Field of the Invention The present invention relates to a spring mattress comprising springs enclosed in casings, a so-called pocket spring mattress, as well as a method and a device for manufacturing such a mattress.

Background Art A common technique of making spring mattresses is the so-called pocket technique. This means that the springs are enclosed in pockets, i. e. they are indivi- dually enclosed by a casing material. In this way, the springs will be relatively individually resilient so that they can flex individually without affecting the neighbouring springs and, thus, the comfort to the user increases since his weight will thus be distributed more uniformly over the surface that receives the load.

A drawback of such mattresses is, however, that it is difficult to make thin mattresses. If the length of the springs is reduced without a corresponding reduction of the width, the spring will, especially when the length approaches the length of the diameter of the spring, have a tendency to turn in the casing, which dramatically deteriorates the comfort of the mattress. When such mat- tresses are to be manufactured, the existing technique requires a much larger number of springs. Consequently the manufacture will be considerably more expensive and more complicated. Besides it is difficult to prevent such mattresses from also being stiffer since too thin spring wire cannot be used.

For these reasons, it has not been possible to use spring mattresses for many purposes where thinner mat- tresses are required, such as for bed mattresses, seat cushions and the like. In spite of this, spring mat- tresses have several properties making it desirable to

use them also in these contexts, such as excellent com- fort, individual flexibility, a long life and easy and inexpensive manufacture.

Object of the Invention It is therefore an object of the present invention to provide a spring mattress of the type mentioned by way of introduction, as well as a method and a device for manufacturing the same, in which the above drawbacks are obviated wholly or at least partly.

This object is achieved by a spring mattress and a method for manufacturing the same according to the appended claims.

Brief Description of the Drainas In the accompanying drawings Fig. 1 illustrates a device for manufacturing a mat- tress according to an embodiment of the invention; Fig. 2 illustrates a mattress according to an embo- diment of the invention; Fig. 3 is a schematic sectional view of the device in Fig. 1 from above; Fig. 4a is a schematic sectional view of the device in Fig. 1, seen from the side, the inserting means being inserted past the abutment member; and Fig. 4a is a schematic sectional side view of a finished spring element according to the invention.

Description of the Preferred Embodiments For the purpose of exemplification, the invention will now be described in more detail by way of an embo- diment and with reference to the accompanying drawings.

A spring mattress according to the invention com- prises a plurality of interconnected coil springs 1 enclosed in casings 2. The casing is suitably made of a, preferably weldable, textile material, but also other materials such as different types of plastic materials

can be used. It is also possible to use non-weldable tex- tile materials, such as cotton cloth. Such mattresses, so-called pocket spring mattresses, are previously known, and the manufacture thereof is not part of the present invention. Normally, strings of interconnected coil springs in casings are manufactured automatically, where- upon these strings are cut in suitable lengths and joined side by side to form mattresses.

According to the invention, for at least one of the springs, the casing portions arranged at the spring ends are moved towards each other, through the spring, and interconnected with the aid of connecting means to pro- vide at least a certain degree of bias. Preferably, the casing portions are moved so far towards each other as to make contact, but it is, of course, possible to inter- connect them also otherwise, by means of wire, a long clamp or the like. The connecting means may consist of a mechanical interconnecting element, such as a clamp, a rivet or the like, or a surface joint, such as a glue, a welding seam or the like. Other fixing elements are, however, also conceivable. The load exerted on the fixing elements is normally small since the fixing elements are only loaded if the mattress is unloaded, whereas there is no load at all if the mattress is loaded.

The mattress according to the invention can be manu- factured by the steps of enclosing springs in a casing material, biasing at least one of the springs and inter- connecting the springs. By the step of biasing the springs is, in this case, meant moving casing portions arranged for the ends of the spring towards each other and interconnect them by means of connecting elements in such manner that the springs in the biased state have a smaller longitudinal extent than in the original, non- biased state. This bias can occur either immediately after encapsulating the springs in the casing material, i. e. before assembling them to form a mattress, or when the mattress has been assembled. Preferably, the bias

occurs, however, when the springs are located in strings, and conveniently bias of all springs in the mattress layer occurs in this way.

A device for carrying out the method above comprises according to the invention an inserting means 11 and an abutment member 12 arranged at a distance therefrom. In use, springs are arranged so that one end is directed towards the inserting means and the other towards the abutment member. The inserting means is displaceable towards and away from the abutment member for moving cas- ing material at one spring end through the spring towards the casing material on the other side. Moreover, fixing means 13 are provided to form fixing members which inter- connect the casing materials from both spring ends. Pre- ferably, the inserting means is movable past the abutment member, and the fixing means is arranged on the opposite side thereof, as shown in the embodiment. In this manner, the inserting means can move the casing material out from both the front and the rear end of the spring through an opening in the abutment member while the abutment member prevents the spring from coming along. The fixing means can then fix together the casing materials with the aid of a mechanical fixing member, such as a clamp, or by means of surface joining, such as by gluing or welding.

A system according to the invention may advantageously comprise a plurality of parallel devices, such as two devices operating in parallel, which is shown in the embodiment. Fig. 3 is a top plan view of the device according to this embodiment of the invention, in a position where the inserting means 11 are not inserted towards the abutment member 12. Fig. 4a illustrates the same device, but seen from the side, with the inserting means 11 in a position where it is inserted past and through the abutment member 12. The casing material 2 is made to come along and can be fixed together with a clamp or the like by the fixing means 13. A finished spring

element according to the invention is also shown schema- tically in Fig. 4b.

It goes without saying that also other types of fix- ing means can be used. It is also possible to use a mov- able abutment member, in which case means on both sides of the spring are pressed towards each other, whereupon fastening, welding or equivalent interconnecting can take place. In this manner, the freedom of choice when placing the fixing element will, however, be affected.

Coil springs of many sizes can be used in connection with the present invention, and essentially any size of springs may be used. It is, however, preferable to use springs having a diameter of 2-10 cm, most preferred about 6 cm.

Moreover, it is preferred for the bias of the springs to be carried out so that the length of the springs in the biased state is smaller than 2/3 of the length of the same springs in the non-biased, original state, preferably smaller than 1/2. Moreover it is pre- ferred for the ratio of spring length to spring diameter in the biased state to be smaller than 2, preferably smaller than 1, most preferably smaller than 1/2.

As mentioned above, the casings with springs are arranged preferably in successive rows, after which such rows are fixed to each other side by side, as indicated in Fig. 2. Preferably, the rows are fixed to each other at 2-3 fixing points distributed in the vertical direc- tion in front of each spring. It goes without saying that a smaller or larger number of fixing points is possible.

It is also possible to arrange an extended fixing line essentially parallel with the longitudinal direction of the springs instead of a plurality of fixing points. The interconnection of rows can take place by welding or glu- ing. Also such interconnecting can, however, alternative- ly be effected by means of clamps, Velcro tape or in some other convenient manner.

With the inventive mattress, controlling of the spring is achieved, which is thus prevented from turning or the like. In this way, it is possible to make very thin mattresses, optionally down to a thickness of one or a few centimetres. The invention thus is well suited for seat cushions, bed mattresses to be placed on top of other mattresses and similar applications where thin mat- tresses are required. It is very advantageous to be able to make bed mattresses of coil springs in this manner, not only to be able to make them thinner, thereby increasing their comfort, but also since springs are normally not subject to fatigue as time goes by, as are polyethylene and like materials. Mattresses according to the invention can be made very light, soft and comfort- able, but also, owing to the bias, very stiff and hard, as desired.

By means of the invention, the height of the spring elements can easily be controlled by varying the position of the fixing member. The more the casing portions from the spring ends are moved towards each other and the more they are made to overlap when interconnected, the thinner and more compact the mattress. In this way it is also easy to provide different thickness in different portions of the mattress, or to provide mattresses having diffe- rent thicknesses, without having to change anything in the manufacturing process but the interconnection. The manufacture will thus be very flexible and controllable.

Particularly, it is possible to provide mattresses which are bowl-shaped or the like for use as seat cushions or other mattresses intended to be used as seats. Similar changes in height can also be used in other mattresses to control the user's position on the mattress.

By the casing material being pulled together over the springs according to the invention, the entire mat- tress is also pulled together to some extent. As a result, the mattress is stabilised, and no frame or the like is necessary. Furthermore, the pulling together may

force the springs to mesh somewhat while the casing mate- rial is arranged between them. This is desirable since this prevents the mattress from making noise that arises when uncovered spring turns strike against each other.

The invention has been described above by way of an embodiment. Several variants of the invention are, how- ever, conceivable. For instance, it is possible to use, as mentioned above, other types of fixing elements, as well as other casing materials, spring sizes etc. Fur- thermore the device and method can be designed in diffe- rent ways. Such close variants must be considered to be comprise by the invention as defined in the appended claims.