GB2055207A - Device for signalling load excess - Google Patents

Abstract

A device for signalling a load, such as a lift passenger load, exceeding a predetermined value comprises a sensor 10 attached to a load carrying member on which the load is exerted. The sensor comprises a plate member secured to the load carrying member and at least one strain gauge 21 mounted on the plate member. Signalling circuitry is responsive to a first signal received from the strain gauge. The circuitry includes a comparator 50 for comparing said first signal with a second signal representative of said predetermined load value to produce an overload signal when said first signal exceeds said second signal for a predetermined period. In one embodiment suitable for use with a lift car having a compensated rope arrangement, a compensating sensor produces a compensating signal in order that the effect of the rope may be eliminated. <IMAGE>

Description

SPECIFICATION Device for signalling load excess This invention relates to a device for signalling a load exceeding a predetermined value, and a lift incorporating such a device.

Such a device will find application in relation to the passenger loads of passenger or goods lifts, crane or lifting beam loads and the charging and discharging of conveying vessels with predetermined loads of one or more materials.

According to the present invention there is provided a device for signalling a load exceeding a predetermined value, comprising a sensor to be fixedly attached to a load carrying member on which the effect of the load will be exerted, said sensor comprising a plate member adapted to be secured to the load carrying member and at least one strain gauge mounted on the plate member, and signalling circuitry electrically coupled to the strain gauge and electrically responsive to a first signal received from the strain gauge thereto, said signalling circuitry including comparator means capable of comparing said first signal received from the strain gauge with a second signal representative of said predetermined load value and producing an overload signal when said first signal exceeds said second signal for a predetermined period.In the preferred embodiment, the comparator means incorporates setting means for varying said predetermined value of the load.

In a preferred embodiment, the sensor includes a bridge arrangement of four strain gauges two of which are not affected by the load applied to the plate member and act to compensate for ambient temperature variations. In this embodiment, the circuitry includes amplifier means with a variable zero setting to enable adjustment of said first signal for the no load condition. In this embodiment a common power source provides the operating voltage for the sensor and the comparator means so as to eliminate the effect of power source variations.

In the preferred embodiment, the overload signal is electrically connected to relay means for producing a visual and/or audible indication of the overload condition. The overload signal may also be employed to de-activate the load carrying member or apparatus with which it is associated e.g. lift or crane until such time as the overload is removed and the overload signal cancels.

With a lift, the use of such a device enables an audible and/or visual indication to be generated when the number of passengers exceeds the lift rating. The time delay prevents the comparator means hunting for an overload condition in the event of transistory variations such as a passenger stepping in and out of the lift. The comparator means may have a hysteressis characteristic to prevent on/off operation of the overload signal due to a person bouncing in the lift. The setting means of the comparator enables the device to be calibrated according to the passenger carrying load of the lift.When the device is intended for use with apparatus where a plurality of predetermined loads are to be signalled such as conveyor vessels to be filled or emptied successively with different quantities of material, then the comparator means may include separate stages each producing an associated overload signal for its respective predetermined load value.

In a further embodiment the device is intended for use with a lift car having a compensated rope arrangement, and the device further comprises a compensating sensor to be fixedly attached to a lower load carrying member on which the effect of the rope will be exerted, said compensating sensor comprising a second plate member adapted to be secured to said lower load carrying member and at least one strain gauge mounted on said second plate member, said compensating sensor being connected to said circuitry to generate a compensating signal representative of the effect of the rope on the lower load carrying member, said comparator means taking the difference of said first signal and said compensating signal for comparison with said second signal.

Preferably, compensating sensor includes a bridge arrangement of four strain gauges two of which are unaffected by the load applied to the second plate member and act to compensate for ambient temperature variations.

In this embodiment, the circuitry includes second amplifying means with a variable zero setting to enable adjustment of said compensating signal and a compensation setting to vary the gain control to enable adjustment of the compensating signal whereby the compensating signal may be adjusted such that the difference between the first signal and the compensating signal only varies in response to the load within the lift car. The invention also extends to a lift car incorporating the above defined devices for signalling a load exceeding a predetermined value.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a sensor of a preferred embodiment fixedly attached to a load carrying member of a lift; Figure 2 shows schematically the circuitry of one preferred embodiment of the device; Figure 3 shows a second embodiment in which a compensating sensor is also attached to a lower beam of a lift car; Figure 4 shows schematically circuitry for the embodiment of Figure 3 in which the additional circuitry associated with the compensating sensor has been added to the circuitry of Figure 2, and, Figure 5 shows an alternative form of sensor.

A first embodiment of the device for signalling a load exceeding a predetermined value is shown in Figures 1 and 2 where the sensor 10 is indicated in Figure 1 and the circuitry 26 is indicated in Figure 2.

The sensor 10 which has a casing 11 and plate member 12 is bolted to a load carrying member, namely beam 13 in Figure 1. This beam 13 is one of a pair of lift beams 13, 14 between which is mounted the pulley 1 5 for the lift cable 1 6 and which beams 13, 14 are arranged transversely of lift member 1 7. Desirably the plate member 12 is bolted at a location on the beam 1 3 mid-way between the pulley 1 5 and lift member 17.

The sensor 10 has the bridge of strain gauges 21 (Figure 2) arranged on the plate member 12 and protected by the sensor casing 11. The strain gauges 21 are arranged such that two of the gauges are active to respond to tension along the length of the plate member 13 and two of the gauges are "dummy" gauges for compensation of the bridge according to variations in ambient temperature. The lead 18 is for connection to a unit (not shown) which houses the circuitry of Figure 2 and includes the first signal line 22 and the bridge power supply line 23.

Turning to Figure 2 there is shown diagrammatically the circuitry of the device.

Sensor 10 is included for a description of the electrical operation although, as stated above, the sensor 10 is located on the beam 13 and connected to the unit which includes the signalling circuitry of Figure 2. In Figure 2, the sensor 10 receives its operating power along a power supply line 23 from power-source 30 which is a regulated power supply. The strain signal from the bridge of strain gauges 21 appears as a first signal along first signal line 22 to the amplifier means 40. This amplifier means 40 has a zero setting potentiometer 41 incorporated therein to enable. the zero load condition to be set in the absence of a pay load on the beam 13. The power line 25 for amplifier 40 is connected to power source 30.The output signal of amplifier 40, which is the amplified first signal, appears on input line 24 to the comparator means 50 which is also connected to power source 30 by power line 26.

Comparator means 50 is capable of comparing the first signal on line 24 with a second signal representative of a predetermined load value. The second signal is generated by the comparator means 50 from the power signal on the line 26.

The first and second signals are compared and when the first signal has the higher value an overload signal is generated on line 27. The trip point setting means 51 comprises a potentiometer which enables the second signal to be adjusted to represent the desired predetermined value, for example, a passenger load between 1 and 50 people. The comparator means 50 also incorporates means for delaying an output signal on the line 27 for a delay interval after the arrival of the first signal being compared: in practise the first signal will be present continuously when the device is in use and the delay time will be relative to an incremental change in the value of the first signal.Such a time delay delays the appearance of an overload signal (if generated) on the line 27 for an interval, such as half of a second, to prevent rapid hunting of the comparator means when a hesitant passenger enters and leaves the lift. The comparator means 50 also includes a hysteresis factor in its design to prevent on/off appearances of an overload signal on the line 27 due to a person bouncing in the lift. Suitably the hysteresis allows the predetermined value of the load to be set to a load tolerance equivalent to 0.4 of the estimated load per person. Line 27 leads to relay 60 which is also connected by power line 29 to power source 30.The relay 60 may have a pair of normally closed contacts contacted to a green lamp indicating that the load is within the operating range and a pair of normally open contacts contacted to a red lamp and/or an audible alarm to indicate, when the relay trips, that an overload condition exists. The normally closed contacts may be connected to the lift circuitry to cause the lift to cease operation when these contacts open due to the existence of an overload condition and the presence of an overload signal on line 27.

When the device is required to indicate a series of "overload" conditions, for example in connection with the incremental filling or emptying of a conveyor or vessel, then the comparator means may comprise a plurality of stages each associated with a separate line 27 and relay 60.

In the embodiment of Figures 1 and 2, the signalling device is incorporated in a lift where the cable 1 6 travels round pulley 1 5 and returns to the lift motor (not shown). The arrangement is such that the weight of the rope 1 6 does not influence the load on the beams 13, 14.

In Figure 3 the lift arrangement, and more particularly the arrangement of the rope 116 is different. The arrangement of the lift rope in Figure 3 is known as a compensated rope arrangement. Rope 11 6 passes from upper beam 13 to the lift drive and control, then depends below the lift car and is attached to lower beam 113. In consequence, the length of rope 11 6 below the lift car influences the load on the lift beams. In the lift arrangement of Figure 3 a main sensor 10 and a compensating sensor 110 are employed. As in Figure 1, the sensor 10 is employed to respond to tension in the beam 13.

The sensor 110 is employed to compensate for the effect of the rope 11 6 depending from the lower beam 113.

The control circuitry associated with the sensors 10 and 110 is shown in Figure 4 which is a modification of the circuitry of Figure 2. In the circuitry of Figures 2 and 4, like references designate like components. Thus in Figure 4 the additional circuitry is related to the additional sensor 11 0. In order to compensate for the rope 11 6, a compensating signal generated by the sensor 110 is employed at the comparator 50 to adjust the input on the line 24 - the compensating signal on line 124 is subtracted from the value of the signal on line 24.

The compensating signal is produced by the additional circuitry of power source 130, sensor 110 and amplifier 1 40 - these being counterparts of components 30, 10 and 40.

Sensor 110 and amplifier 140 are connected to power source 130 by lines 123, 125. Line 122 connects SENSOR 110 to amplifier 140. Line 124 connects amplifier 140 to comparator 50.

Amplifier 140 has zero setting means 141 and compensation setting means 142, which is a gain control.

In this embodiment, the lift car of Figure 3 is taken to its lowermost position. With the lift car in its lowermost position, and with power source 130 switched off, the adjustment of amplifier 40 and comparator 50 is made as described with reference to Figure 2. The power source 1 30 is then switched on and the zero setting 141 of the second amplifier 1 40 is adjusted to give a zero compensating signal. Then, the lift car is taken to its highest position (the top floor) and with no load in the lift car, compensating setting 142 of the amplifier 140 is adjusted to ensure that no 'Output signal' appears on line 27 to the relay 60.

Thereafter, the compensating signal on line 1 24 is proportional to the weight of cable 116 hanging below the lift car. The comparator 50 response to the difference of the first signal on line 24 and the compensating signal on line 124 such that the output signal on line 27 only varies in response to the load within the lift car.

The compensating sensor 110 comprises a second plate member 112 and is in other respects similar to the sensor 10 of Figure 1. Plate member 112 is secured to the beam 113. In particular, as shown in Figure 4, sensor 110 like sensor 10, comprises a bridge arrangement of four strain gauges 21.

In the aforegoing description of the embodiment of Figures 3 and 4 reference has been made to a compensated rope arrangement. It is intended that the expression 'compensated rope arrangement' should be construed to include arrangements which employ a chain for raising and lowering the lift cage. The rope or chain carries a counterbalance weight 1 50.

Referring to Figure 5, the embodiments of Figures 1 and 2 or Figures 3 and 4 may employ the sensor 210 (for the main sensor 10 or compensating sensor 110) shown diagrammatically therein. This sensor 210, known as a ring sensor, has four active strain gauges 221,231 arranged on a cylindrical body 220 which is bolted to a load carrying member, such as beam 113 of Figure 1, by bolts (not shown) passing through bolt holes 222. The sensor 220 is provided with a protective cap (not shown).

The strain gauges 221, 231 consist of a pair of gauges 221 arranged on the internal wall 224 of the body 220. Only one strain gauge 221 is seen in Figure 5 since the pair are diametrically opposite one another. These strain gauges 221 act as compression gauges. Another pair of strain gauges 231, which act as tension gauges, are arranged on the outer wall 226 of the cylindrical body 220. Again, only one is seen in Figure 5 as these gauges 231 are also diametrically opposite one another.

Electrically the gauges 221,231 are arranged in a bridge, like the gauges 21 in Figures 2 and 4, with gauges 221 on oppositely spaced limbs. It is advantageous to use ring sensors 220 on lifts, particularly older lifts, where the mechanical components are considerably heavier than those of modern lifts and where the output signal from a sensor such as sensor 10 of Figure 2 is low in consequence.

Claims (12)

1. A device for signalling a load exceeding a predetermined value, comprising a sensor to be fixedly attached to a load carrying member on which the effect of the load will be exerted, said sensor comprising a plate member adapted to be secured to the load carrying member and at least one strain gauge mounted on the plate member, and signalling circuitry electrically coupled to the strain gauge and electrically responsive to a first signal received from the strain gauge thereto, said signalling circuitry including comparator means capable of comparing said first signal received from the strain gauge with a second signal representative of said predetermined load value and producing an overload signal when said first signal exceeds said second signal for a predetermined period.

2. A device as claimed in Claim 1, wherein the comparator means includes setting means for varying said predetermined value of the load.

3. A device as claimed in either Claim 1 or Claim 2, wherein the sensor includes a bridge arrangement of four strain gauges two of which are not affected by the load applied to the plate member and act to compensate for ambient temperature variations.

4. A device as claimed in any one of Claims 1 to 3, wherein the circuitry includes amplifier means with a variable zero setting to enable adjustment of said first signal for the no load condition.

5. A device as claimed in Claim 4, comprising a common power source providing the operating voltage for the sensor and the comparator means so as to eliminate the effect of power source variations.

6. A device as claimed in any one of the preceding claims, wherein said device is intended for use with a lift car having a compensated rope arrangement, the device further comprising a compensating sensor to be fixedly attached to a tower load carrying member on which the effect of the rope will be exerted, said compensating sensor comprising a second plate member adapted to be secured to said lower load carrying member and at least one strain gauge mounted on said second plate member, said compensating sensor being connected to said circuitry to generate a compensating signal representative of the effect of the rope on the lower load carrying member, said comparator means taking the difference of said first signal and said compensating signal for comparison with said second signal.

7. A device as claimed in Claim 6, wherein said compensating sensor includes a bridge arrangement of four strain gauges two of which are unaffected by the load applied to the second plate member and act to compensate for ambient temperature variations.

8. A device as claimed in either Claim 6 or Claim 7, wherein said circuitry includes second amplifying means with a variable zero setting to enable adjustment of said compensating signal and a compensation setting to vary the gain control to enable adjustment of the compensating signal whereby the compensating signal may be adjusted such that the difference between the first signal and the compensating signal only varies in response to the load within the lift car.

9. A device for signalling a load exceeding a predetermined value, arranged, constructed and adapted to operate substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 1 and 2 as modified by Figure 5 of the accompanying drawings.

1 0. A lift car incorporating a device for signalling a load exceeding a predetermined value as claimed in any one of Claims 1 to 5 and 9.

11. A device for signalling a load exceeding a predetermined value, arranged, constructed and adapted to operate substantially as hereinbefore described with reference to Figures 3 and 4 or Figures 3 and 4 as modified by Figure 5 of the accompanying drawings.

12. A lift car with a compensated rope arrangement, incorporating a device for signalling a load exceeding a predetermined value as claimed in any one of Claims 6 to 8 and 11.