The subject of the invention is a chair on a coil spring with a movement limiter, wherein the seat is fastened to the support via coil spring that allows a controlled swinging of the seat. Such chair has orthopaedic properties, as it imitates sitting on a ball, which is extremely favourable to the backbone and back muscles.

A chair on a coil spring is known from patents SI 20455 and 20508. A seat 4 is fastened to a platform 5 on the upper end of a coil spring 1 which is fastened at its bottom end via support 2 to a base 3 or to an adequate known lifting/sinking mechanism. The seat 4 is thus vertically movable in dependence of weight of the sitting person and it can especially swing

approximately circularly in all directions, with a pivoting point being approximately halfway of the spring height.

A problem which is not satisfactorily solved in the disclosed known chair is that the seat can swing too much and cause instability or even slipping or fall of the sitting person. The swinging of the seat is only limited by spring hardness.

The task and goal of the invention is to prevent too heavy swinging of the seat of a chair on a coil spring.

The task of the invention is solved by an independent claim.

The invention will be described by way of an embodiment and the enclosed drawings, showing:

Figure 1 : known chair on a coil spring,

Figure 2: detail of a known chair on a coil spring in projection,

Figure 3: detail of a known chair on a coil spring in cross-section,

Figure 4: detail with a movement limiter of the chair on a coil spring of the invention in cross- section, when the seat and the platform are not laterally burdened,

Figure 5: detail with a movement limiter of the chair on a coil spring of the invention in cross- section, when the seat and the platform are laterally burdened. Figure 4 shows a detail with a movement limiter of a chair on a coil spring of the invention in cross-section, when the seat and the platform 5 are not laterally loaded and are horizontal, i. e. parallel to the floor, on which the chair is located.

A support 2 is a link to the base, i. e. chair's legs and can simultaneously also be a mechanism for regulating the height of the seat 4 of the chair in order to adapt the height of the seat 4 of the chair to the sitting person. A coil spring 1 is fastened to the support 2 with its bottom end. At the upper end of the spring 1 a metallic, preferably steel bushing 8 is inserted into its interior. The external diameter of the bushing 8 is somewhat, i. e. from 0.1 to 0.5 mm, smaller than the internal diameter of the spring. The bushing 8 is circularly bent outwards for a right angle in the upper part in order to abut the end of the spring 1 and partially encloses it and simultaneously fully abuts the platform 5. The platform 5 is fastened to the spring 1 and the bushing 8. The seat 4 of the chair is fastened to the platform 5.

In the geometrical centre of the spring 1 a bar 6 is fastened on the top of the support 2. The bar 6 is a stiff metallic rod, which can be either rigid or slightly resilient. The length of the bar is smaller than the distance between the top of the support 2 and the bottom of the platform 5, when the spring 1 is unstressed. A length of the bar shorter than the distance between the top of the support 2 and the bottom of the platform 5, when the spring 1 is unstressed, is needed in order for the platform 5 not to touch the top of the bar 6 when the spring is stressed. The load is the weight of the sitting person. Hardness and resilience of the spring 1 are

dimensioned in compliance with declared top chair load, i. e. the weight of the sitting person. So this shorter length of the bar 6 is defined by the stress of the spring 1 at maximum allowed vertical load of the seat 4. The spring 1 bends to a side when laterally stressed i. e. when a person sits on the seat 4. This is shown in Figure 5. When the bend of the spring 1 is big enough and in order to prevent the tilt of the seat 4 from getting too big and thus the chair unstable, the bushing 8 touches the top of the bar 6 and a further tilt of the seat is herewith prevented. The internal diameter of the spring 1 and consequently the bushing 8 and the height of the bar 6 limit the swinging of the seat 4.

As an alternative variant remaining within the scope of the invention a bearing 7 can be arranged on the top of the bar 6. This is preferably a ball bearing with such internal diameter that it can tightly fit the top of the bar 6. The external diameter of the bearing 7 is adapted to the allowable tilt of the seat. The bearing 7 in this embodiment can roll in the interior of the bushing 8. Inconvenient friction of the top of the bar 6 against the bushing 8 is thus prevented. The internal diameter of the spring 1 and that of the bushing 8 as well as the external diameter of the bearing 7 and the height of the bar 6 limit the swinging of the seat 4. Alternatively and still within the scope of the invention the interior of the spring 1 and the bushing 8 can be coated with a 5-10 mm thick coat 9 of elastic material, preferably silicone rubber. This provides for a pleasant, soft and soundless fit of the top of the bar 1 or the bearing 7, when they lie against the coat 9 and not the bushing 8.