region, and springs with thinner wires are applied in regions that are softer, e.g. in the region of the head or feet. The manufacture of springs of different thicknesses does not present a problem in itself, but on later assembly of the mattress, these springs must be arranged at the correct locations in the spring interior. This is not possible with fully automatically operating machines of the present art since typically springs of different types are usually alternately transferred from the winding machine and inserted into the automatic assembly machine. The springs are laid behind one another in rows and the rows one after the another are connected to each other by wire spirals.
Another possibility of producing various hardness regions within a mattress lies in arranging the springs to lie closer to one another in the region of desired reinforcement. Then, the grid in which the springs are then arranged in the spring interior will no longer be uniform. Two springs may also directly inserted one into another.
The manufacture of a mattress with a non-uniform spring grid as well as also the manufacture of a mattress with springs of differing wire strengths is only possible by way of large scale conversions of conventional machines. In one case, the setup of the assembly machine must be changed, which leads to stoppage time and thus to higher manufacturing costs; in another case, two automatic spring winding machines would be necessary, but differing springs could only be arranged in rows.
Accordingly, there remains a need for a better way of providing spring interiors with regions of differing firmness.