Background Conventionally, in the manufacture of spring mat- tresses comprising layers of coil springs arranged between the bed frame and the surface of the mattress, the springs are joined together at the spring ends.

Usually springs of the kind known as Bonnell springs are used, wherein neighbouring springs are interconnected in pairs by means of spirals, which are coiled about the adjacent parts of turns in the respective adjacent spring. Thus, the spirals extend in parallel with the surface of the mattress, i. e. across the centre axes of the springs, either in the longitudinal or width direction of the mattress.

This classical mattress does, however, suffer from a number of disadvantages. Since the spirals lock turns in neighbouring springs together rather firmly, the springs fail to be individually resilient. As a result, load on one of the springs of the mattress will cause deflection not only of that spring but also of neighbouring springs.

This is a disadvantage, as it detracts from the adapt- ability of the mattress and because the latter will not distribute the supporting force evenly across the user's entire body surface, and in consequence the mattress is felt as being less comfortable.

In addition, the spirals are wound from metal wire resulting not only in the need for a comparatively complex assembly method but also in a stiff mattress surface that may be felt as bumpy.

Object of the Invention Consequently, one object of the present invention is to provide a spring mattress of the kind defined in the introduction but wherein the disadvantages from which prior-art mattresses of this kind suffer have been com- pletely or at least partly eliminated.

This object is achieved in a spring mattress and by means of a method of manufacturing said mattress as defined in the appended claims.

Brief Description of the Drawings For exemplifying purposes, some embodiments of the invention will be described in the following with reference to the accompanying drawings, wherein: Fig 1 is a lateral view of a part of a spring mat- tress in accordance with one embodiment thereof; Fig 2 is a view from above of the mattress of Fig 1; and Fig 3 is a view from above of a larger part of the spring mattress of Fig 1 as seen from above.

Description of Preferred Embodiments Fig 1 is a lateral view of a portion of a spring mattress comprising springs in accordance with the invention, and Fig 2 is a view from above of that same mattress. The mattress in accordance with the invention comprises a layer of coil springs 1 extending resiliently between the bed frame and the surface of the mattress.

The coil springs 1 are interconnected by strip pieces 2, which are anchored to two turns of adjacent coil springs. The thus interconnected turns of the coil springs preferably are the two end turns of each coil spring. However, it is likewise possible to instead interconnect other turns inside the spring. The turns to be interconnected preferably are larger than the rest of the turns of the spring, i. e. they have a larger radial extension. Owing this larger size, they may be inter-

connected without the other parts of the springs abutting against one another as the springs are exposed to load.

Preferably, springs of the so called double-cone con- figuration are used, i. e. springs the top and bottom turns of which are wider than the rest of the turns, as is the case in conventional Bonnell spring carcasses.

Finally, these turns of the spring, which are intended to be interconnected in accordance with the invention, also preferably are flat, i. e. they extend in a plane that essentially is perpendicular to the centre axis of the spring.

The strip pieces preferably are placed in pairs in such a manner that parts of the turns to be intercon- nected will be sandwiched between the strip pieces, whereupon said strip pieces are joined together by means of gluing or welding. Also preferably, the strip pieces bridge over a number of such pairs of adjacent coil springs.

Preferably, the strip pieces are joined together by means of spot welding. As appears from Fig 2, for each pair of neighbouring springs, two points of attachment 5a and 5b, respectively, are located on the inside of the respective turn of the neighbouring springs, and a further point of attachment 5c is located intermediate the springs. In this manner the strip pieces will grippingly surround the spring wire and hold the springs together. Preferably the spacing between the attachment points is such, however, as to allow the spring wires to move somewhat, i. e. they are able to move slightly relative to one another and to the strip pieces. Owing to this arrangement, the springs are imparted at least some individual resilience, and consequently a spring may be compressed somewhat without affecting neighbouring springs.

It is advantageous to position the strip pieces in succession along lines 6,7,8, which extend in parallel with one another and in parallel with the plane of the

mattress, as appears from Fig 3. Each strip pieces thus preferably joins together several pairs of neighbouring springs, for instance two or three such pairs. In this manner, the springs of the mattress are joined together in all directions and co-operate to absorb pressure exerted on the mattress while at the same time the springs may be compressed comparatively independently of each other. The latter property is desirable both for reasons of comfort and for preventing displacement of the mattress sides, when a load is exerted on the middle region of the mattress.

The feature of dividing the strip pieces in the manner indicated above such that each individual spring is connected only to a small number of other springs is important, above all in the part of the layer that is turned towards the top of the mattress, i. e. in the turn la of the springs of Fig. 1. At the opposite end, on the other hand, such division is uncalled for, since the springs are not to be compressed from this direction. On the contrary, it might even be desirable to refrain from such division, as this contributes to the integrity of the mattress and to its firmness and stability. Prefer- ably, the strip pieces 2a and 2b therefore are divided in the above-mentioned manner whereas the strip pieces 3a and 3b are not.

In addition, the strip piecess could be disposed in staggered relationship in the different lines 6,7,8 in the direction of extension of the individual lines. Thus, as shown in the illustrated embodiment, the strip pieces 6'in line 6 may be positioned in alignment with the strip pieces 8'in line 8, strip pieces 6"in alignment with strip pieces 8"and so on, whereas strip pieces 7' and 7"and so on, positioned in line 7 intermediate lines 6 and 8, may be displaced relative to the elements in lines 6 and 8 by a distance corresponding to one pair of springs. This staggered arrangement improves the

stability and the integrity of the springs in the mattress.

Various joining methods may be used, such as weld- ing, gluing, clamping by means of staples, clips or the like.

The strip pieces may be manufactured from a textile material, preferably of a kind that lends itself to welding. Other materials, such as e. g. plastics materials, are of course also possible.

The spring mattress and the method of manufacturing the same in accordance with the invention offer a number of advantages. The manufacturing process may be simpli- fied, and consequently less expensive, while at the same time a more adaptable and individually resilient and therefore more comfortable mattress is produced.

The invention has been described above by means of one embodiment. Other varieties of the invention are, however, possible. For instance, other types of strip pieces are possible. Instead of strip pieces also short strip pieces or other kinds of surface elements may be used that join together only a couple of springs. It is likewise possible to use one piece of strip, which is attached directly to the spring wire, for instance by means of gluing, instead of, as suggested herein, by means of double strip pieces. It is likewise possible to join together the springs at turns in the interior of the springs instead of at external turns. Such varieties of the invention must be regarded as obvious and to be within the scope of protection of the invention as the latter is defined in the appended claims.