RU2566459C1 - Limiting device of lifting capacity of bridge crane - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device includes measuring unit (1), the signal from which is supplied to weight measuring unit (2), then, it is supplied to the input of key (3) and the first comparison unit (4). The signal is supplied from the first comparison unit (4) to the input of key (3), from the output of key (3) to the input of the second comparison unit (5), from the output of which it is supplied to inputs of control unit (6) of an asynchronous motor and indication unit (7), from the output of surge value setting unit (8) to the input of the second comparison unit (5), from the output of maximum weight setting unit (9) of the load being lifted to the input of the first comparison unit (4).

EFFECT: detection of mechanism overload at the limit; prevention of accidents related to overload.

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Description

The invention relates to devices that ensure the safety of hoisting mechanisms, and can be used mainly on overhead cranes to prevent overloads of the lifting mechanism.

Known limiter lifting capacity of an overhead crane, having the ability to offset in the vertical plane of the support of the cargo drum mounted in the bearing, and a balancing device with which a lever is connected, interacting with a limit switch mounted in a housing with a cover and a cage with balls and an eccentric cup mounted on the aforementioned bearing and resting through the balls on the cage, while the lever is rigidly mounted on the eccentric cup. [A.S. No. 586093].

The specified device has the following disadvantages.

The response time of the protection is determined by the sum of the intrinsic response times of the mechanical part, the limit switch and the electrical circuit and is 0.8 ... 0.9 s. During this time, the load can be completely removed from the support, which in the future will lead to severe accidents, namely: disruption of coupling of the mechanism couplings, breakage of suspension devices, ropes and falling of the load.

The closest solution to the proposed device in technical essence and the achieved result is a device that ensures the safe operation of lifting mechanisms, which is a power supply unit, an analog-to-digital converter, a strain gauge, a microprocessor, an asynchronous motor control unit, including a relay control unit and a power contactor. [Operation manual OGSh-1.2. Signal control unit, digital-to-analog converter. (OGSh-1.2V with a DNA sensor)]. When you turn on the protective device, a series of checks are performed. The position of the hook override limit switch and the load are monitored using a strain gauge; after the emergency operation mode is recognized, the power supply to the lift mechanism drive is turned off. The disadvantage of the control device is the low accuracy of the effort measurement due to the significant difference in the measurement results of the load cells, which according to the passport data of the load cells is ± 10%.

The result of the low accuracy of the work of the force measurement circuitry can be severe accidents, namely: failure of the hoist drive brake devices during overload, malfunctioning of the connecting couplings of the hoist mechanism, breakage of ropes and suspension devices, and load fall.

The objective of the present invention is to increase the accuracy of measuring efforts and, as a result, to limit the excess of the mass of the lifted load above the declared factory characteristics, which leads to the prevention of the occurrence of these accidents.

The solution to this problem is achieved in that the device for limiting the carrying capacity of an overhead crane, comprising an asynchronous motor control unit, including a relay control unit and a power contactor disconnecting an asynchronous motor, is characterized in that it further comprises a measuring unit made on the basis of current transformers connected with primary windings into the phase conductors of the supply cable of the stator winding of the electric motor, the output of which is connected to the input of the mass measuring unit, the first output of which о is connected to the first input of the key, and the second output goes to the first input of the first comparison unit, the unit for setting the maximum mass of the lifted load, the output of which is fed to the second input of the first comparison unit, the output of which goes to the second input of the key, the output of which goes to the first input of the second the comparison unit, the output of which is supplied to the display unit and the control unit of the induction motor, from the output of the unit for setting the magnitude of the jump is fed to the second input of the second comparison unit.

Due to the use of a measuring unit 1, a unit 2 for measuring mass, a key 3, a first comparing unit 4, a second comparing unit 5, an asynchronous motor control unit 6, an indication unit 7, a jump value setting unit 8, and a maximum load weight setting unit 9 in the circuit As a result, the electrical parameters of the asynchronous electric motor are controlled, the accuracy of force measurement is increased, and, as a result, the excess weight of the lifted load is limited.

In FIG. 1 is a schematic diagram of the claimed device for limiting the carrying capacity of an overhead crane; in FIG. 2 - temporary operation diagrams of the blocks included in the device.

The device for limiting the carrying capacity of an overhead crane (Fig. 1) contains a measuring unit 1, the signal from which is supplied to the mass measuring unit 2, then it is fed to the input of the key 3 and the first comparison unit 4. From the first comparison unit 4, the signal is supplied to the input of the key 3, from the output of the key 3 to the input of the second comparison unit 5, the output of which is fed to the inputs of the asynchronous motor control unit 6 and the indication unit 7. From the output of block 8 for setting the value of the jump to the input of the second comparison block 5, from the output of block 9 for setting the maximum mass of the lifted load to the input of the first comparison block 4.

The measuring unit 1 is made on the basis of current transformers in the amount of three pieces included by the primary windings in the phase conductors of the supply cable of the stator winding of the electric motor. The secondary windings of current transformers are connected to the mass measurement unit 2, implemented on a circuit that adapts the signal for the ADC logic circuits. The first comparison unit 4 includes two operational amplifiers, which serve to set the lower and upper current values using adjustable resistances. Then follows key 3, made on the basis of the logical element "AND". The second block 5 comparison includes two operational amplifiers, which are used to set the lower and upper current values using adjustable resistances. Next, a normal operation mode indication unit 7 is installed based on transistors and an LED serving as an indication of the “operation” mode. The asynchronous motor control unit 6, made using transistors that control the relay coil, by means of which the contactor is activated and the asynchronous motor is switched off. At the same time, the indication fixing the “accident” mode lights up. Block 8 sets the magnitude of the jump and block 9 sets the maximum mass of the lifted load is made on the basis of potentiometers regulating the adjustable value.

In FIG. 2 (a-d) are shown: a — angular velocity of rotation of the engine; b - stator current of an induction motor; in - the cycle of the device when exceeding the mass of the load during operation; g - the cycle of the device with a normal mass of the load during operation; d - key operation.

A device for limiting the carrying capacity of an overhead crane is as follows.

At the time of starting the mechanism by means of a relay circuit from the measuring unit 1, an information signal is supplied to the mass measuring unit 2, then it is fed to the input of the key 3 and the first comparison unit 4. From the first comparison unit 4, the signal is fed to the input of the key 3, then to the input of the second comparison unit 5, from the output of which to the inputs of the asynchronous motor control unit 6 and the indication unit 7, from the output of the unit for setting the jump value to the input of the second comparison unit 5, s the output of block 9 of setting the maximum mass of the lifted load to the input of the first block 4 of comparison.

In the first block 4 of comparison, the following logical function is implemented:

where x (τ) is the output signal of the first comparison unit 8, which has two levels Off. and slave .;

m _day. - the value of the current mass of the cargo;

m _max - the value of the permissible mass of the cargo.

If the difference values _{deyc m.} is greater than or equal to the signal m _max , the signal from the output of the first comparison unit 4 does not pass to key 3 and operation stops. Otherwise, the signal is not considered alarm and work continues.

In the second block 5 of comparison, the following logical function is implemented:

where y (τ) is the output of the second comparison unit 5;

m _tech. - the value of the current mass of the cargo;

m _ass - the value of the permissible mass of the cargo;

m _speed - the value of the permissible mass jump.

If the difference of values (m _tech. -M _ass. ) Will be more than m _sk.dop. , then the output of the second comparison unit 5 will receive a signal to the input of the control unit 6 of the induction motor. And in the case when the sum of the values (m _tech. -M _ass. ) Will be approximately equal to m _sc. , the signal is considered non-emergency.

Inclusion of the system in operation (conditionally taken for the time instant τ = 0) occurs according to the signal (Start), shown in FIG. 2c. This signal is supplied from the local control panel by an operator of an overhead crane.

In FIG. 2a shows a graph of the change in the angular speed of rotation of the engine. The entire work cycle consists of three sections:

1. The first section (x = 0 ÷ τ ₁ ) is the acceleration section, where the engine moves with acceleration up to the moment τ _{1 of the} set nominal speed.

2. The second section is a section of movement with uniform speed.

3. The third section is the braking section (after the “Stop” command).

In FIG. 2b shows a graph of changes in the current values of the current of an induction motor. Starting from the moment of starting (τ = 0), the engine accelerates to a steady speed, which lasts until time moment τ ₁ (3-5 s), after which the current stabilizes (as does the rotation speed).

The output voltage U of the measuring unit 1 is proportional to the motor current.

U = I _d * k _tt * k _dt

where _KT - current transformer ratio,

to _d.t. - coefficient of the current sensor circuit.

The graph of the output voltage U repeats the dynamics of the current values of the stator current I _d . The output of the measuring unit 1 is the information input of the device.

The appearance of an alarm is ensured by the successive actuation of four blocks when monitoring the mass of the load at the power-on section of the crane and six blocks when monitoring the mass of the load throughout the entire period of operation. The accuracy of measuring the forces in the drive is determined by the error of the measuring current transformers, which with an accuracy class of 1.0 is ± 1%.

Thus, the proposed device allows you to recognize the presence of overload of the lifting mechanism already at the limit of + 1%, which is much more accurate than the analogue (10%), and to prevent the development of accidents associated with overload.

Claims (1)

A device for limiting the carrying capacity of an overhead crane, comprising an asynchronous motor control unit including a relay control unit and a power contactor disconnecting an asynchronous motor, characterized in that it further comprises a measuring unit based on current transformers connected by primary windings to the phase conductors of the winding supply cable the stator of an electric motor, the output of which is connected to the input of the mass measuring unit, the first output of which is connected to the first input of the key, and the second output arrives at the first input of the first comparison unit, the unit for setting the maximum mass of the lifted load, the output of which is supplied to the second input of the first comparison unit, the output of which is supplied to the second input of the key, the output of which is supplied to the first input of the second comparison unit, the output of which is fed to the display unit and an asynchronous motor control unit, the output of the jump value setting unit is supplied to the second input of the second comparison unit.

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