FR2630544A1 - Weighing device for measuring the load in lift cars - Google Patents

Abstract

Weighing device for measuring the load in lift cars. It consists of a chamber 6 filled with oil. The chamber is provided with a diaphragm 1 on which are situated strain gauges 2, 3, 4, 5. The weight to be measured is converted into pressure on the diaphragm by means of a bellows 7 which is an integral part of the chamber. This bellows 7 makes it possible to compensate for the differences in tension between cables. The chamber is pressed between a fixed plate and a plate for attaching the cables for pulling the lift. The four strain gauges 2, 3, 4, 5 are mounted in a Wheatstone bridge. The voltage imbalance, which is a function of the load, is amplified by an operational amplifier.

Description

 The invention relates to a weighing device for measuring the load in elevator cars.

 The purpose of this weighing is either to prevent the departure of the elevator in the event of an overload, or to prevent the interception of the cabin on one floor in response to a landing call on this floor if the cabin is full, in order to avoid an unnecessary stop.

 In another case, the weighing is used to cause the departure without delay of a cabin belonging to an elevator battery if this cabin is charged to a predetermined percentage.

 Known systems consist, for example, of incorporating one or more load cells with mechanical operation between the floor of the cabin and its stirrup. This is rarely possible for existing installations when this device has not been planned. In addition, there are self-supporting cabins without stirrups.

 In other embodiments, strain gauges are used on the upper or lower part of the cabin stirrup; but taking into account the safety coefficients used for dimensioning, according to the rules of the art, the deformations for a person are very small and, therefore, the precision and the fidelity are not satisfactory in the usual cases.

 The present invention relates to a load cell with strain gauges sensitive to the pressure of a fluid and the electronic system associated with it.

 This invention allows precise and faithful weighing by a device which is characterized by a simple assembly, adaptable on new or existing installations.

The invention is described in the following text with reference to the accompanying drawings, in which
Figure 1 shows, at scale 10, the arrangement of strain gauges on a membrane.

 Figure 2 shows in section the enclosure intended to transform the weight to be measured into pressure and forming a load cell.

 Figure 3 shows the mounting of the load cell on the cab suspension.

 Figure 4 shows the block diagram of the electronic system associated with the load cell.

 The load cell comprises a circular membrane (1) on which four strain gauges are fixed by known yen, generally by gluing.

 The gauges are of the heavy-duty type. They are arranged radially for two of them (2,4) and in an arc for the other two (3, 5).

 They are electrically connected to form a Wheatstone bridge.

The deformation of the membrane (1) is obtained by the fact that it forms part of the partition of an enclosure (6) of cylindrical shape filled with oil and that said enclosure carries at its upper part a bellows (7) which allows the weight to be measured to be transformed into pressure on the walls. The characteristics of the oil used are not critical. The bellows also has a primary advantage explained in the following text.

 The Wheatstone bridge gauges are supplied with power and the imbalance is measured by a four-pin connector of a known type.

 The weighing chamber (6) is placed between the usual suspension plate of the cabin stirrup (9) or suspension of the self-supporting cabin and an additional plate (10) further comprising a hole for fixing the balance by a screws (11).

 The two suspension plates may not be parallel due to uneven elongation of the traction cables (12). The measurement is not disturbed thanks to the bellows (7) which allows compensation for a parallelism defect of up to 10b, which is far beyond the usual tolerances. The weight, in all cases, is transformed into pressure and then into an electrical signal whatever the method of cable attachment and the number of cables. The minimum number of cables is two according to the rules of the art.

 The signal taken from the diagonal of the Wheatstone bridge (13) is sent to an operational amplifier (14) of a known type with an input voltage threshold adjustable by potentiometer (15). This calibration potentiometer eliminates the dead weight of the cabin and its accessories in order to measure a predetermined payload in the cabin.

 A delay circuit constituted by the resistor (16) and the capacitor (17) filters the unwanted signals. These are due in particular to vibrations generated by users entering the elevator car.

 The output signal of the operational amplifier is amplified by a power transistor (18) whose collector supplies a relay (i9). The contacts (20) of this relay are used for operating the elevator according to the purpose of the corm weighing explained above.

 The transistor (18) is protected against overvoltages by a diode (21).

The operational amplifier and the power transistor are supplied by a stabilized voltage source (V1) independent of the stabilized voltage source supplying the Wheatstone bridge (V2).

Claims (2)

Resell i cat ions 1 / Weighing device to measure the load in elevator cabs  new or existing, characterized by a bellows enclosure (6) (7),  forming a load cell by the action of oil pressure on a membrane (1) comprising  both four strain gauges (2, 3, 4, 5); strain gauges  are connected in Wheatstone bridge (13) whose tension on the diago  The measurement value depends on the suspended weight. This scale is attached to the  by means of a normally existing fixed plate (9) and an additional plate  clip (10) for attaching the traction cables (12) transmitting the weight  to measure. The bellows (7) of the scale, in addition to its trans function  pressure mission, is a means of compensating for the difference in  tension between cables. 2 / Device according to claim 1, characterized by the use of a  operational amplifier which amplifies the voltage delivered on the diago  Wheatstone bridge measurement nale (13). The amplifier input  includes means for filtering out unwanted signals (16, 17). The  output signals consist of the contacts (20) of the relay (19).  relay (19).  Taring is carried out by a potentiometer (15) which sets the threshold