The present invention relates to an electrical brake for lift and elevator car doors.

Lifts and elevators are provided with floor doors and car doors. The present invention relates to an electrical brake for car doors, which locks the wings of the car door in the opened position and in the closed position.

It is a requirement of lifts and elevators that the wings of the car door be locked under certain conditions (opening and closing) to prevent, for instance, the wings from suddenly closing during the entry or exit of the users or to prevent the wings from suddenly opening during the ascending or descending motion of the lift or elevator. This can occur especially in the case of lifts that travel at high speed and that are subjected to strong vibrations.

To lock the wings of the car door, the prior art provides for the use of a mechanical brake with jaw and related actuating lever.

However, such a system is not always effective.

DISCLOSURE OF INVENTION.

The aim of the present invention is to eliminate the aforesaid drawbacks and to make available a particularly simple and economical electrical brake that can be applied without substantial modifications even to existing lifts or elevators and that is extremely reliable and allows an effective locking of the wings of the car doors in the desired position.

Said aims are fully achieved by the electrical brake of the present invention, which is characterised by the content of the claims set out below and in

particular in that it is so shaped in such a way as to be interposed between an operating panel and a three-phase motor to keep the motor electrically locked in correspondence with the opened and closed position assumed by the wings of the doors.

BRIEF DESCRIPTION OF DRAWINGS.

This and other characteristics shall become more readily apparent from the description that follows of a preferred embodiment, illustrated purely by way of non limiting example in the accompanying drawing table in which the only figure illustrates the diagram of the electrical brake.

BEST MODE FOR CARRYING OUT THE INVENTION.

With reference to the figure, the reference number 1 globally indicates the electrical brake of the present invention, and in particular its circuit board, which is inserted in series between a known operating panel 2 (whereto no modification is required) and a three phase motor 3.

The electrical brake is powered directly from the mains and it can be positioned indifferently both on the car operator (i. e. near the motor) and on the operating panel of said car operator.

The braking action, which consists of locking the wings of the door in a certain position, i. e. the opened and the closed position, occurs by direct current keeping the motor powered.

The reference number 4 indicates the power supply of the brake board by means of an alternate current from the mains at 115 V or 230 V, single phase, which is transformed into low voltage at 48V by means of a transformer 5 with dual secondary, rectified to direct current by means of a rectifier bridge 6 of the diode type.

Moreover, from a single secondary winding is obtained the low voltage at 24 V, rectified to direct current by means of a simple rectifier circuit with single half-wave, useful to power the relays present in the logic part of the electrical brake circuit.

The reference number 8 indicates a relay tasked with switching the two contacts 8a (normally open) that inject the direct current on the motor.

The reference number 9 indicates a second relay that commands an auxiliary contact 9a (normally closed).

The reference number 10 indicates a third relay that drives contacts 1 Oa and 1 Ob (normally open) and the number 11 indicates a fourth relay that drives an auxiliary contact 11 a (normally closed) and a contact 1 lb (normally open).

The contacts 10a, lOb and lib section the three phase line for supplying power to the motor when the braking action is active, otherwise the are closed allowing the motor to run normally.

The reference number 7 indicates a sensor that detect the lack of voltage to supply power to the motor 3 coming from the operating panel 2 corresponding to the command to stop the motor (open door and closed door).

In this situation the sensor does not cause the switching of the two switches 7a (normally closed) and 7b (normally open), this condition triggers the opening of the auxiliary contact 9a and the closing of the contacts 8a so that the motor 3 is powered by a direct voltage able to keep the rotor of the motor 3 locked.

When the voltage returns from the operating panel 2 (travel to open and to close) the braking circuit (essentially constituted by the circuit part with the switches 7a, 7b and the relay 8 with the contacts 8a) is excluded allowing the

motor to run normally. In essence, the contact 7a is opened, the contact 7b is closed and the contact 9a normally returns to the closed position, allowing to enable the two relays 10 and 11; in this situation, the auxiliary contact 1 la is opened excluding the relays 8 and 9.

The reference number 12 indicates a switch tasked with excluding the relay 8 if it is desired to act manually on the doors of the system without having to remove the power supply to the electrical brake; in this case, the braking action is deactivated until a subsequent intervention on the switch to bring it back to the normal operating configuration.

The present electrical brake allows to effect an"electrical", and not just mechanical, braking of the three-phase asynchronous motors in correspondence with the closed door and open door positions, in opposition for instance to untimely movements caused by the return springs of the coupling blades between car doors and floor doors.

An advantage of the present brake is that it is applicable to all lifts and elevators without making any modifications to their operating panels and it can therefore be installed both in new lifts and in existing ones.

In essence in the present electrical brake the sensor 7 and the particular configuration of the relays 8, 9,10 and 11 have the function of switching from a resting position of the brake, in which the electrical brake is deactivated and the motor 3 is powered from the operating panel 2, to a position of activation of the electrical brake in which the motor, in the absence of voltage from the operating panel, is powered by a direct voltage of the electrical brake circuit, so that it remains locked in its own position.