The present invention relates to a method for varying the mass of a counterweight and to a counterweight with a variable mass, for use in particular in the sector of lifts and elevators.

Within the sector of lifts it is necessary to ensure, for safety reasons. that the doors on the various floors should remain closed when the lift is not present at a floor. Also during the periodic maintenance operations, when the operator with a suitable tool or a special spanner intentionally unlocks a door on a particular floor in order to open it, said door must automatically close again by means of a safety device ensuring automatic closing.

Said device may consist of one or more recall springs or of a counterweight.

One of the main drawbacks of the springs consists in the variation of the recall force which, over time, may decrease with a consequent loss in the necessary safety conditions during closing.

Counterweights, on the other hand, have the drawback of requiring a somewhat wide range of different weights depending on the size and mass of the doors which they must cause to close. Therefore, counterweights formed by a plurality of parts of predefined weight are present on the market, said parts being able to be engaged in succession on a base support and being in the form, for example, of a plurality of cylindrical elements mounted on a shaft.

However, the individual parts have a predefined weight and do not allow fine adjustments of the closing force exerted by the counterweight and moreover it is necessary to keep a large number of parts of different sizes in store, thereby occupying a considerable amount

of space.

DISCLOSURE OF INVENTION.

The object of the present invention is that of eliminating the abovementioned drawbacks and allowing a substantially continuous and fine variation of the mass of the counterweight in an extremely simple and low-cost manner, without the need for keeping a plurality of individual sample weights in store.

Said objects are fully achieved by the method and by the counterweight which form the subject of the present invention and are characterized by the contents of the claims indicated below.

In particular, the method envisages that a counterweight having the form of a container provided with at least one inlet and/or outlet opening may vary its overall mass by means of the introduction (or removal) of a ballast consisting of material in granular, powder or liquid form which is added (or removed) via the opening in the container.

The counterweight comprises a container provided with at least one opening through which a ballast material in granular, powder or liquid form, preferably consisting of lead powder, is introduced.

BRIEF DESCRIPTION OF DRAWINGS.

These and other characteristic features will emerge more clearly from the following description of a preferred embodiment illustrated, purely by way of a non-limiting example of embodiment, in the accompanying plate of drawings, in which the sole figure shows a partially sectioned view of the variable-mass counterweight according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION.

With reference to the Figure, I denotes in its entirety a counterweight used specifically, but not exclusively, for lifts and elevators and constructed in the form of a cylindrical

tubular body 2, which is internally hollow so as to form a container which is folded and closed at the top and houses internally a cylinder 3, preferably made of lead or in any case material with a high specific density.

The cylinder 3, which forms a ballast element, is a solid cylinder with dimensions such that it can be introduced in a close-fitting manner inside the tubular body 2 where, moreover, additional cylinders of the same type may also be present, said cylinders if necessary having dimensions and a mass different from those of the cylinder 3, but in <BR> <BR> <BR> <BR> <BR> accordance with a variation of embodiment not shown it is also possible for the cylinder 3 not to be present.

The closed top part of the tubular body 2 is provided with holes 4 for attaching the counterweight to cables not shown.

The tubular body 2 is provided with an opening 5 on its side surface through which a ballast material 9 may be introduced into the tubular body 2.

A first annular element 6 made of plastic material is slidable externally in a close-fitting manner on the tubular body 2 so as to pass from a closed position of the opening 5 to a position in which the opening 5 is left free.

A second annular element 7, which is entirely similar to the preceding one, is fixed on the outside of the cylindrical body 2. Together, the pair of annular elements 6 and 7 form a noise-suppression means, so as to dampen the noise of the counterweight during vertical sliding thereof.

The ballast material 9 preferably consists of lead powder, but may also consist of another material in granular, powder or also liquid form, namely a material in a form such as to allow filling (or emptying) of the tubular body in a continuous and gradual manner, with the possibility of a high degree of precision in determining the final overall mass of the counterweight. _

For example, if the counterweight consisting solely of the tubular body 2 with the cylinder 3 inserted is defined as an"unballasted counterweight", and if three different unballasted counterweights having a mass of about 3 kg, about 5 kg and about 7 kg are available, and if the dimensions of the unballasted counterweight are such as to allow insertion of about 2 kg of lead powder, with the three unballasted counterweights of the type indicated above it is possible to achieve a variation in a substantially continuous manner from a total minimum mass of about 3 kg to a total maximum mass of about 9 kg.

The Figure shows a tubular body 2 provided with a single opening 5, but according to a variation of embodiment not shown it is possible to envisage the presence of additional openings. In particular it is possible to envisage a bottom opening for discharging the ballast material, but in this case the cylinder 3 is formed with dimensions such as to allow the passing or the discharging of the ballast material between the external surface of the cylinder 3 and the internal surface of the tubular body 2.

In the case, however, where the cylinder 3 is inserted inside the tubular body 2 in a substantially close-fitting manner, the bottom end of the tubular body 2 may be closed or may be open, with an opening having a diameter less than that of the cylinder 3 (for example with the presence of a folded edge 8 of the tubular body 2) so as to prevent the cylinder itself from coming out. In any case, the fact that the cylinder 3 is inserted inside the tubular body 2 in a substantially close-fitting manner, also prevents the lead powder from escaping.

In order to vary the mass of the counterweight, the method according to the invention envisages, in an original manner, the gradual and continuous addition of ballast performed so as to allow minimum variations in the total mass of the counterweight and therefore extremely fine and precise adjustment of the mass of the latter, which is not possible, for example, with the addition or the removal of a plurality of further cylinders entirely

similar to the cylinder 3 and with different dimensions and masses.

It is therefore not necessary to have a plurality of ballast cylinders of various dimensions to be introduced into the tubular body in order to vary the overall mass of the counterweight, since it is sufficient to have an adequate supply of lead powder or other material suitable for achieving a fine variation (with tolerances of about 1 gramme or even less) of the mass of the counterweight.

This fine adjustment is particularly useful when, over the course of time, the mechanical characteristics of the door to be closed vary for reasons of age or wear, thus requiring a corresponding adaptation of the recall force exerted by the counterweight.