JP2000100620A - Method for preventing freezing for electromagnetic lock device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent freezing of an electromagnetic lock device in a simple method. SOLUTION: A bobbin 3 to be housed in a case body 2 is arranged in a lock device 1, and two coils, that is, a start coil 5 and a holding coil 6 are wound around the bobbin 3. At the time of preventing freezing, voltages whose magnetomotive forces are equal and whose directions are opposite are impressed to the start coil 5 and the holding coil 6. Thus, the magnetomotive forces generated in the start coil 5 and the holding coil 6 are offset so that a movable iron core 10 can be maintained at a lock position projected from the case body 2 without being operated. Heating is generated at the start coil 5 and the holding coil 6 according to the impression of the voltages so that the movable iron core 10 can be heated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the prevention of freezing of an electromagnetic lock device, and more particularly to a method of easily preventing freezing with two coils.

[0002]

2. Description of the Related Art Heretofore, this type of electromagnetic lock device has been used for a fall prevention device in a multistory parking lot or the like to prevent the device from falling.

As shown in FIG. 7, for example, such an electromagnetic lock device 50 includes an exciting coil 52 wound around a cylindrical bobbin 51, and a fixed magnetic pole 53 projecting in the shape of a truncated cone around the center of the exciting coil 52. A movable core 57 having a magnetic pole portion 56 having a conical trapezoidal hole on the side facing the lock end portion 55 that enters and exits and the fixed magnetic pole 53, and a movable core 57 provided between the fixed magnetic pole 53 and the movable core 57. And the position detecting switch 5 of the movable iron core 57.
9 and is covered with a main body container 60 having a watertight structure.

[0004] This electromagnetic lock device 50 generally comprises
The linear movement distance (stroke) of the movable iron core 57 is large,
For example, the movable iron core 57 is formed to have a stroke of about 40 mm, and is mounted on a column, a girder member, or the like of an outdoor or indoor multilevel parking lot with the axis of the movable iron core 57 horizontal. When the lock end 55 of the movable iron core 57 projects, the lock end 5
5 is provided so as to be able to support an elevating pallet that falls for some reason, and has been used to prevent the pallet from falling.

[0005]

However, in the conventional lock device, the excitation coil is not normally energized, but is energized when the movable iron core is attracted and moved into the case. When used in a cold region, the movable core freezes, and the movable core is not attracted and moved even when the excitation coil is excited, or even when the excitation coil is de-energized, the movable core is in a predetermined position. There is a fear that it will not protrude. If the movable iron core freezes, it will lead to malfunction, and its function cannot be performed despite being used as a fall prevention in a multi-story parking lot. Therefore, an externally mounted heater is required as a measure to prevent freezing, which not only complicates the operation but also increases the cost.

The present invention has been made in view of the above, and an object of the present invention is to provide a method for preventing freezing of an electromagnetic lock device which can easily prevent freezing.

[0007]

SUMMARY OF THE INVENTION A method for preventing freezing of an electromagnetic lock device according to the present invention is performed as follows to solve the above-mentioned problems. That is, it has an excitation coil disposed in a case body and wound around a cylindrical bobbin, and a movable core disposed in the bobbin, and the movable core projects from the case body by the excitation coil. A method for preventing freezing of an electromagnetic lock device configured to move in an axial direction between a lock position and a suction position stored in the case body, wherein the excitation coil includes a first coil and a second coil, The movable iron core is configured to be attracted and moved by excitation of the first coil and the second coil, and when the movable iron core is at the lock position, the first coil and the By applying voltages having the same magnetomotive force to the second coil in opposite directions to each other, the first coil and the front machine base 2 coil generate heat without attracting and moving the movable iron core. It is intended to.

Preferably, the bobbin has a cylindrical bottom wall and a front wall, an intermediate wall, and a rear wall extending from the bottom wall in an outer radial direction to form two chambers. The first coil and the second coil are wound around the chamber, and a voltage is applied separately to each other.

The bobbin has a cylindrical bottom wall, a front wall extending rearward from the bottom wall, and a rear wall, and is formed between the front wall and the rear wall. The first coil and the second coil are wound with a spacer interposed between the first coil and the second coil, and voltages are separately applied to the first coil and the second coil, respectively. It may be something.

[0010] More preferably, when the movable iron core is attracted, a voltage in the same direction is applied to the first coil and the second coil, and the magnetomotive force of the first coil is reduced by the magnetomotive force of the second coil. It is more preferable that the voltage is set to be larger than the magnetomotive force and the voltage is set so that only the voltage of the second coil is continuously applied in a state where the movable iron core is attracted.

Further, if the first coil and the second coil have a circuit configured in parallel, and each coil is selectively connected to a freezing prevention relay, it is preferable that the first coil and the second coil are selectively connected to a freezing prevention relay. Good.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

In the following description, an electromagnetic lock device (hereinafter referred to as a lock device) is provided with two coils to separately apply a voltage to prevent freezing. Other functions besides the antifreeze function may be used.

For example, the electromagnetic lock device 1 of the first embodiment
Has two coils that are compact and have a function of reducing power consumption in addition to an adsorption action and an antifreeze action, and are formed in a cylindrical shape as shown in FIG. A case body 2, a bobbin 3 disposed in the case body 2, having a hollow shape and having an intermediate wall facing outward, formed in two chambers, and a first coil wound around each chamber of the bobbin 3. An exciting coil 4 composed of a starting coil 5 and a holding coil 6 as a second coil, and a movable core 10 which is slidably arranged in the bobbin 3 and whose tip is formed to be protrudable from the case body 2. It is configured to have. The first coil and the second coil are not limited to the starting coil 5 and the holding coil 6 described below, but may be any as long as two coils are provided. Further, the locking device described below is not limited to the following.

In the following description, when the movable core 10 is at a position protruding from the case body 2, it is called a lock position, and when it is at a position housed in the case body 2, it is called a suction position.

The case body 2 has a stepped portion on the tip side (left side in FIG. 1) for mounting on the body to be mounted.
0, a case front part 21 formed to enter and exit, a case rear part 22 formed in a disk shape on the rear end side (right side in FIG. 1), and a case front part 21 and a case rear part 22 connected to form a cylindrical shape. A pipe 8 for slidingly guiding the movable iron core 10 is fixedly supported on the inner peripheral surfaces of the case front part 21 and the case rear part 22. The case front portion 21, the case rear portion 22, and the case body portion 23 are all formed of a magnetic material, and form a magnetic path between the case body 2 and the movable iron core 10 by energizing the excitation coil 4. In addition, a hole 21a for the movable iron core 10 to enter and exit is formed in the front part 21 of the case.
Are formed, and a plurality of female screws 21b are formed on the step portion along the axial direction from the front end side to the rear end side.

The bobbin 3 has a cylindrical bottom wall 31 and a front wall 32.
Two coil chambers are formed having an intermediate wall 33 and a rear wall 34, and the front wall 32 is disposed so as to abut and support the rear end face of the case front part 21, and among the two coil chambers, The starting coil 5 is wound around the front coil chamber, and the holding coil 6 is wound around the rear coil chamber.

When the movable core 10 is attracted, the starting coil 5 is arranged to extract a large attractive force when the movable core 10 is started, and its magnetomotive force is set to be larger than that of the holding coil 6. Holding coil 6 for generating magnetomotive force of starting coil 5
By making it larger than the magnetomotive force of
A leakage magnetic flux Φ1 is generated between a magnetic flux generated around the starting coil 5 and a magnetic flux generated around the holding coil 6, and the leakage magnetic flux Φ1 can be caused to flow around the starting coil 5.

When the movable core 10 is in the locked position,
When freeze prevention is performed, the starting coil 5 and the holding coil 6 are set so as to apply voltages having the same magnetomotive force in opposite directions. When freeze prevention is not performed, the voltage is applied to the startup coil 5 and the holding coil 6. It is set not to be applied.

One limit switch wall 3 extends axially from the rear wall 34 of the bobbin 3 toward the case rear 22.
5 is formed, and the limit switch 36 is mounted so that the movable core 10 can be detected. Limit switch 3
An operator 36 a is disposed in 6, and a tip of the operator 36 a is located in the pipe 8 through a notch hole 8 a formed in the pipe 8.

The movable iron core 10 is formed in a two-stage cylindrical shape having a small-diameter lock portion 11 and a large-diameter slide portion 12, and the lock portion 11 is arranged so as to protrude outward from the case body 2. It is formed long so as to have a stroke of about 50 mm, and is movably fitted to a packing 25 mounted in a hole 21 a of the case front part 21. The sliding portion 12 is formed shorter than the lock portion 11 and slides inside the pipe 8 to form a hollow portion 12a therein. Sliding part 12
The gap between the sliding portion 12 and the case rear portion 22 needs to be large in order to secure the sliding stroke of the movable iron core 10. In this embodiment, the lock portion 11 of the movable iron core 10 is in the locked position outside the case body 2. At one time, that is, the exciting coil 4
Is not energized, the distance (axial gap) S1 from the rear end surface of the sliding portion 12 of the movable iron core 10 to the front end surface of the case rear portion 22 is equal to the distance between the outer peripheral surface of the sliding portion 12 and the inside of the case body portion 23. It is set larger than the peripheral surface (gap in the radial direction) S2. Accordingly, when the movable iron core 10 is started, the magnetic flux generated by the excitation of the starting coil 5 and the holding coil 6 flows in the radial direction with a smaller gap than in the axial direction.

On the other hand, a rubber-like elastic stopper 26 projecting from the center of the axial center is fixed to the inner end face of the case rear part 22, and the rear end face of the sliding part 12 of the movable core 10 is
6. A return spring 27 is disposed between the hollow portion 12a of the sliding portion 12 of the movable core 10 and the stopper 26 so as to bias the lock portion 11 of the movable core 10 outward from the case front portion 21. ing. Further, the front end of the case 21
An elastic cushioning member 28 is fixed to the inner end face of the sliding member 12, and the front end face of the sliding portion 12 abuts on the cushioning member 28 when the movable core 10 reaches the most distal end position.

Therefore, in the lock device 1 having the above-described structure, the sliding portion 12 of the movable iron core 10 is short, and the entire device can be made compact accordingly. Moreover, the stroke of the movable iron core 10 does not change. Furthermore, since the tapered portion is not formed as compared with the conventional movable iron core, the processing cost can be reduced,
Further, since the conventional tapered fixed magnetic pole is not formed, the processing cost can be reduced also in the case rear portion 22.

Next, the lock device 1 thus configured
Will be described.

In a normal state where the freezing prevention is not performed, when the starting coil 5 and the holding coil 6 are not energized, the movable iron core 10 causes the sliding portion 1 to move by the urging force of the return spring 27.
The front end face 2 is positioned in contact with the cushioning member 28, and the lock portion 11 is at a lock position protruding from the case front portion 21.

In order to prevent freezing, a control panel (not shown) operates an operation switch for "freezing prevention" so that a voltage having the same magnetomotive force is applied to the starting coil 5 and the holding coil 6 in opposite directions. Is applied. Since the magnetomotive forces of the starting coil 5 and the holding coil 6 cancel each other, the lock portion 11 remains held at the lock position protruding from the case front portion 21. However, since the two coils of the starting coil 5 and the holding coil 6 are energized, the two coils generate heat and are transmitted to the movable core 10 to warm the movable core 10. Therefore, even if the external temperature is low, the movable iron core 10 itself does not freeze because it is heated. In any case, the limit switch 36 detects that the movable iron core 10 is in a non-pressed state apart from the actuator 36a, and that the lock portion 11 is in the lock position.

Next, when attracting the movable iron core, a voltage is applied to the starting coil 5 and the holding coil 6 in the same direction and the starting coil 5 has a larger magnetomotive force than the holding coil 6. As a result, a magnetic circuit is formed between the case body 2 and the movable iron core 10, and a magnetic force acts to attract the movable iron core 10 to the suction position side. As shown in FIG. 1, the magnetic flux Φ generated at this time depends on the magnetic flux generated around the starting coil 5 and the holding coil 6.
Of the magnetic flux Φ2 which flows between the case body 2 and the movable core 10 due to the combination of the magnetic flux generated around and the leakage magnetic flux Φ1 generated by the difference in the magnitude of the magnetomotive force between the starting coil 5 and the holding coil 6 described above. As for the attraction force, the attraction force at the time of starting increases as compared with the case where the starting coil 5 and the holding coil 6 have the same magnitude of the magnetomotive force.

This attractive force overcomes the urging force of the return spring 27, and as shown in FIG.
Move to side 2. At this time, the lock portion 1 of the movable core 10
1 is substantially flush with the front end surface of the case front portion 21. This stroke is set to about 40 to 50 mm. When the movable iron core 10 moves to the case rear part 22 side, the operator 36a of the limit switch 36 is pressed against the outer peripheral surface of the sliding part 12 of the movable iron core 10 to operate the limit switch 36. Since the limit switch 36 is a normally closed circuit (b contact), when the actuator 36a is pressed and activated, the limit switch 36 is turned off.
As a result, the starting coil 5 is cut off and de-energized, and only the holding coil 6 is energized. The magnetic flux generated at this time flows from the front part 21 of the case to the rear part 22 of the case through the movable core 10, and holds the movable core 10 at the suction position.

This state will be described with reference to a circuit diagram shown in FIG.
The AC power supply 15 is connected to the input terminal of the full-wave rectifier circuit 16, and the starting coil 5 and the holding coil 6 are connected in parallel to the output terminal of the full-wave rectifier circuit 16. The starting coil 5 includes
The anti-freeze operation relay R1 and the normal operation relay F1 that does not perform anti-freeze are selectively connected in parallel, and the normal operation relay F1 is connected to the starting coil 5 so that a current flows in the forward direction. A resistor r is connected in series to the anti-freezing relay R1 and the anti-freezing relay R
When a current flows through the relay 1, the anti-freezing relay R1 is connected so that the current flowing through the starting coil 5 is in the opposite direction to that during normal operation. In addition, a freezing prevention relay R2 and a normal operation relay F2 are selectively connected in parallel to the holding coil 6, and both the antifreezing relay R2 and the normal operation relay F2 have a forward current flowing through the holding coil 6. It is connected to flow in the direction. The anti-freeze relays R1, R2 and the normal operation relays F1, F2 are switched by a changeover switch SW.

Further, a relay F3 operated by turning on and off the limit switch 36 is connected between the starting coil 5 and the holding coil 6. Limit switch 36
Means that the circuit is closed and the relay F3 is ON when the power is ON
When the armature 36a of the limit switch 36 is pressed by the movable iron core 10, the relay F3 is turned off and the starting coil 5
Is connected so as to cut off the circuit.

Therefore, during normal operation, when the power supply 15 is turned on, the alternating current is converted into direct current by the full-wave rectifier circuit 16, and the direct current passes through the normal operation relays F1 and F2 and the starting coil 5 and the holding coil 6 are turned on. Flows in the forward direction. When the starting coil 5 and the holding coil 6 are energized to move the movable core 10, the limit switch 36 is released and the holding coil 6 is released.
Is kept closed, the holding coil 6 is energized, and the circuit of the starting coil 5 is released, so that the excitation of the starting coil 6 is released. Note that the magnetic force due to the energization of the holding coil 6 is set slightly larger than the urging force of the return spring 27, and its power consumption and heat generation are smaller than those in the related art.

The limit switch 36 performs the function of self-switching between start and hold as described above. However, by providing another wiring to the contact a, the limit switch 36 functions as a sensor for confirming the operation from the outside. Can be fulfilled.
For example, a lamp is connected to the a contact and the limit switch 36
When the lamp is turned on from the contact b to the contact a by pressing the actuator 36a, the locking portion 1 of the movable core 10
It can be confirmed that 1 is at the suction position stored in the case body 2. Therefore, it is not necessary to provide a new sensor for confirming the locked position or the attracted position of the movable iron core 10.

When the energization of the holding coil 5 is stopped, the magnetic field generated between the case body 2 and the movable core 10 is demagnetized, and the movable core 10 is moved by the urging force of the return spring 27 to the lock position where the lock portion 11 protrudes. Return.

This return movement is cushioned by the cushioning member 28, so that the generation of metal noise can be prevented.

To prevent freezing, when "freezing prevention" of the control panel (not shown) is turned on, the switch SW switches to the antifreezing relays R1 and R2, and the current converted from the full-wave rectifier circuit 16 into a DC current is On the one hand, it flows in the reverse direction to the starting coil 5 through the relay R1, and on the other hand, flows in the forward direction to the holding coil 6 through the anti-freezing relay R2.

On the other hand, the starting coil 5 and the holding coil 6
Since the voltages are applied to the two coils so that the magnetomotive forces become equal, the magnetomotive forces of the two coils generated in the opposite directions cancel each other, and the movable iron core 10 is not moved.
However, since a voltage is applied to the starting coil 5 and the holding coil 6 as described above, the starting coil 5 and the holding coil 6
Is generated and is transmitted to the movable iron core 10.

The lock device 1 configured as described above
For example, as shown in FIG. 4, it is used as a lock device for preventing a pallet from falling up and down in a multistory parking lot.

In FIG. 4, the lock device 1 is provided with female screws 21b of the front part 21 of the case to the beam members 40 on both sides of the multi-story parking lot.
Are fixed using bolts 39, and are electrically connected to a control panel (not shown).

In the non-energized state of the starting coil 5 and the holding coil 6, the movable core 10 is urged by the return spring 27 in the non-attracted state, and the lock portion 11 protrudes inward of the both girder members 40. In particular, when the temperature drops in a cold region, the freezing prevention is activated to warm the movable iron core.

The beam members 40, 40 arranged on both the left and right sides,
Due to the protrusion of the lock portions 11 of the two lock devices 1, the lower surface of the lifting pallet 41 that falls for some reason is
Each lock portion 11 can be stopped by contacting the upper surface.

When the lifting pallet is moved up and down, the starting coil 5 and the holding coil 6 are energized.
The movable core 10 is sucked into the case body 2 and the movable core 10
The rear end surface of the sliding portion 12 and the stopper 26 abut against each other, the lock portion 11 is moved to a position flush with the front portion 21 of the case, only the activation coil 5 is de-energized, and the excitation of the holding coil 6 Maintain the adsorption state. Then, the next operation set for the lifting pallet 41 is started.

FIG. 5 shows a lock device 70 of a second embodiment, in which a bobbin 71 is formed having a bottom wall 72, a front wall 73, and a rear wall 74. , Rear wall 7
An exciting coil 75 formed by a first coil 77 and a second coil 78 is wound in a chamber formed between the four coils, and a spacer 79 is sandwiched between the first coil 77 and the second coil 78. Have been. The first coil 77 and the second coil 78 are formed to have the same wire diameter and the same number of turns. When the movable core 10 is attracted, the same voltage in the same direction is applied to the first coil 77 and the second coil 78, To prevent freezing at the position where the movable core 10 is projected to the lock position, the first coil 77 and the second coil
The same voltage in the opposite direction is applied to the coil 78. Note that, even if the number of turns and the wire diameter of the first coil 77 and the second coil 78 are not the same, a voltage may be applied so that the magnetomotive forces are equal. In the circuit of this embodiment, FIG.
Can be eliminated.

Since the lock device 70 does not reduce power consumption in particular, the first coil 77 and the second coil 78
May not correspond to the starting coil 5 and the holding coil 6 in the first embodiment. Of course, it may have the same function as the starting coil 5 and the holding coil 6. This type of locking device 70 is compact.

In this lock device 70, FIG.
As shown in (1), the bobbin 71 may have an intermediate wall 75a and be formed in two chambers as in the first embodiment. In this case, the first coil 77 is provided in one chamber with the second coil 78.
Are separately mounted in the other room, and the spacer 79 is omitted.

The method for preventing freezing of the lock device according to the present invention is not limited to the lock devices of the first and second embodiments since the two coils are formed and separately excited as described above. . For example, the conventional lock device 5 shown in FIG.
The starting coil 52 disposed at 0 may be divided into two parts via a spacer. Then, a voltage having the same magnetomotive force may be applied to each of the divided excitation coils to prevent freezing, so that the voltages are opposite to each other.

The respective lock devices described above are not limited to those described above, and the form of each part can be changed without changing the gist thereof. For example, if a fixed magnetic pole that fits into the hollow portion 12a of the movable core 10 is provided in the case rear portion 22 so as to protrude inward of the case, the movable core 10
Can be guided stably.

[0047]

As described above, according to the present invention, a method for preventing freezing of an electromagnetic lock device is provided by providing an exciting coil provided in a case body and wound on a cylindrical bobbin, and provided in the bobbin. A movable iron core, wherein the movable iron core is configured to move in the axial direction between a lock position protruding from the case body by the excitation coil and a suction position housed in the case body. Applied to a lock device, wherein the exciting coil includes a first coil and a second coil, and the movable core is attracted and moved by excitation of the first coil and the second coil. And when the movable iron core is in the locked position,
By applying voltages having the same magnetomotive force to the first coil and the second coil in opposite directions to each other, the starting coil and the holding coil generate heat without attracting and moving the movable core. Therefore, freezing can be prevented by the electromagnetic lock device itself. Therefore, there is no need to dispose a heater externally as in the related art, and it is possible to provide an easy and low-cost lock device.

In the electromagnetic lock device freezing prevention method, when the movable iron core is attracted, a voltage in the same direction is applied to the first coil and the second coil, and the voltage of the first coil is reduced. An electromagnetic lock device of a type in which the magnetomotive force is set to be larger than the magnetomotive force of the second coil and the voltage is set so that only the voltage of the second coil continues to be applied while the movable iron core is attracted, Freezing can be easily prevented by an electromagnetic lock device that can reduce the power.

Also, since the first coil and the second coil have a circuit configured in parallel and each coil is selectively connected to the anti-freezing relay, the anti-freezing operation is easily performed. And a simple start-up holding self-switching circuit can be configured.

[Brief description of the drawings]

FIG. 1 is a front sectional view of an electromagnetic lock device that employs the freeze prevention method of the present invention.

FIG. 2 is a front sectional view showing a state in which a movable iron core of the electromagnetic lock device is attracted.

FIG. 3 is a circuit diagram showing an excitation coil of the electromagnetic lock device of the present invention.

FIG. 4 is a diagram showing one use mode of the electromagnetic lock device of the present invention.

FIG. 5 is a front sectional view showing another electromagnetic lock device that employs the freeze prevention method of the present invention.

FIG. 6 is a partial sectional view showing another embodiment of the bobbin of FIG. 5;

FIG. 7 is a front sectional view showing a conventional electromagnetic lock device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electromagnetic locking device 2 ... Case body 3 ... Bobbin 4 ... Exciting coil 5 ... Starting coil (1st coil) 6 ... Holding coil (2nd coil) 10 ... Moving iron core 11 ... Locking part 12 ... Sliding part 21 ... Case front 22 ... Case rear 23 ... Case main body 36 ... Limit switch

Claims (5)

[Claims] 1. An excitation coil disposed in a case body and wound around a cylindrical bobbin, and a movable core disposed in the bobbin, wherein the movable iron core is moved by the excitation coil to the case body. A freezing prevention method for an electromagnetic lock device configured to move in an axial direction between a lock position protruding from a lock position and a suction position stored in the case body, wherein the excitation coil includes a first coil and a second coil. A coil, and the movable core is configured to be attracted and moved by the excitation of the first coil and the second coil. By applying voltages having the same magnetomotive force to the coil and the second coil in opposite directions to each other, the first coil and the front base 2 coil generate heat without adsorbing and moving the movable iron core. This And a method for preventing freezing of the electromagnetic lock device. 2. The bobbin includes a cylindrical bottom wall, a front wall, an intermediate wall, and a rear wall extending from the bottom wall in an outer radial direction to form two chambers. 2. The method for preventing freezing of an electromagnetic lock device according to claim 1, wherein the first coil and the second coil are wound around each other, and voltages are separately applied. 3. The bobbin is formed having a cylindrical bottom wall, a front wall extending rearward from the bottom wall in a radial direction, and a rear wall, between the front wall and the rear wall. The first coil and the second coil are wound with a spacer interposed between the first coil and the second coil, and voltages are separately applied to the first coil and the second coil, respectively. A method for preventing freezing of the electromagnetic lock device according to claim 1. 4. When attracting the movable core, a voltage in the same direction is applied to the first coil and the second coil, and the magnetomotive force of the first coil is reduced by the magnetomotive force of the second coil. 4. The voltage of the second coil is set to be larger than the voltage of the second coil while the movable iron core is attracted. 5.
A method for preventing freezing of the electromagnetic lock device according to the above. 5. A circuit according to claim 1, wherein said first coil and said second coil have a circuit configured in parallel, and each coil is selectively connected to a freeze prevention relay. 5. The electromagnetic locking device according to claim 3, 3 or 4.