RU2309890C2 - Device to control electric drive of crane load-lifting/lowering mechanism - Google Patents

Abstract

FIELD: mechanical engineering; load-handling equipment.

SUBSTANCE: invention relates to electric drives of load-lifting/lowering mechanisms of load-lifting machines. Proposed device contains dc motor, thyristor rectifier, diode, shunting contactor, dynamic braking contactors and resistors. Thyristor rectifier is placed in electric motor supply circuit and is connected with generator. Diode is connected with thyristor rectifier. Lead of diode is connected to motor armature circuit. Shunting contactor shunts diode. Dynamic braking contactors with resistors placed in their circuits are connected with thyristor rectifier and dc motor.

EFFECT: improved reliability of operation of crane electric drive.

5 dwg

Description

This technical solution relates to electric drives for lifting and lowering the load of lifting machines operating according to the scheme "primary engine-generator-electric motor-lifting mechanism".

More specifically, a lifting mechanism is understood to mean a rope lifting and lowering mechanism used in the construction of hoisting cranes.

It is known from practice that when lowering the load with a crane operating according to the aforementioned scheme, the electric drive can operate in a generator mode with energy recovery to the network. In the absence of a network or other energy consumers, the main receiver of recuperated energy is a synchronous generator, which goes into motor mode. Part of the energy is dissipated in the form of losses in the synchronous generator, the rest of the energy is supplied to the shaft of the primary engine, while unloading it. Obviously, with an increase in the mass of the load being lowered and the lowering speed, the recovery power increases. It is known that a primary engine, such as a diesel engine, can take only about 30% of the power returned to its shaft from the rated power of the primary engine, and if the returned power is exceeded, unstable operation of the primary engine occurs. At the same time, the state of the primary engine and its power indicators, including the shaft rotation frequency and operation stability, have a significant impact on the stability of the operation of the associated electric drive of the lifting machine.

It is also essential for machines operating according to this scheme, for example, for cranes with recovery devices of potential energy received from moving down the load mass, that the received energy of movement through the mechanical drive of the crane and the electric motor of this drive is transmitted to the generator, and through the shaft generator to the shaft of the primary engine, while the excess energy supplied to the shaft of the primary engine can “knock over” it or create conditions for its operation to “peddle”. This leads to damage to the machine drive.

Another known significant drawback in the operation of the electric drive according to the motor-generator-electric motor scheme is the overturning of the inverter of the thyristor converter with a through short circuit of the armature of the direct current electric motor of the electric drive, and this tipping occurs when the electric drive is braked by the load lifting mechanism when lowering the load when the transition occurs from the rated speed of lowering the load by a crane to a lower speed of lowering the load. This tipping effect occurs when the drive is powered by a limited power network, in particular from a primary engine (diesel) through a generator. Moreover, the inverter overturning does not depend on the mass of the cargo and on the direction of its movement (up and down), but occurs at the moment when the converter goes into inverter mode.

It is also a problem for the overshoot of the prime mover’s rotational speed during an overrun and subsequent load shedding of the electric drive. This overshoot is especially evident when cranes are powered by mobile power plants that have high-speed protection based on microprocessor controllers. Moreover, operating personnel, as a rule, do not have the ability (or do not have sufficient qualifications) to change the protection settings.

The next problem is a sharp decrease in the speed of the prime mover until it stops when the electric drive starts in the direction of rise, when a load close to the rated load capacity of the crane is suspended on the hook of the hoisting crane. This drawback indicates the insufficient power of the mobile power station, from which the power is supplied to the crane, or the incorrect setting of the speed controller of the drive motor.

From the patent documentation, a vertical crane load drive is known comprising a load lifting mechanism motor connected via a switching unit to a power source, an additional direct current motor kinematically connected to a mechanical energy accumulator and electrically to a power supply, a load lifting mechanism electric motor brake release unit and decoupling diodes, and the drive is equipped with a voltage relay, the winding of which is connected to a power source, sources, one of which is connected in series with the excitation winding of the additional electric motor, which is connected through a single disconnecting contact of the voltage relay in parallel to its armature winding connected to the power source through one decoupling diode, the braking unit of the load lifting drive electric motor and its excitation winding through the other decoupling diodes are connected respectively to the armature winding of the auxiliary motor directly and through tionary included other break contacts voltage relays and another resistor - to the motor lifting mechanism [1].

In this device, during normal operation of the drive, the battery accumulates mechanical energy, and in the event of a power failure of one electric motor, it gives off energy, and one of the electric motors goes into generator mode and feeds the brake windings and the second electric motor, which allows you to smoothly lower the load, since the second electric motor starts work in dynamic braking mode.

A device for controlling an electric drive according to a generator-engine scheme of a crane lifting mechanism comprising a load sensor, an actuator, a setter, a control system, limit switches and a rheostat in the generator excitation circuit, the control device is made with an accuracy corrector of a pointer with a load weight limiter [2] .

Known reversible thyristor two-set DC electric drive designed for hoisting mechanisms, containing a mixed excitation motor, a series winding of which is connected in series with the armature through the rectifier bridge, and parallel to the armature of the motor and directly connected to it, operating in the descent mode, the rectifier bridge diode connected in series and braking resistor [3].

A device is known for controlling the movement of mechanisms of machines with drives, for example, according to a generator-engine scheme with a generator exciter, containing a task element, a controlled parameter magnitude sensor and a comparison body, and it uses photo-pulse value sensors as a task element and a controlled parameter magnitude sensor and the direction of movement of the master and controlled shafts, connected through a pulse synchronizer to the comparison body, made in the form of a binary reversal a pulse meter with converters of direct and reverse codes of the number recorded in the counter to voltage proportional to them, and two counter-wound windings of the exciter generator are connected to the outputs of these converters [4].

The solved and achieved task of this technical solution is to increase the reliability of the electric drive of a hoisting crane by eliminating or significantly reducing the influence of the value of the recovered power supplied to the supply network both in the static mode of operation of the electric drive and in transient modes of operation of the electric drive.

The stated technical problem is solved by the electric drive control device for lifting and lowering the load of the crane, which contains a DC motor, a generator connected to it, a thyristor rectifier installed in the electric motor supply circuit, a diode connected to it by a shunt contactor, resistors connected to the thyristor converter and dynamic braking contactors, one of which is connected to a resistor, while the diode is connected to the armature of the electric motor and thyristor a rectifier, a bypass contactor connected to the anode and cathode of the diode, a dynamic braking circuit coupled to the contactor armature of the motor, the other resistor is connected to the other terminal of the motor armature thyristor converter connected to the generator.

Figure 1 shows a schematic diagram of a control device for an electric drive mechanism for lifting and lowering the load of a crane.

Figure 2 - circuit speed reference thyristor rectifier electric drive mechanism for lifting and lowering the load.

Figure 3 - relay-contactor control circuit of the electric drive mechanism for raising and lowering the load.

Figure 4 - control circuit of the electric drive.

Figure 5 - arrangement of the control device of the crane.

The device (Fig. 1) contains a shunt contactor 1 included in the power circuit and and dynamic braking contactors 2 and 3, which are connected to a direct current electric motor 4. The motor armature circuit is connected to the output of the diode 5 and the dynamic braking contactor 3, while the anode and cathode diode 5 are included in the power circuit in such a way that prevents current flowing through it in the energy recovery mode when braking from a high ascent to a low ascent rate. Resistors 6 and 7 are introduced into the circuit of contactors 2 and 3.

The control device has a load mass limiter 8 connected to its power circuit (Fig. 4), a relay 9 of which is included in the logic input circuit 10 of the programmable controller 11.

The device (figure 3) contains contacts 12 and 13 of the starters. The relay 9 is installed in the circuit 14. The device (Fig. 4) contains a relay 15, an output relay 16 and a thyristor rectifier 17 (Fig. 1), operating in the rectifier mode and delivering electricity from the power supply circuit 18 of the crane to the electric motor 4. The electric drive contains a command controller 19 (FIG. 2), contact 20 (FIG. 4) of the programmable controller 11 and contact 21 of the output relay 16, as well as other elements that are in electrical connection with other elements shown in FIGS. 1-5, but which are not indicated digital positions.

An electric motor 4 (Fig. 5) is introduced into the electric drive by an electrical connection with a generator 22 and a mechanical connection with a lifting mechanism. An electric motor 4 is electrically connected to the generator 22 through a thyristor converter 17. Fig. 5 schematically shows a drive control device 23, which includes all of the above elements and the connections between them, except the generator 22. The control device 23 with the generator 22 is connected via an thyristor converter 17 to an electric communication 24, while the control device 23 is connected to the diode 5 and the contactor 2.

Generator 22 is mounted on shaft 25 of primary combustion engine 26. The lifting mechanism is a cargo winch with a drum 27, on which a load 29 is suspended by a rope 28.

The device operates as follows.

When lifting the load, the shunt contactor 1 and the contactors 2 and 3 of the dynamic braking are open. The diode 5 included in the armature circuit of the electric motor 4 prevents the flow of current in the energy recovery mode when switching from a high speed of a cargo to a low speed of its movement.

In the direction of lowering the load, the diode 5 is shunted by closing the contactor 1. In this case, there can be two options for the operation of the device.

The first option is if the load is heavy, then the contactor 2 is turned on and the resistor 6 is turned on. In the case of the engine 4 operating in inverter (generator) mode, the potential energy from the movement of the load 29 down (Fig. 5) is converted into electrical energy by the electric motor 4. Since the latter is electrically connected with the generator 22 through the electric drive control device 23, then when the electric energy is supplied by the electric motor to the electric power supply circuit, the excess electric energy is converted into thermal energy by the resistor 6. This eliminates inverter mode, when the energy from the electric motor 4 is given to the power supply circuit of the crane.

If the load is light, then the resistor 6 is briefly connected to the engine 4 when switching from a high speed lowering the load to a low speed of lowering it, and the braking energy is extinguished by the resistor 6 by converting electrical energy into thermal energy. In this case, the connection of the resistor 6 occurs when the command controller 19 (FIG. 4) is switched from the switch-on position “5” to the switch-on position “4” of the load descent.

The mass of the load on the crane hook is determined by the load mass limiter 8 (Fig. 4), the relay 9 of which is activated with a load of 0.5 of the nominal mass of the load to be lifted with contact 20 turned off, and with the contact 20 on, relay 9 of the load mass limiter 8 is triggered with the load 0.25 of the nominal mass of the lifted load. Thus, when the drive control device is excluded:

- excess return power and therefore unstable operation of the drive motor and the electric drive as a whole;

- "tipping" of the drive motor and creating the conditions for its operation "peddling";

- overturning of the inverter of the thyristor converter;

- overshoot of the rotational speed of the drive motor under conditions of overrun and subsequent load shedding during the operation of mobile power plants having high-speed protection based on microprocessor controllers;

- reduction of the rotational speed of the drive motor when the load is separated from the cargo area when a load close to the rated load capacity of the crane is suspended on the hook of the hoisting crane.

Information sources

1.SU 1299948 A1, 03/30/1987.

2. SU 528254, 09.15.1976.

3. SU 336756, 04.21.1972.

4. SU 218392, 05.17.1968.

Claims (1)

A control device for an electric drive mechanism for lifting and lowering a load of a crane containing a DC motor electrically connected to a generator, a thyristor rectifier installed in a power supply circuit of an electric motor and connected to a generator, a diode connected to a thyristor rectifier, the diode output being connected to an electric motor armature circuit, a shunt contactor that shunts the diode, dynamic braking contactors, in the circuit of which are introduced resistors connected to a thyristor a rectifier, while the contactors of dynamic braking are connected to a DC motor.

Images