-Electronic device for measuring weights in elevator cars.

DESCRIPTION The present invention relates to a weight measurement device in the elevator cars comprising new and improved weight sensors connected to an electronic exchange provided with peculiar electronic components and circuits adapted to compensate the variations due to mechanical defects or deformation of the elevator car as well as to agents such as temperature and relative humidity which could affect a mere mechanical system. At the present status of art most of apparatus for weight measurement in the elevator cars are based on mere mechanical principles and require frequent calibra¬ tions as they are depending upon the general mechanical conditions of the system as well as the variations of the environment such as temperature, humidity a.s.o. This means that the measurement have a degree of accuracy which is absolutely unacceptable .

The task of the present invention is to provide measurement wich are generally independent of mechanical and environmental factors.

This has been provided by:

- weight sensors provided with a ball assembly allowing the moving part of the footboard to be bent under the action of the applied weight without impairing the result of the measurement;

- an input circuit processing the algebraic

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sum of the stresses exerted on the sensors, thus allowing the output signal to be constant whatever the load distribution in the elevator car may be.

This allows the mechanical parts of the apparatus to be simplified as eventual faults of coupling between the moving part and some sensors are annulled by the fact that a load decreasing on some sensors is compensated by a load increasing of the same amount on the other sensors; - sampling the output signal of the input circuit by a sampling circuit and then integrating it by an integrating filter. This allows a good immunity to the eventual noise at the input of the amplifying chain to be achieved due to the short length of the sampling signals and the long period of the integrating filter as well;

- a self-calibration system, i.e. a dynamic zero setting system for the reference scale allowing slow input signal variations due to temperature, humidity, aging of components a.s.o. to be compensated, while assuring the constancy of the zero setting during the measurement. This is achieved by a dynamic balancing control circuit which only in case of a fast variable signal (i.e. when a person gets on the footboard of the elevator) sends a signal to the input of a plurality of threshold circuits which are suitably calibrated for different operating conditions of the elevator such as overload, complete load, half load and occupied. If the unbalancing condition in the dynamic balancing control circuit is sufficient to trigger the threshold circuit corresponding to the condition of "occupied", such an operation allows through a switching assembly a digital counter to be operated, to the output of which a

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digital-analog (D/A) converter generating a little by little increasing analog signal is connected. Such a signal is compared by means of a comparator with the input signal which after sampling is amplified and integrated in order to be affected only by very slow variations . When the analog signal overcomes such a threshold value the comparator emits a signal blocking the digital counter through said switching assembly. Thus, the digital storing of the analog signal preceding the fast variation of the input signal is achieved, i.e. the storing of the analog signal corresponding to a static condition relative to the temperature an the humidity at a given time. Therefore, until the weight is heavier than that necessary to operate the threshold circuit of "occupied", the reference signal for carrying out the measurement at one input of the dynamic balancing control circuit is fixed and proportional to the output signal of the D/A converter.

Therefore such a signal is a constant refer- ence signal in which respect any variation of pressure on the weight sensors applied under the footboard of the elevator car will be immediately detected.

On the contrary,when the sensors are relieved from the previously exerted pressure and then the threshold circuit of "occupied" is in the off-state such a condition of the threshold circuit will cause the switching assembly to supply to an input of the dynamic balancing control circuit the amplified and integrated signal relative to the present state. Thus the reference signal at said input of the dynamic balancing control circuit is oscillating and

adapted to follow eventual low variations due to temperature a.s.o. which then will be still not affecting the output signals.

Further features and advantages will be readily apparent from the following description whith reference to the accompanying drawing illustrating an exemplifying, not limitative, preferred embodiment.

In the drawing :

Fig. 1 is a block diagram of the electronic exchange;

Fig. 2 is a perspective view of a weight sensor according to the invention;

Fig. 3 shows schematically the assembly of sensors in an elevator car; Fig. 4 illustrates the waveforms of the output signals of the a.c. amplifier, the period divider, the sampling circuit and the integrating filter, respective¬ ly;

Fig. 5 is a detail of the measurement bridge of the input circuit.

BRIEF DESCRIPTION OF THE BLOCK DIAGRAM Referring to Fig. 1 the present measurement apparatus comprises following groups or blocks :

Block A, comprising the weight sensors 1, an input circuit 2, an a.c. amplifier 4 and a square wave generator 3.

In this block of the apparatus an a.c. signal proportional to the pressure exerted on the weight sensors 1 is provided. Block B, comprising the sampling circuit 5, the period divider 6, the integrating filter 7 and the d.c. amplifier 8.

The output signal of this block a d.c. signal proportional to the a.c. output signal of the block A.

Block C, comprising a digital counter 20, the output of which is connected to a digital -analog D/A converter 21. In this block the digital storing and the analogue conversion of the output signal of the block B is provided.

Block D, comprising the d.c. amplifier 14, the comparator 18, the flip-flop 19, a first electronic switch 15, a second electronic switch 16 and an invertor-amplifier 17.

The output of the d.c. amplified 14 is connected to the input of the electronic switch 15 and to the first input of the comparator 18. The output of the electronic switches 15 and

16 are connected to the input of the inverter-amplifier 17. The input of the electronic switch 16 and the second input of the comparator 18 are connected to the output of the D/A converter 21. The output of the comparator 18 is connected to the input of the flip-flop 19, the output of Ql of which is connected to the input of the electronic switch 16. The output Q of the flip-flop 19 is connected to the input of the digital counter 20 and to the electronic switch 15.

In this block D the switching between the output signals of the block B and C depending upon the state of the threshold circuit 12/D of the block G is provided. Block E, comprising a dynamic balancing control circuit 23, a d.c. amplifier 9 and an amplifica¬ tion control means 24.

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The output signal of the d.c. amplifier 8 and the output signal of the inverter-amplifier 17 are fed to the two inputs of the balancing control circuit 23, respectively. In this block E a d.c. signal proportional to the difference between the output signal of the block B and the output signal of the block D is provided.

Block F, comprising the detector 22 sensing the on-state of the safety circuits, the electronic switch 10, the storing capacitor 25 and the d.c. amplifier 11. The output of the detector 22 is fed to the input of the electronic switch 10 which is also connected to the output of the amplification control means 24.

At the output of this block F a signal is provided which is proportional to the output of the block E when the safety circuits are in the off-state, said signal being proportional to the content of the storing capacitor 25 when the safety circuits are in the on-state. Block G, comprising the threshold circuits

12A, 12B, 12C and 12D with the respective output relays 13A, 13B, 13C and 13D.

The output signals of this block G are proportional to the output signals of the block F. WEIGHT SENSOR

Referring to Fig. 2 the weight sensor accord¬ ing to the invention comprises a plate 24 which is made integral with the stationary part of the weighing system, said plate supporting through two steel balls 26 freely rotating within stationary spherical seats 26a a measure¬ ment cross bar 28 supporting in turn on its upper face two further steel balls 30 placed along the median line

of the plate and rotating within stationary seats 30a. The plate 32 integral with the moving part of the weighing system is supported by the latter balls 30a.

At least one strain gage 34 is attached to the measurement cross bar 28.

The use of the lower pair of balls 26 and the upper pair of balls 30 placed along axis x and y oriented at 90° to each other allows exact contact points between the balls and the measurement cross bar to be provided even if the plate 32 integral with the moving part is laying on a plans which is not perfectly parallel to the plane of the plate 24 integral with the stationary part of the system.

The operation of the sensor is in practice as follows:

The pressure exerted on the plate 32 attached to the moving part (footboard) of the elevator car is transferred through the balls 30 to the measurement cross bar 28 which as already mentioned is supported through the balls 26 by the plate 24 which is made integral with the stationary frame of the elevator car.

The measurement cross bar 28 bends under the action of said pressure so that the produced deflection is transformed into a stretching of the lower part and a shortening of the upper part of the bar. Both deforma¬ tions can be sensed by a strain gage 34.

Depending upon said deformations the strain gages 34 of the footboard very their resistive character¬ istics which are sensed and amplified by the input circuit 2 of Fig. 1.

DESCRIPTION OF THE INPUT CIRCUIT The input circuit 2 is illustrated in Fig.5.

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It consists of a bridge circuit connected to all sensors 1 (1A, IB, 1C and ID) which are each provided in the present embodiment with a strain gage 34A, 34B, 34C, 34D, respectively. The variations of the resistive characteri

-sties of said strain gages 34A, B, C and D are sensed and amplified by the bridge circuit in which the electrical unbalance state is detected by feeding an a.c. signal provided by the generator 3. To better explain what above, the square wawe generator is connected to two opposite nodes of the measurement bridge formed of the strain gages 34A, 34B, 34C, 34D, and the a.c amplifier is connected to the other two opposite nodes of the bridge. Since as it is known a variation of the same sign (for example, an increase of resistance) in opposite branches of the bridge (for exaple, 34A, 34D) makes the bridge out of balance so that the sum of the variations is detected, and a variation of opposite sign with respect to the first variation (for example, a decrease of resistance) in the other two branches (for example,

34C, 34B) makes the bridge out of balance and is summed to the first variation, the unbalance state at the input of the a.c. amplifier 4 is equal to the sum of the variations detected by the four strain gages.

The output signal of the amplifier 4 of Fig. 1 (exemplified by the wave form A of fig. 3) is then sampled with a predetermined recurrence frequency by the output of the period divider 6 of Fig. 1 (waveform B of Fig. 3) so that the output signal of the sampling circuit 5 is proportional to the amplitude of the signal of the amplifier 4 corresponding to the sampling signals (as

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seen from the waveform C of Fig.3). As the pulse time of the sampling signals is very short (10 msec) and the integration time of the integrating filter 7 is about 200 msec, the output signal of the integrating circuit (Fig. 4, waveform D) is particularly stable and not affected by outer noise which should interfere at the same time as the sampling signals B of Fig. 3 and have a pulse time longer than 200 msec, in order to cause the distortion of said output signal. Thus a threshold is provided to overcome all noises that are present on the electrical line of an elevator.

DESCRIPTION OF THE ELECTRONIC CIRCUIT The output signal of the integrating filter 7 is amplified by the d.c. amplifier 8 and then by the d.c. amplifier 14.

Under initial condition, i.e. after the present apparatus is installed and energized, the flip-flop 19 is set so that its output Q switches on the electronic switch 15 and its output Q switches off the electronic switch 16, thus allowing the output signal of the d.c. amplifier 14 to be fed to the input of the inverter-amplifier 17.

Since the gain of the chain formed of the integrating amplifier 14, the electronic switch 15 and the inverter-amplifier 17 is exactly -1, the input signal of the d.c. amplifier 9 can be set to zero by acting on the dynamic balancing control circuit 23 because the input of which connected to the d.c. amplifier 8 is fed with a signal of the same amplitude but of opposite sign. Therefore, even if slow variations of the output signal of the d.c. amplifier 8 should be caused by the influence of temperature, humidity, aging of the

components in the chain proceding said amplifier 8 (in which chain said variations would have a determinant influence as the signals are very low) , the output signal of the d.c. amplifier 9 is balanced and equal to zero. Should the variations of the input signal of the integrating amplifier 14 be faster than the integra¬ tion time constant of said amplifier (for example, when a person rises on the moving part (footboard) integral with the plate 32 (Fig. 2) and causes a deformation of the cross bar 28, thus generating a fast variable output signal at the output of the strain gages 34) the output signals of the dynamic balancing control circuit 23 would be not anymore the same and with opposite signs as before. Thus, the unbalance output of the dynamic balancing control circuit 23 will be amplified by the d.c. amplifier 9 and will reach the input of the threshold circuits 12 through the amplification control means 24, the electronic switch 10 and the d.c. amplifier 11.

Said thereshold circuits 12 are calibrated with threshold values increasing from 12D and 12A and cause the respective output relays 13A/D to be triggered.

The threshold of the circuit 12A corresponds to the load condition of "overload", while the threshold of the circuit 12B relates to the condition of "com¬ plete", that of circuit 12C to the condition of "half load" and that of the circuit 12D to the condition of "occupied" . If the unbalanced output signal of the dynamic balancing control circuit 23 is sufficient to trigger the threshold circuit 12D, a signal is fed to the flip-flop

19 so that its outputs Q and Q change their states, thus causing the switching off of the electronic switch 15, the switching on of the electronic switch 16 and the operation of the digital counter 20, to the output of which the digital-analog D/A converter 21 is connected.

A little by little increasing binary digit is then provided at the input of the digital counter 20 so that a little by little increasing analog signal is generated at the output of the D/A converter 21. When such analog signal fed to the input of the comparator 18 overcomes the signal fed to the other input of the same comparator 18 from the output of the integrating amplified 14, the comparator will generate an output signal which through the flip-flop 19 will stop the counter 20, thus fixing the output signal of the converter 21.

In this way the digital storing of the signal preceding the variation depending on an effective use of the elevator is provided. Said signal, after being fed in an analogue way through the electronic switch 16 and the inverter-amplifier 17 to one input of the dynamic balancing control circuit 23, generates the reference signal with respect to which any variation of pressure on the sensors 1 is immediately sensed, thus providing the measurement of the weight lying on the sensor.

As long as the weight is heavier than that necessary to trigger the threshold circuit 12D, the reference output signal of the dynamic balancing control circuit 23 with respect to which the measurement are effected remains fixed and proportional to the output of the D/A converter 21.

On the contrary, when the sensors 1 are

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relievied of the previously exerted pressure and then the threshold circuit 12D is switched off, the flip-flop 19 is caused to change the state of its outputs Q and Q so that the electronic switch 16 is switched off and the electronic switch 15 is switched on. This will establish a connection between the output of the integrating amplifier 14 and the dynamic balancing control circuit 23 through the electronic switch 15 and the inverter-ampli¬ fier 17. Thus, as already mentioned, the reference output signal of the dynamic balancing control circuit 23 is oscillating and adapted to follow slow variations due to temperature a.s.o. , which will still be not affecting the output circuits . In order to avoid false measurements due both to accelerations and decelerations of the elevator car and to the movement of the people within the car itself, there is provided a detector 22 sensing the on-state of the safety circuits, i.e. the condition in which the door of the elevator car is closed. Under these circumstances the detector 22 switches off the output circuits by disconnecting through the electronic switch 10 the output of the amplification control means 24 from the input of the d.c. amplifier 11 connected to the storing capacitor 25:

A preferred embodiment of the invention is herein described and illustrated. It is self evident that many modification and changes may be made by the skilled in the art without parting from the scope of the present invention and the aim that the invention seeks to provide.