JPH05343222A - Contactless control circuit for lifting magnet - Google Patents

Abstract

PURPOSE:To improve the operability of a lifting magnet by compensating the excitation characteristics automatically at the time of attraction and release. CONSTITUTION:The contactless control circuit has a DC power source having a smoothing capacitor C1 connected in parallel to a rectified power source Rec, and a bridge control circuit BCC composed of power transistors Tr1, Tr2, Tr3, and Tr4 connected in parallel to bridge-connected diodes D1, D2, D3, and D4 respectively, connected in parallel to the DC power source. Besides, it has a lifting magnet LM connected to the midpoint of the control circuit through a current detector CT, a drive circuit DCC which receives a signal from the current detector CT, is operated by a control switch, and sends a signal to each base B1, B2, B3, or B4 of each power transistor, a main control circuit MCC having the control switch Sw which controls the drive circuit DCC, and a pulse width modulation circuit PWM.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact control circuit for a lifting magnet used for cargo handling work for adsorbing scrap such as iron scrap and transferring it, and particularly when using the lifting magnet, when adsorbing scrap. The present invention relates to a circuit configuration for automatically controlling contactlessly controlling a magnetic characteristic that changes minutely when released.

[0002]

2. Description of the Related Art Generally, magnetic control circuits for lifting magnets of this type can be roughly classified into a contact control circuit system using a relay and a contactless control circuit system using a thyristor. In addition to the fact that the control equipment itself becomes larger and heavier due to the use of, the contactless control circuit method has become a momentum in that it not only causes contact damage and noise generation but also shortens the life of the controller itself. . Although it is a non-contact control, a thyristor is in widespread use as an element to be used.

[0003]

However, since a thyristor is a self-holding type element, once the gate signal is input and ignited, the main current must be reduced below the holding current value. Since it cannot be cut off, a separate arc extinguishing circuit must be provided, and a reverse current for cutting off the main current must be supplied from this circuit, and the charge stored in the capacitor is used as its energy source, which can be instantaneously used. Although the arc of the thyristor is extinguished by discharging, if the thyristor is used in the control circuit of the lifting magnet, the following inconvenience occurs. That is, a: In the lifting magnet control circuit,
A positive excitation circuit for attracting a magnetic substance and a reverse excitation circuit for surely releasing the magnetic body are provided, and the positive excitation circuit cannot be surely cut off when shifting from positive excitation to reverse excitation for release. If the reverse excitation circuit operates, the power supply voltage will be doubled and the power supply circuit will become a kind of short-circuit state, causing an overcurrent and an accident. In such an accident, a release signal is sent at a time when the arc-extinguishing capacitor is not sufficiently charged, so sufficient energy to extinguish the thyristor on the positive excitation side cannot be obtained. It occurs when the release signal is input immediately after the signal is input. B: In the conventional type, since the switching of the high voltage supply to the rated voltage is dependent on the time setting by a timer or the like due to the suction material such as scrap, there is an inconvenience that the time setting must be changed depending on the suction material. is there. C: When releasing the attracting material, the voltage applied to the magnet coil is reversed in polarity and a reverse current of a fraction of the rated current is passed for a short time to reduce the residual magnetism of the McNette to zero, and the attracting material (magnetic Although the body has been devised so that it can be reliably separated, the appropriate applied voltage switching timing has not been set for the material, and in short, the operability during suction and release is both satisfactory. Hard to say. The present invention is intended to solve the drawbacks of deficiency, and its purpose is to use a power transistor having a self-extinguishing ability, and to automatically set the excitation characteristic (switching time) at the time of attraction and release. The purpose of this is to properly correct and improve the operability of the lifting magnet.

[0004]

SUMMARY OF THE INVENTION The present invention is a rectifying power supply Re.
c, a smoothing capacitor C ₂ connected in parallel thereto, a dropper circuit Drc including a pulse width modulation circuit PWM connected in series to a DC power supply, and a capacitor C ₁ connected in parallel to the DC power supply. Power transistors Tr ₁ , Tr ₂ , T connected in parallel to bridge-connected diodes D ₁ , D ₂ , D ₃ , D ₄ , respectively.
A bridge control circuit BCC composed of r ₃ and Tr ₄ , a free-wheeling diode D ₆ connected in parallel to the DC power source in the reverse direction, and a series connection to the dropper circuit between the diode D ₆ and the capacitor C _1. The connected smoothing reactor CH and the current detector CT at the midpoint of the control circuit BCC.
And a lifting magnet LM connected via a switch and a signal from the current detector to actuate by an operation switch Sw so that each base B ₁ , B ₂ ,
A drive circuit DCC for sending signals to B ₃ and B ₄ , and a main control circuit MCC for controlling the pulse width modulation circuit, and a DC power supply having a smoothing capacitor C ₁ connected in parallel to a rectification power supply Rec. , Diodes D ₁ , D ₂ , D connected in parallel to the DC power source and bridge-connected
Power transistors Tr connected in parallel to ₃ and D ₄ , respectively
_{1. A} bridge control circuit BCC composed of ₁ , Tr ₂ , Tr ₃ , Tr _4; a lifting magnet LM connected to a midpoint of the control circuit via a current detector CT; and an operation switch receiving a signal from the current detector. And a drive circuit DCC which is operated by the above-mentioned power transistor and sends a signal to each base B ₁ , B ₂ , B ₃ , and B ₄ of each power transistor, and the operation switch Sw which controls the drive circuit according to the detection value of the current detector. This is solved by a configuration including a main control circuit MCC and a pulse width modulation circuit PWM which receives a signal from the main control circuit and is inserted on the suction side of the main control circuit.

[0005]

Embodiment 1 Hereinafter, with reference to the drawings, the specific construction of an embodiment of the present invention will be described in detail. FIG. 1 is an electrical connection diagram of a contactless control circuit for operating a lifting magnet according to the present invention, FIG. 2 is an excitation characteristic when the operation switch of the magnet is on the attraction side, and FIG. 3 is the same when it is on the release side. In FIG. 1, Rec is a rectifying power source for full-wave rectifying three-phase alternating current by each rectifier to obtain a DC voltage V ₂ , C ₂ is a smoothing capacitor connected in parallel to the power source Rec, Drc blocks a reverse voltage to a transistor Tr ₅ described later and returns it to a capacitor C ₂ and a protection diode D ₅ and the transistor Tr _5.
5 , PWM is a pulse width modulation circuit, which includes a checker circuit formed by the transistor Tr ₅ to reduce the voltage V ₂ . D ₆ is a free-wheeling diode that blocks a reverse current from a smoothing reactor CH described later, C ₁ is a capacitor that absorbs a voltage generated when the lifting magnet is released, which will be described later, and B
CC is a power transistor Tr or power MOSFE
T (MOS type field effect transistor) or IGBT
(Insulated gate bipolar transistor) is a bridge control circuit in which diodes D ₁ , D ₂ , D ₃ and D ₄ are connected in parallel, and B ₁ , B ₂ ,
B ₃ and B ₄ are bases of the power transistors,
The LM is connected to the middle point of the bridge control circuit BCC via a current detector CT by a lifting magnet, and outputs the detected value as a current signal to a main control circuit described later. The MCC issues a voltage switching signal to the pulse width modulation circuit PWM according to a current signal from the current detector CT, and a drive circuit for giving a signal to each gate B ₁ , B ₂ , B ₃ and B ₄ of the power transistor. A main control circuit that also controls the DCC, Sw is an operation switch of the main control circuit MCC, and 1 indicates a position to be operated when the lifting magnet LM is attracted and 2 when it is released.

[0006]

[Embodiment 2] This circuit configuration is obtained by omitting a part of the circuit configuration shown in FIG. 1 described above. The same portions as those shown in FIG. The structural features will be described with reference to FIG. 4. The smoothing capacitor C ₂ , the dropper circuit Drc, the freewheeling diode D ₆ and the smoothing reactor CH in FIG. 1 are removed, and the output of the rectified power supply Rec is converted to the capacitor C ₁ . Directly connected points and the pulse width modulation circuit PWM to the main control circuit MCC
1 in that it is connected to the suction signal side a of FIG.

[0007]

The present invention has a ridge structure, and the operation and effect based on the structure will be described with reference to the drawings. In FIG. 1, the three-phase AC power supply is rectified by the rectification power supply Rec. We have a DC power supply, and first, the operation switch S
Before w is turned on as shown in the figures, the transistor Tr ₅ for the chipper is approximately 100% by the pulse width modulation circuit PWM.
It is controlled by the conduction angle of V and there is no voltage drop at this point.
₂ = V ₁ . Next, when the operation switch Sw is set to 1 and set to the suction side, a signal is issued from the main control circuit MCC to the drive circuit DCC and a base signal is sent to B ₁ and B ₄ , so that the power transistor of the bridge control circuit BCC is supplied. Tr ₁ and Tr ₄ become conductive, so that the current I ₁ flows in the direction of power transistor Tr ₁ → current detector CT → lifting magnet LM → power transistor Tr ₄ at this time, in FIG. 2, the current I ₁ reaches point P. When it rises, the current I ₁ is detected as a current signal by the current detector CT, and the main control circuit MCC sends a voltage switching signal to the pulse width modulation circuit PWM and the transistor Tr
The conduction angle of ₅ is reduced to control the DC voltage V ₁ stored in the capacitor C ₁ to be equal to the coil rated current Is of the lifting magnet LM.

Further, after the suction is completed, the operation switch Sw is set to 2
And the release side, the base signals B ₁ , B ₄
Is turned off, and at this time, the energy accumulated in the coil of the lifting magnet LM becomes I _{2 as} shown by the dotted line in FIG. 1 and is released to the power supply side, so that the diode D ₃ → the capacitor C ₁ → the diode D ₂ → The capacitor C ₁ is charged by the current I ₂ passing through the flow path of the current detector CT → the coil of the lifting magnet LM, and the DC voltage V ₁ temporarily rises. With respect to the voltage increase value at the time of release, a desired voltage can be obtained by selecting the electrostatic capacitance of the capacitor C ₁ . The current I ₂ at the time of release, when becomes substantially zero, in order to erase the residual magnetism (cancellation), during suction and reverse current I _{3 (FIG.} 1) in the bit flow purposes, the power transistor Tr _2, The base signals B ₂ and B are applied to Tr _3.
3 is turned on to turn on each transistor, and this current is I
Judged by the main control circuit MCC that a _third value (Fig. 3) by a signal current from the current detector CT, to turn off the base signal _B 2, _{B 3} of the power transistor _Tr 2, Tr _3. Since it operates like this, at the time of the next suction, the voltage V ₀ increased due to the energy absorption at the time of release.
Since a high voltage of max (FIG. 3) is applied to the coil, the current rises quickly.

In summary, the power transistors Tr ₁ and Tr ₄ are turned on at the time of suction, and the current I at that time is
_The current detector CT detects that ₁ has reached the current value P,
The main control circuit MCC sends a voltage switching signal to operate the pulse width modulation circuit PWM to lower the voltage in the checker circuit by the transistor Tr ₅ so that the rated voltage of the coil of the lifting magnet LM becomes the circuit voltage V.
₁ to control the power supply voltage V ₂ = V ₁ . When the current value at this time rises and reaches point P, the conduction angle of the transistor Tr ₅ is narrowed down and the pulse width modulation circuit PMW is operated and controlled so that the circuit voltage V ₁ drops to the rated voltage of the coil. On the other hand, at the time of release, the reverse current I ₂ flows due to the counter electromotive force generated when the current is turned off in the coil, the capacitor C ₁ absorbs the energy and the voltage rises, and this voltage V ₀ max keeps a high voltage until the next coil suction, and accelerates the current I ₁ at the time of suction so that the energy stored at the time of release can be effectively used at the next suction to accelerate the current rise. The operability of the lifting magnet LM can be improved, and an excellent effect capable of sufficiently achieving the intended purpose of the present invention can be expected.

Next, the function and effect based on the configuration shown in FIG. 4 described as the second embodiment will be described with reference to FIG. 5 showing the operating characteristics when the lifting magnet LM is attracted. The lifting magnet for the DC power supply V ₁ is eliminated by eliminating the chopper circuit by the power transistor Tr ₅ that is the dropper circuit Drc in the illustrated one and using the signal at the time of attraction by the bridge control circuit BCC as a pulse width modulation signal to control the conduction angle. L
The value of the voltage V ₀ across M is adjustable.

That is, in the initial stage of suction (see FIG. 5), the pulse width modulation circuit PWM is not operated and the conduction angle is set to 100.
[%], The above voltages are related to each other by V ₁ = V ₀ ,
The rising current I ₁ at the time of suction is made swift so that the current I ₁
When the point P reaches the point P, the main control circuit MCC sends a signal to the pulse width modulation circuit PWM to pulse-width modulate the suction signal. For example, the ON time T ₁ is 80% and the OFF time T ₂ is 20%.
% Signal, the voltage V ₀ across the lifting magnet LM is about 0.8 times the DC voltage V ₁ , that is, V ₀ ≈0.
Since the voltage is 8V ₁ , the rated current can be maintained and the coil can be prevented from being burnt. In short, the ratio between the conduction angles T ₁ and T _{2 in} the pulse width modulation is determined and the current is controlled so that the rated current Is of the retin magnet LM is obtained. Further, for the convenience of the pulse width modulation circuit PWM, when there is no signal from the main control circuit MCC, the same effect can be obtained by setting V ₀ ≈0.95V ₁ and receiving a signal such that V ₀ ≈V _1. can get. Incidentally, the signal frequency of the pulse width modulation circuit PWM has a large inductance of the coil even at a low frequency of tens to hundreds of cycles, so that the ripple of the current does not become large and causes no practical problem.

By adopting the configuration shown in FIG. 4 described above, a: If a chipper circuit is provided, the device becomes larger and the cost becomes higher than that shown in FIG. B: The circuit configuration becomes complicated. C: Noise and radio waves are generated from the chipper circuit, which adversely affects various communication equipment such as radios. The above problems can be solved, an economically ideal contactless control circuit for a lifting magnet can be provided, and an excellent effect capable of sufficiently achieving the intended purpose of the present invention can be expected.

[Brief description of drawings]

FIG. 1 is an electrical connection diagram of a contactless control circuit showing an embodiment according to the present invention.

FIG. 2 is an excitation current characteristic diagram when the operation switch of FIG. 1 is set to the attraction side.

FIG. 3 is an exciting current characteristic diagram when the operation switch of FIG. 1 is set to the release side.

FIG. 4 is an electrical connection diagram of a contactless control circuit showing a different embodiment according to the present invention.

FIG. 5 is an excitation current characteristic diagram showing an enlarged period of a pulse width modulation signal when the operation switch of FIG. 4 is set to the attraction side.

[Explanation of symbols]

B ₁ , B ₂ , B ₃ , B ₄ Base (gate) BCC bridge control circuit C ₁ capacitor C ₂ smoothing capacitor CH smoothing reactor CT current detector D ₁ , D ₂ , D ₃ , D ₄ diode D ₅ protection Diode D ₆ freewheeling diode Drc dropper circuit DCC drive circuit LM lifting magnet MCC main control circuit PWM pulse width modulation circuit Rec rectification power supply Sw operation switch Tr ₁ , Tr ₂ , Tr ₃ , Tr ₄ power transistor or power MOSFET or IGBT V ₁ DC voltage (circuit voltage) V ₂ Power supply voltage (DC voltage) V ₀ Voltage across lifting magnet Is Rated current of lifting magnet

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[Procedure amendment]

[Submission date] July 31, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

That is, in the initial stage of suction (see FIG. 5), the pulse width modulation circuit PWM is not operated and the conduction angle is set to 100.
[%], The above voltages are related to each other by V ₁ = V ₀ ,
The rising current I ₁ at the time of suction is made swift so that the current I ₁
When the point P reaches the point P, the main control circuit MCC sends a signal to the pulse width modulation circuit PWM to pulse-width modulate the suction signal. For example, the ON time T ₁ is 80% and the OFF time T ₂ is 20%.
% Signal, the voltage V ₀ across the lifting magnet LM is about 0.8 times the DC voltage V ₁ , that is, V ₀ ≈0.
Since the voltage is 8V ₁ , the rated current can be maintained and the coil can be prevented from being burnt. In short, the ratio between the conduction angles T ₁ and T _{2 in} the pulse width modulation is determined and the current is controlled so that the rated current Is of the retin magnet LM is obtained. For the convenience of the pulse width modulation circuit PWM, if an example is given, if there is no signal from the main control circuit MCC , 100% on the transmission circuit.
If it is difficult to set, it is possible to obtain the same effect by setting V ₀ ≈0.95V ₁ and setting V ₀ ≈ (0.95 × 0.8) V ₁ when receiving a signal. Incidentally, the signal frequency of the pulse width modulation circuit PWM has a large inductance of the coil even at a low frequency of tens to hundreds of cycles, so that the ripple of the current does not become large and causes no practical problem.

Claims (2)

[Claims] 1. A DC power supply including a smoothing capacitor C ₂ connected in parallel to a rectifying power supply Rec, a dropper circuit Drc including a pulse width modulation circuit PWM connected in series to the DC power supply, and a DC power supply connected in parallel to the DC power supply. bridge-connected diodes _D 1 comprises a capacitor _{C 1} has,
A bridge control circuit BCC including power transistors Tr ₁ , Tr ₂ , Tr ₃ , Tr ₄ connected in parallel to D ₂ , D ₃ , and D ₄ , respectively, and a freewheeling diode connected in parallel to the DC power source in a reverse direction. D ₆ , a smoothing reactor CH connected in series with the dropper circuit between the diode D ₆ and the capacitor C _1, and the control circuit BCC.
A lifting magnet LM tied through the current detector CT at the midpoint of each base B ₁ of each of power transistors operated by the operation switch receives a signal from the current _{detector, B 2, B 3, B} 4 And a main control circuit MCC including the operation switch Sw for controlling the pulse width modulation circuit and a drive circuit DCC for sending a signal to the contactless control circuit of the lifting magnet. 2. A DC power supply having a smoothing capacitor C ₁ connected in parallel with a rectification power supply Rec, and diodes D ₁ , D ₂ , D connected in parallel with the DC power supply and bridge-connected.
Power transistors Tr connected in parallel to ₃ and D ₄ , respectively
_{1. A} bridge control circuit BCC composed of ₁ , Tr ₂ , Tr ₃ , Tr _4; a lifting magnet LM connected to a midpoint of the control circuit via a current detector CT; and an operation switch receiving a signal from the current detector. And a drive circuit DCC which is operated by the above-mentioned power transistor and sends a signal to each base B ₁ , B ₂ , B ₃ , and B ₄ of each power transistor, and the operation switch Sw which controls the drive circuit according to the detection value of the current detector. A contactless control circuit for a lifting magnet, comprising a main control circuit MCC and a pulse width modulation circuit PWM which receives a signal from the main control circuit and is inserted on the suction side of the main control circuit. .