DESCRIPTION

The present invention relates to technique of elevators. The invention relates in particular to a system for the detection of the load of the cabin of an elevator.

An elevator is normally equipped with a system able to detect and measure the load of the cabin, i.e. the presence of one or more persons in the same cabin. Said system is useful for the managing of auxiliary functions, for example actuation of the internal light of the cabin when a person boards, but first of all it is important to detect whether the maximum allowed load is exceeded, for safety reasons. For example a control may be provided to hinder the start of the elevator if the load exceeds the maximum value.

It is known to make use of a weighing system integrated in the floor of the cabin. Said system in general comprises a plurality of sensors (typically load cells), for example at least one sensor in the central part and another four sensors at the corners of the floor. A single sensor located in a point of the floor could in fact miss the detection of a person standing in a corner of the cabin. A shortcoming of this system is the poor precision and the relatively high cost. The cabin is rendered more complex and costly by the presence of these sensors.

Other known systems provide for the measurement of the deformation of plates directly connected to the load-bearing cables. Another technique provides for the measure of deflection of a load joint in a load-sensitive position, for example on an arch or on the cables fastening plate. These systems have a low cost but are fairly imprecise and can only be applied to elevators suspended on metal cables; moreover it has been noted that the measure is subject to a considerable hysteresis leading to low precision.

The invention relates in particular to elevators of the so called self-supporting type, suitable for serving a limited number of floors and therefore particularly attractive for small homes and/or renovations where it is generally not possible to obtain the room for installation of a conventional elevator.

A self-supporting elevator essentially comprises a cabin, a frame structure comprising two vertical guides, a drive comprising a motor and at least one suspension means, which is preferably represented by a belt rather than cables with circular section. A self-supporting elevator is preferably without a counterweight, so that the overall dimensions are quite small. The known load detection systems, which have been discussed above, are not suitable and/or are not satisfactory, particularly in this type of elevators.

The invention aims to devise a system for the measure of the weight transported by an elevator, which is simple and inexpensive to make, and which allows accurate measure.

The object is achieved with an elevator according to independent claim 1 . Some preferred embodiments of the invention are described in the annexed dependent claims. An aspect of the invention also consists of a method for the detection of the load of a cabin of an elevator, according to independent claim 9.

According to the invention the load is measured by means of a measure of deformation of an interface plate between the cabin and a carriage. The term plate is meant to refer, for the purpose of the present invention, to a generic support member that may have any form. The measure is made with a suitable device, realized with a technique in itself known. For example a strain gauge associated with said plate can be used.

Said plate is the interface between the cabin and a carriage which is part of the drive system. The plate in a preferred embodiment comprises at least one first portion which is firmly connected to the cabin, and a second portion which carries a pulley or an assembly of pulleys and therefore is substantially connected to the carriage. The measurement system comprises at least one device for the measure of a relative displacement between the first portion and the second portion of plate. This displacement gives an indirect measure of the load of the cabin.

The advantages of the invention are essentially the compactness, the simplicity and the reduced installation time, without the need to modify the cabin. More particularly the sensors in the floor of the cabin are no longer required. The cabin is made simpler and consequently the cost is reduced. This advantage is particularly appreciated in self-supporting elevators wherein the overall cost needs to be reduced. The measure is accurate and is not influenced for example by the position of the load inside the cabin.

The invention is now described in greater detail and with reference to the drawings, which show non-limiting preferred embodiments thereof, in which:

Fig. 1 shows schematically an elevator according to a preferred embodiment of the invention;

Fig. 2 shows a detail of the elevator of Fig. 1 ;

Fig. 3 illustrates the measurement of the load by means of the deformation of the fastening plate between cabin and carriage, in the elevator of Fig. 1 , according to one of the embodiments,

Fig. 4 shows a variant of embodiment of said plate, and

Fig. 5 shows a further variant of embodiment of said plate.

Referring to the drawings, an elevator comprises a cabin 1 equipped with guides 2 and suspended on a belt 3 which is wound on pulleys 4. The example shows an elevator without counterweight. More particularly (Fig. 2) the cabin 1 is driven by a carriage 5 comprising a fixed part integral with the cabin and a suspended part. The fixed part is formed substantially by a plate 6 which carries an assembly of pulleys 4. The suspended part is denoted by 7 and comprises another assembly of pulleys 4, and is connected to the fixed part with a system dampened by means of springs 8.

The load of the cabin 1 is detected and measured essentially through the measurement of a deformation of the plate 6 which represents mechanically the connection member between cabin 1 and carriage 5.

In the examples of the drawings the plate 6 is substantially two-dimensional and flat.

According to the embodiment of Fig. 3 said plate 6 essentially comprises a central portion (or core) 10 which carries the respective pulleys 4, and two wings 1 1 which are bolted to the rear wall of the cabin. As a result the two wings 1 1 are substantially integral with the cabin, while the part 10 is substantially integral with the carriage 5, i.e. with the assembly of the belt 3 and pulleys 4. The parts 10 and 1 1 of the plate 6 are connected by ribbings 12 which have a determined flexibility and more particularly allow a displacement between the core 10 and the wings 1 1 .

A first way of measuring the load of the cabin 1 is to take a measure of the gap distance denoted by 13. Fig. 3 (a) relates to the empty cabin while Fig. 3 (b) relates to the loaded cabin. The weight of the cabin 1 is transmitted as a force L on the wings 1 1 rigidly connected to the cabin. The structure of the plate 6 is deformed under load, with the effect that the gap distance 13 reduces from a value 13a at rest, to a value 13b under load. Knowing the variables of the system including rigidity of the plate 6 and weight of the empty cabin 1 , said distance 13 can be correlated to the overall weight of the cabin in working conditions and therefore to the load.

In the embodiment of Fig. 4 the plate 6 has an upper bridge portion 14 which is substantially integral with the wings 1 1. A strain gauge 20 measures the gap distance 13 between the upper portion 15 of the core 10 and the above mentioned bridge portion 14. It shall be noted that the core 10 of the plate is substantially integral with the suspended part (pulleys and belt) of the carriage 5, while the wings 1 1 and the bridge portion 14 are essentially integral with the fixed part, i.e. with the cabin.

In Fig. 5 a different embodiment of the plate 6 and position of the strain gauge 20 can be noted. Said strain gauge 20 measures the deflection of a crosspiece 16 of the plate 6. Said crosspiece 16 has two end portions integral with the wings 1 1 , while the central part of said crosspiece 16 is connected to the core 10, via a ribbing 17. Consequently the crosspiece 16 bends under load and the deflection is detected by the sensor 20. The elongation of the everted section of said crosspiece 16 is correlated to a relative displacement between the core 10 and the wings 1 1 and indirectly to the load of the cabin 1 .

The electrical signal of the device 20 is transmitted to the control system of the elevator to detect the load of the cabin and in particular to detect a possible overload.

The drive system comprises other assemblies of pulleys integral with the load- bearing frame (Fig. 1 ) and is not described in detail, being not essential for the purpose of the invention. It is to be noted that the suspension means may comprise a single belt 3 or several belts. The assemblies of pulleys 4 preferably comprise coplanar pulleys and each assembly comprises a series of pulleys of decreasing diameter, as shown in Fig. 2.