JP2866637B1 - Control method and circuit such as lifting magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a circuit for controlling excitation and demagnetization of a large-capacity magnet portion of a lifting magnet mounted on a work vehicle such as a hydraulic shovel.

[0002]

2. Description of the Related Art When a lifting magnet is mounted on a work cart such as a hydraulic excavator, the efficiency of the work in transporting a reinforcing bar or the like is good. A DC current is supplied to the electromagnet used as the lifting magnet from a battery power source of the work cart or a dedicated power generator, and the electromagnet is excited / demagnetized by opening / closing a power switch. This electromagnet consists of a large-capacity coil and a large-capacity iron core in order to obtain strong attraction and attraction,
At the moment when the power switch is opened, a high voltage back electromotive force is generated by the self-induction action of the coil. This back electromotive force usually reaches about 5 to 6 times the supply voltage, causing sparks in the power switch unit, burning and wearing of the contacts, and adversely affecting the power supply system equipment.

The present inventor has already proposed Japanese Patent Application No. 9-22013 in order to demagnetize the residual magnetism of the electromagnet of the lifting magnet and the object to be attracted and shorten the time required for detaching the object to be attracted. In the circuit of FIG. 5 disclosed in this application, a forward / reverse connection circuit of a parallel connection and a cross connection each having a power switch contact with a main power supply circuit is provided as a changeover switch unit. Between the two poles of the main circuit between the changeover switch and the electromagnet, two short-circuit circuits for serially connecting a semiconductor energized in one direction and a normally open switch are connected in parallel in opposite directions.

This circuit keeps a switch of a separate short circuit closed at the time of forward connection or reverse connection, and returns the switch of this short circuit to open after a certain period of time after power-off. This action prevents sparks caused by excessive back electromotive force generated in the electromagnet when the power is turned off,
After the power is turned off, the electromagnet is reversely excited for a short time by operating the changeover switch unit to demagnetize the residual magnetism of the object to be attracted, and the object is released from the electromagnet.

[0005]

Problems to be Solved by the Invention Japanese Patent Application No. 9-22013
In the control method disclosed in the above publication, it is necessary to start the generator again, reversely connect the main electric circuit, and supply reverse power for a short time in order to release the adsorbed substance adsorbed by the residual magnetism. It takes some time to switch from to reverse connection. At this time,
If the power supply time in the reverse direction is too long, the object to be detached is attracted again by the reverse excitation, so that there is a problem that it is difficult to control the operation timing.

In addition, a large-capacity large-size switch is required as a changeover switch unit in two forward and reverse systems. For this reason, the power supply control panel becomes large, and the width of a bracket unit for accommodating the control panel becomes large. There is room for improvement in terms of weight increase due to the increase in size. In this control method, when the hydraulic operation valve is reversely operated by a momentary operation error, there is a risk that the electromagnet is instantaneously reversely excited and the object to be adsorbed falls.

The present invention has been proposed in order to eliminate inconvenience and malfunction in the above-described control method, and provides a control method for rationally and completely demagnetizing residual magnetism of an object to be attracted with respect to a lifting magnet or the like. It is intended to be. Another object of the present invention is to further shorten the disengagement time, and to keep the electromagnet in the attracted state for a while even when the operation pedal or the like is released, so that the transfer operation can be safely performed if the hydraulic operation valve is immediately returned to the original position. It is to provide a control method that can be continued. Another object of the present invention is to provide a simple, compact and inexpensive control circuit.
Still another object of the present invention is to provide a control circuit capable of avoiding accidental opening of a contact due to vibration or the like while preventing wear of a control device.

[0008]

In order to solve the above-mentioned problems, in the control method according to the present invention, for example, a power supply of a main electric circuit in a magnet unit such as a lifting magnet mounted on a hydraulic excavator, that is, a large electromagnet is cut off. Later, the current caused by the back electromotive force generated in the electromagnet is switched so as to flow from a normal short circuit through the resistance means.
As a result, this short-circuit current is rapidly attenuated, and the storage circuit is closed to store electricity in the capacitor. When the voltage between the terminals of the electromagnet drops to a predetermined value, a current flows from the capacitor to the electromagnet in the reverse direction, and the electromagnet is instantaneously reverse-excited.

When the control method according to the present invention is applied to a lifting magnet or the like, if the power of the main electric path in the magnet portion, that is, the large electromagnet is cut off, the current generated by the back electromotive force generated in the electromagnet is reduced to a normally closed switch. Flows from the negative pole side to the positive pole side. When the switch of the primary short circuit is opened by the signal of a separate switch, this short-circuit current is rapidly attenuated by flowing through the resistance means. Furthermore, when the switch of the power storage circuit closes with an instantaneous delay when the switch of the primary short circuit opens, and the voltage between the terminals of the electromagnet drops to substantially zero,
A current flows from the capacitor to the electromagnet in the reverse direction, and the electromagnet is instantaneously reverse-excited, thereby repelling the residual magnetism of the object to be attracted and separating the object from the electromagnet.

On the other hand, in the control circuit according to the present invention, a primary short circuit having a normally closed switch between the two main electric paths of the large electromagnet, a secondary short circuit having a desired resistance means, A switch that closes with a momentary delay when the switch of the short circuit is opened and a power storage circuit that connects a capacitor in series are connected in parallel. The primary and secondary short circuits are conducted in one direction from the negative pole to the positive pole, and a signal from a separate switch opens the switch of the primary short circuit, and immediately thereafter, the switch of the power storage circuit is opened. A closing operation closes the power storage circuit to store electricity in the capacitor. In this control circuit, the resistance means in the secondary short circuit has a configuration in which a plurality of voltage limiting circuit elements in which a plurality of semiconductors, resistors, or a combination of a constant voltage diode and a transistor are connected in series in the same direction are connected in series. Is one of

The control circuit of the present invention can be applied to a lifting magnet or the like, and the lifting magnet is
It has a magnet part installed below, a bracket part that is attached to the end of the arm of a work cart such as a hydraulic shovel, and a hydraulic motor drive generator that is housed between both bracket parts. Power is supplied to the main circuit of the DC power supply of the magnet part A blocking means is provided. In the lifting magnet (FIG. 8), a pressure switch is provided as a separate switch on the return side of the hydraulic circuit,
The pressure switch operates in conjunction with a reverse operation of the operation valve of the hydraulic motor for driving the generator, and a signal from the switch causes the back electromotive force of the magnet section to flow through the secondary short circuit having resistance means. To do. Instead of the pressure switch, a limit switch that operates in conjunction with the reverse operation of the hydraulically operated valve by a cam and a link may be provided.

In the lifting magnet (FIG. 8), the AC generator for driving the hydraulic motor is connected to the main electric circuit of the magnet unit via a rectifier, and the rectifier is connected to the positive electrode from the negative pole side of the main electric circuit of the magnet unit. A diode and a thyristor are arranged in series toward the side, and a power supply circuit of the AC generator is connected at an intermediate portion. On the other hand, the power supply cutoff means of the magnet unit comprises a firing voltage generator for applying a firing voltage to the gate of the thyristor and supplying a DC voltage when the output voltage of the generator is equal to or higher than a certain level, thereby generating power. Supply and cut off DC current in conjunction with start / stop of the machine.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The control method and circuit of the present invention are applied to quickly demagnetize a large-capacity electromagnet used for transportation or the like. The apparatus to which the present invention is applied is, for example, a lifting magnet which is used by being attached to the tip of an arm of a hydraulic shovel, and further includes a magnet part which is suspended from a cargo handling machine such as a crane. These magnet parts are attached to a work cart etc.
There are various forms regarding the presence / absence of the power supply unit and the structure of the mounting part. As an example, a generator-mounted lifting magnet as shown in FIG. 8 will be described.

The lifting magnet 1 includes a bracket 3 attached to a tip of an arm 6 of a hydraulic shovel. Inside the bracket part 3, a generator 12, a control panel 13, a power supply cable 14,
The hydraulic control valve block 15 and the like are installed. Hydraulic motor 1
1 is supplied with hydraulic oil via a control valve block 15 via a hydraulically operated valve 17 (FIG. 6) operated from a cab. On the other hand, the output power of the generator 12 supplies power to the magnet unit 5 via the control panel 13 and the power supply cable 14.

As shown in FIG. 1, the control panel 13 is provided with switch contacts Y 1, Y 1 of a power supply relay Y on main electric paths 40, 42 of the magnet section 5, and main electric paths 41, 4 in front of them.
3 is connected to the power supply cable 14, and the power cutoff means may be other mechanisms than the relay contacts Y1 and Y1. Electric circuit 4
Between 0 and 42, for example, a circuit 32 provided with a constant voltage relay VR and a circuit 33 in which a contact VR1 of the relay VR and a power supply relay Y are connected in series are connected in parallel. When the output of the generator 12 is equal to or greater than the set value, the relay VR operates to excite the power supply relay Y, close the switch contacts Y1 and Y1, and supply power to the magnet unit 5. When the output of the generator 12 is reduced by returning the hydraulic operating valve 17 (FIG. 6) to the neutral position, the relay VR
Opens the contact VR1, opens the contact Y1 of the power relay Y, and shuts off power to the magnet unit 5.

On the other hand, a semiconductor 4 is provided between the electric paths 41 and 43.
7 and a normally closed relay contact X in series, a primary short circuit 45, a series of semiconductors 48 as resistance means, a secondary short circuit 44 in series, and a closing operation of the contact X with an instantaneous delay when the contact X is opened. A power storage circuit 46 that connects the relay contact A and the capacitor C in series is connected in parallel. Short circuit 4
5 and 44 may conduct only from the negative pole side electric path 43 to the positive pole side electric path 41, and may share the semiconductor 47 as shown in FIG. Since the multiple semiconductors 48 are simply used as resistors, for example, the known resistor 4 shown in FIG.
9, or a configuration in which a plurality of voltage limiting circuit elements 50 combining a constant voltage diode and a transistor shown in FIG. 5 are connected in series.

The other control unit 31 incorporated in the control panel 13 includes, for example, a relay X0 (not shown) for opening the contact X in response to a signal from the external switch PS, and closing the contact A instantly after this operation. An active relay A0 (not shown) is incorporated. As a result, when the switch PS is operated, the relay contact X of the primary short circuit 45 is opened, and the contact A of the power storage circuit 46 is closed with an instant delay. The contacts X and A are switches provided in the circuits 45 and 46, and are not limited to relay contacts, and can be replaced with other switch means such as a transistor, for example.

As shown in FIG. 6, an external switch PS
Is a pressure switch 29 connected to the return line 23 between the operation valve 17 and the check valve 30 in the hydraulic circuit of the hydraulic motor 11 driven by the generator 12, for example. In this case, after the generator is stopped, the switch PS is turned ON in conjunction with the reverse operation of the operation valve 17. The switch PS is not limited to the illustrated pressure switch, but may be a limit switch or an independent operation switch that operates by operating the operation valve 17 in reverse.

When the generator 12 is an AC generator as shown in FIGS. 3 and 4, a diode 36 and a thyristor 35 that conduct from the minus pole side to the plus pole side of the magnet main circuit are connected in series, and The power supply from the AC generator is connected in the middle. At this time, the supply or cutoff of the DC power is controlled by the ignition voltage generator incorporated in the control unit 34 according to the output level of the generator 12.
Apply or cut off the ignition voltage to the gate of No. 5. In this configuration, since the power can be turned on and off without any contact, the reliability is improved because there is no deterioration or malfunction of the contact as compared with the method of turning on and off with the relay contact as shown in FIG.

The operation of the control circuit according to the present invention will be described.
The magnet unit 5 is brought close to the object to be adsorbed, and the generator 12 is started. When the generator 12 reaches the steady rotation speed, the power switch Y1 in FIG. 1 or the thyristor 3 in FIGS.
5, the DC power is supplied to the magnet unit 5, and the magnet unit adsorbs the object. When the operation valve 17 is switched to the neutral position after the object is conveyed, the generator 12 is rapidly decelerated, the output is reduced, the power relay VR is activated, the relay contact Y1 is opened, and the power is shut off. In the case of FIG. 3, the ignition voltage generator stops the voltage output to the gate of the thyristor 35 of the rectifier RCT and shuts off the power.

The current due to the back electromotive force generated in the magnet unit 5 when the power is cut off flows through the semiconductor 47 and the circuit 45 via the contact X of the primary short circuit 45. When this short-circuit current is left as it is, a solid line (t2
And between t3) and the dashed line on its extension,
At the same time, the magnetic force decreases in direct proportion, and when the magnetic force disappears, the adsorbed object falls.

When the pedal is depressed in the reverse direction at an arbitrary time t3 after the power is turned off, the switch PS is turned on and the contact X of the primary short circuit 45 opens, and the contact of the secondary short circuit 46 is momentarily delayed. A is closed. As a result, the short-circuit current flows through the circuit 44 via the multiple semiconductors 48, rapidly decreases due to the large resistance, attenuates as shown by the solid line between t3 and t4 in FIG. 2, and the magnetic force rapidly decreases. To zero.

Thereafter, as shown from time t4 to time t5 in FIG. 2, the electricity stored in the capacitor C of the power storage circuit 46 is discharged in the reverse direction, and the power supplied from the capacitor C causes the magnet unit 5 to reverse instantaneously. Excite. Due to this reverse excitation, the light adsorbed object that has been adsorbed without dropping due to the residual magnetism repels and falls immediately.

[0024]

Next, the present invention will be described based on examples, but the present invention is not limited to the examples. As shown in FIG. 8, a lifting magnet 1 to which the present invention is applied has a magnet section 5 attached below a horizontal base 2 and a pair of bracket sections 3 fixed above the base. The lifting magnet 1 is pivotally mounted on the arm 6 of the hydraulic shovel and the tip of the bucket link 7 by pins 4 and 4 in the bracket portion 3, and is rotatable in the front-rear direction by the expansion and contraction operation of the bucket cylinder 8. The angle and position of the magnet unit 5 of the lifting magnet 1 can be freely controlled by turning and running the hydraulic shovel and operating the arm 6, so that an object to be attracted such as scrap can be adsorbed and conveyed to the magnet unit 5.

A generator 12 driven by a hydraulic motor 11, a control panel 13, a control valve block 15 for the hydraulic motor, and the like are arranged in the bracket sections 3, 3. A power supply cable connects the control panel to the magnet section 5. Connect at 14, and attach hydraulic hose 10.10 'along arm 6. The hydraulic oil of the hydraulic motor 11 is supplied by a hydraulic pump 16 for driving a hydraulic shovel.
(See FIG. 6 or FIG. 7), via a hydraulic valve block (not shown), a hydraulic operating valve 17 operated from the operator cab, hydraulic piping 9, 9 ', hydraulic hoses 10, 10', and connections beside the bracket, Further, it is supplied via a control valve block 15.

The output of the generator 12 is controlled by the control panel 13
Is supplied from the power supply cable 14 to the magnet unit 5. The start and stop of the generator 12 are performed by operating a pedal (not shown) installed in the operator cab of the hydraulic shovel, and the magnet unit 5 is excited by the generator. Generator 12
Is a DC generator in FIG. 1 and an AC generator in FIGS. 3 and 4. In the case of the alternator 12 of FIGS. 3 and 4,
A rectifier R built in the control panel 13 'or 13 "
The DC power is converted by the CT, and the DC power is supplied to the magnet unit 5.

FIG. 7 shows the entire hydraulic circuit and electric circuit of the lifting magnet 1, and FIG. 1 shows details of the control panel 13 in the electric circuit. In FIG. 1, the output terminals of the DC generator 12 are connected to the plus-side electric circuits 40 and 41 and the minus-side electric circuits 42 and 43 of the control panel 13, and switch contacts Y1 and Y1 are provided between the two main electric circuits. . The generator 12 is connected to the magnet unit 5 via the switch contacts Y1, Y1 and the power supply cable 14.

A circuit 32 to which a constant voltage relay VR is connected, a contact VR1 of the constant voltage relay VR and a power supply relay Y are provided between the electric circuits 40 and 42 from the generator 12 to the contacts Y1 and Y1.
Are connected in parallel. Further, between the electric paths 41 and 43 from the contacts Y1 and Y1 to the magnet part 5, a semiconductor 47 conducting from the electric path 43 (minus pole) side to the electric path 41 (plus pole) side and a multiple semiconductor 48 in the same direction are provided. A secondary short circuit 44 connected in series, a primary short circuit 45 in which the semiconductor 47 is directly connected to the electric circuit 41 via a normally closed relay contact X, and a power storage circuit 46 in which a relay contact A and a capacitor C are connected in series. And are connected in parallel.

The multiple semiconductors 48, or diodes,
The potential difference acting as a resistor per unit is usually about 0.7 V
It is. About 80 diodes are connected, and 60 to 80
It is preferable to design so as to obtain a voltage drop of V.

In FIG. 5, in the secondary short circuit 44 ″, a plurality of known voltage limiting circuit elements 50 combining a constant voltage diode and a transistor are connected in series in place of the multiple diode 48 shown in FIG. The circuit element functions the same as the multiple diode 48 as a resistance means.
That is, the circuit element 50 has a characteristic of being in a conductive state when a certain potential difference acts, and when a voltage equal to or more than a predetermined value acts on a transistor of the circuit element, a constant state is connected between the collector terminal and the base terminal of the transistor. When the voltage diode conducts and a voltage is applied to the base terminal of the transistor, a current flows from the collector terminal to the emitter terminal of the transistor, and a predetermined potential difference is generated.
This effect occurs sequentially and sequentially in the voltage limiting circuit elements 50 in the series arrangement.

For example, in the circuit element 50, the constant voltage diode conducts at a voltage of about 5 V and is applied to the transistor to be in a conductive state. Therefore, the potential difference per circuit element is 5 V. About 12 circuit elements 50 are connected,
It is preferable to design so that a voltage drop of about 60 to 80 V can be obtained.

On the other hand, the control unit 31 in the control panel 13
Are connected to the branches from the electric circuits 40 and 42. Although not shown, the control unit 31 includes a primary short circuit 4
The relay X0 of the contact X of No. 5 and the relay A0 of the contact A of the power storage circuit 46 are incorporated. In the control unit 31, a signal line is led from the contact point PS of the pressure switch 29 (FIG. 6), the relay X0 is excited by the ON signal of the contact point PS, and the circuit is configured so that the relay A0 is excited with an instantaneous delay. In order to secure the voltage of the control unit 31 for a short time even if the current supply from the electric circuits 40 and 42 is stopped,
Are connected in parallel with the power supply of the control unit 31.

In the overall view of FIG. 7, the control valve block 15 of the hydraulic circuit is indicated by a dotted frame, and details thereof are exemplified in FIG. In FIG. 6, a flow control valve 25 is provided in the feed line 22,
And, a check valve 30 is provided in the return line 23. The hydraulic control valve 17, which is a three-position four-way valve operable from the operator cab, is connected to the hydraulic pump 16 by a pipe 19,
9 is provided with a relief valve 18 for setting the primary pressure on the primary side, the upper limit of the supply pressure is limited by this relief pressure, and the relief oil is returned to the tank 21.

The secondary relief valve 24 is installed in a pipeline 28 connecting the pipeline 22 between the operation valve 17 and the flow control valve 25 and the pipeline 23 between the hydraulic motor 11 and the check valve 30. The check valve 26 is connected to the pipeline 22 between the hydraulic motor 11 and the flow control valve 25 and the pipeline 2 between the connection point of the hydraulic motor 11 and the pipeline 28.
3 and the check valve 26 allows only the flow from the pipe 23 side to the pipe 22 side. The pressure switch 29 is connected to the return line 23 between the operation valve 17 and the check valve 30.

In FIG. 6, when the hydraulic operation valve 17 is operated in the forward direction (parallel position), the hydraulic oil discharged from the hydraulic pump 16 flows into the supply side pipeline 22, passes through the flow control valve 25, 11 and drives the hydraulic motor 11 to rotate. This hydraulic oil supplies a constant flow rate adjusted by the flow control valve 25 to the hydraulic motor 11, bypasses excess oil from the secondary relief valve 24 to the return line, and
The upper limit of the operating pressure of 1 is set by the secondary relief valve 24. On the other hand, the hydraulic oil discharged from the hydraulic motor 11 passes through the return pipe 23, returns to the operation valve 17 via the check valve 30, and returns to the tank 21 from the pipe 20.

When the hydraulic operation valve 17 is neutralized during the operation of the hydraulic motor 11, the hydraulic oil is supplied to the pipeline 2 having the check valve 26.
7, the hydraulic motor 11 is rotated by inertia because the return pipe 23 is bypassed from the return pipe 23 side to the feed pipe 22 side, and the generator 12 continues power generation for a while. At this time, when the hydraulic operation valve 17 is operated in the opposite direction (cross position in FIG. 6), the feed pipe 1
9 and the return line 23 communicate with each other, but the high-pressure oil is blocked by the check valve 30 and does not reverse the hydraulic motor 11. This high-pressure oil acts on the pressure switch 29, turns on the contact of the pressure switch 29, and inputs a switch signal to the electric control panel 13 because the pressure switch is the external switch PS (FIG. 1).

When the hydraulic operation valve 17 in FIG. 7 is operated in the forward direction (parallel position), the hydraulic motor 11 and the generator 12 are started. When the output of the generator 12 reaches a certain level or more, the constant voltage relay VR (FIG. 1) is excited to close the contact VR1 of the circuit 33 to excite the power supply relay Y. As a result, the switch contacts Y1 and Y1 of the main electric paths 40 and 42 are closed to supply power to the magnet unit 5, and the magnet unit sucks and adsorbs the object to be adsorbed. At this time, the magnet part 5
The exciting current flowing through the coil of FIG.
The current changes according to the current level curve corresponding to t2, and the magnet unit 5 holds the object to be attracted.

After the object to be sucked is transferred to the target position by the hydraulic excavator, the hydraulic operation valve 17 is returned to the neutral position. Generator 1
2 keeps rotating only by the inertial force, and when the output voltage falls below the set value of the constant voltage relay VR due to a decrease in the rotation speed,
The contact VR1 is opened, the relay Y is de-energized, and the power switch contacts Y1 and Y1 are opened to cut off the power supply to the magnet unit 5.

The cutoff generates a back electromotive force in the magnet unit 5, and the back electromotive force is transmitted between the semiconductor 47 and the primary short circuit 4.
5 flows from the side of the electric circuit 43 of the magnet unit 5 to the side of the electric circuit 41 through the normally closed relay contact X. At this time, since the resistance of the multiple diodes 48 of the secondary short circuit 44 is large, the short circuit current of the back electromotive force flows through the circuit 45 having a small resistance value without passing through the circuit 44. When the operation valve 17 remains in the neutral position, the short-circuit current flowing through the magnet unit 5 is gradually attenuated by the internal resistance of the coil of the magnet unit, and attenuates along a line shown by a broken line after time t2 in FIG. However, the magnetic force gradually decreases with the current decay.

At time t3 in FIG. 2, when the operation valve 17 is operated in the reverse direction by depressing the pedal in the opposite direction, the check valve 3
The pressure between 0 and the hydraulic operation valve 17 becomes high pressure, high-pressure oil acts on the pressure switch 29, and the contact PS (FIG. 1) of the pressure switch turns on. As a result, the relay X0 of the control unit 31 is excited to open the contact X of the circuit 45, so that the short-circuit current flows from the circuit 45 to the circuit 44. Since the circuit 44 has a higher resistance, this short-circuit current rapidly attenuates to zero as shown by the curve shown by the solid line from time t3 to t4 in FIG. 2, and the magnetic force of the magnet unit 5 disappears, thereby causing a heavy load. The adsorbed material falls under its own weight, but the light adsorbed material does not separate due to residual magnetism.

The control unit 31 excites the relay A0 with an instantaneous delay from the excitation of the relay X0,
The contact A of the power storage circuit 46 is closed with an instantaneous delay from the opening operation of the power storage circuit 46, so that the capacitor C of the power storage circuit 46 is charged so that the lower electrode plate in FIG. Therefore, when the short-circuit current becomes zero at time t4, the electric power stored in the capacitor C instantaneously flows in the reverse direction from the electric circuit 43 to the electric circuit 41 through the magnet unit 5. This reverse current is negligible depending on the capacitance of the capacitor C, and from time t4 to time t4 in FIG.
5 flows like a curve shown by a solid line, slightly excites the magnet portion 5 and repels the residual magnetism of the attracted object, so that the attracted object is instantaneously separated from the magnet portion 5.

Next, FIGS. 3 and 4 show an embodiment in which an AC generator 12 is used instead of the DC generator shown in FIG. In FIG. 3 or FIG. 4, the circuit configuration from the generator 12 to both output terminals of the rectifier RCT corresponds to the circuit configuration from the DC generator to the relay contact Y1 in FIG. 3
5 corresponds to the relay contact Y1 in FIG. Generally, when a firing voltage is applied to the gate, the thyristor rectifies the AC power and outputs it as a DC power, and when the firing voltage is cut off, there is no function of rectifying the AC power.
The thyristor 35 is also used as a rectifier and a contactless switch.

Control unit 3 in FIG. 3 or FIG.
4, the relays X0, X0 in the control unit 31 of FIG.
In addition to incorporating A0 and the battery BT and their control circuits, an ignition voltage generator (not shown) for applying an ignition voltage to the gate of the thyristor 35 of the rectifier RCT is added. In FIG. 4, the secondary short circuit 44 '
Instead of the multiple diode 48 used in FIGS. 1 and 3, a known resistor 49 is used.

In the lifting magnet having the electric circuit shown in FIG. 3 or FIG. 4, the magnet unit 5 is brought close to the object to be adsorbed by operating the hydraulic shovel, and the hydraulic operating valve 17 is switched to start the generator 12. When the generator 12 reaches the steady-state rotation speed, the thyristor 35 serving as a power cutoff unit operates to supply a DC current to the magnet unit 5, and the magnet unit 5 adsorbs the object to be adsorbed.

When the object is transferred to a predetermined position, the pedal is released to return the hydraulic operation valve 17 to the neutral position. When the supply of the hydraulic oil is cut off, the generator 12 is rapidly decelerated to reduce the output, and accordingly, the power is cut off. The current caused by the back electromotive force generated in the magnet unit 5 at that time flows from the semiconductor 47 via the contact X of the primary short circuit 45, and if left as it is, the short circuit current becomes a solid line and a broken line between t2 and t3 in FIG. And the magnetic force decreases in proportion to this.

When the pedal is depressed in the reverse direction at time t3 after the power is turned off, the switch PS is turned on and the primary short circuit 45
X contact is opened. This short-circuit current is generated by the multiple semiconductors 48.
Alternatively, it flows through the circuit 44 or 44 ′ via the resistor 49, rapidly attenuates due to the large resistance, and the magnetic force of the magnet unit 5 rapidly decreases to zero. Thereafter, the magnet part 5 is instantaneously reverse-excited by the discharging action of the capacitor C of the power storage circuit 46, thereby desorbing the light adsorbed object that remains adsorbed by the residual magnetism.

[0047]

According to the control method of the present invention, even if the pedal is accidentally released during operation of the lifting magnet or the like, the electromagnet is not immediately demagnetized, and if the pedal is immediately depressed again, the adsorbed object does not fall. So high safety. In this control method, unless the switch signal is forcibly transmitted by depressing the pedal in the reverse direction, the attracted state is maintained for a while by the magnetic force due to the back electromotive force generated in the electromagnet when the power is turned off, and the attracted object is immediately It does not fall.

In the control method of the present invention, when the object to be adsorbed is released from the electromagnet, the pedal may be released and then depressed in the opposite direction, and only the object to be adsorbed is released by the reverse exciting force generated slightly after degaussing. Yes, operation timing is simple and operation is easy. Applying the control method of the present invention eliminates the need for a driver's intuition and skill-based driving operation, and completely removes the object by simply operating the pedal in the reverse direction or sending another switch signal. Therefore, the work load on the driver can be reduced.

The control circuit of the present invention does not require a large control panel storage space, is compact, and achieves a reduction in the weight of the device and an improvement in operability. In the circuit of the present invention,
A DC conversion mechanism that uses a diode and a thyristor as the power cutoff mechanism eliminates sparks at the time of cutoff because the supply and cutoff of power are made non-contact compared to using a large power relay switch. In addition, it is possible to prevent a control device from being worn out and to avoid a random accident in which contacts are opened due to vibration or the like.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a control circuit according to the present invention.

FIG. 2 is a graph showing a current change during a demagnetizing operation of a magnet unit in the control circuit of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the control circuit of the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the control circuit of the present invention.

FIG. 5 is a circuit diagram showing a fourth embodiment of the control circuit of the present invention.

FIG. 6 is a hydraulic circuit diagram showing an example of a drive circuit of a generator used for a lifting magnet.

FIG. 7 is a schematic block diagram showing the entire hydraulic circuit and electric circuit of the lifting magnet.

FIG. 8 is a partial side view showing a state in which a lifting magnet is attached to an end of an arm of a hydraulic shovel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lifting magnet 3 Bracket part 5 Magnet part 11 Hydraulic motor 12 Generator 13 Control board 17 Hydraulic operation valve 29 Pressure switch 30 Check valve 40, 41, 42, 43 Main electric circuit 44 Secondary short circuit 45 Primary short circuit 46 Power storage Circuit 47, 48 Semiconductor 49 Resistor 50 Voltage limiting circuit element

Claims (6)

(57) [Claims] After a power supply of a main electric circuit in a large electromagnet is cut off, a current caused by a back electromotive force generated in the electromagnet is switched to flow from a normal short circuit through a resistance means, and this short current is rapidly changed. Attenuates and closes the storage circuit to store electricity in the capacitor, and when the voltage between the terminals of the electromagnet drops to a predetermined value, a current flows from the capacitor to the electromagnet in the reverse direction and instantaneously reverse excites the electromagnet. Law. 2. When a power supply of a main electric circuit in a large electromagnet is cut off, a current due to a back electromotive force generated in the electromagnet flows from a negative pole side to a positive pole side through a primary short circuit provided with a normally closed switch. When the switch of the primary short circuit is opened by a signal of a separate switch, the short-circuit current becomes 1
From the secondary short circuit, a secondary short circuit having resistance means flows from the negative pole side to the positive pole side, and is rapidly attenuated by flowing through the resistance means, and when the switch of the primary short circuit is opened, When the switch of the power storage circuit closes with a momentary delay, the power storage circuit is closed and the electricity is stored in the capacitor.When the voltage between the terminals of the electromagnet drops to substantially zero, current flows from the capacitor to the electromagnet in the opposite direction. A method of controlling a lifting magnet or the like that instantaneously reversely excites the electromagnet to repel the residual magnetism of the object to be attracted and separate the object from the electromagnet. 3. A primary short circuit provided with a normally closed switch, a secondary short circuit provided with desired resistance means, and an opening operation of the switch of the primary short circuit between both main electric paths of a large electromagnet. A power storage circuit that connects a switch and a capacitor that are closed in time with a momentary delay and a capacitor in series is connected in parallel, and the primary and secondary short circuits are conducted in one direction from the negative pole side to the positive pole side. A control circuit such as a lifting magnet for opening the switch of the primary short circuit by a signal from the switch and immediately closing the switch of the power storage circuit to close the power storage circuit and store electricity in the capacitor. 4. A lifting magnet comprising: a magnet section installed below; a bracket section pivotally attached to an end of an arm of a work cart such as a hydraulic shovel; and a hydraulic motor driven generator housed between both bracket sections. A primary short circuit in which a normally closed switch is provided between the two main power paths of the magnet unit, a secondary short circuit in which a desired resistance means is provided, A switch that closes with a momentary delay when the switch of the short circuit is opened and a power storage circuit that connects a capacitor in series are connected in parallel, and the primary and secondary short circuits are connected from the negative pole side to the positive pole side. Direction, and the switch of the primary short circuit is opened by a signal from a separate switch, and immediately thereafter, the switch of the storage circuit is closed to close the storage circuit, and the capacitor is closed. A control circuit for a lifting magnet which stores electricity in the magnet and when the voltage between the terminals of the electromagnet falls to substantially zero, instantaneously reversely excites the magnet portion to repel the residual magnetism of the object to be attracted and to separate the object to be attracted. 5. The resistance means in the secondary short circuit comprises a plurality of series-connected semiconductors, resistors, or a plurality of voltage limiting circuit elements in which a constant voltage diode and a transistor are connected in series in the same direction. 5. The control circuit according to claim 3, wherein the control circuit is one of the following. 6. In the lifting magnet, an AC generator for driving a hydraulic motor is connected to a main electric path of a magnet section via a rectifier, and the rectifier is connected from a negative pole side to a positive pole side of the main electric path of the magnet section. A diode and a thyristor are arranged in series, and a power supply circuit of the AC generator is connected at an intermediate portion thereof.On the other hand, the power supply cutoff means of the magnet section is provided when the output voltage of the generator is equal to or higher than a certain level. A firing voltage generator that applies a firing voltage to the gate of the thyristor and supplies a DC voltage;
5. The control circuit according to claim 3, wherein the supply and cutoff of the direct current are performed in conjunction with the start / stop of the generator.