Ultra-long stroke electromagnet structure

Abstract

The utility model relates to the field of electromagnets, in particular to an ultra-long stroke electromagnet structure which comprises an electromagnet frame, an armature, a restoring spring, permanent magnet sets, a coil set, a beat signal generator, a beat signal distributor and a driving module. The driving module controls on, off and direction change of current of the coil assembly according to a beat signal generated by the beat information module, the axis of each coil presents a magnetic state, a non-magnetic-pole state and a magnetic pole direction change state, and an electromagnetic field in the coil assembly generates electromagnetic force in the same direction on the permanent magnet assembly to push the armature to move. And the push-out formation of the armature only depends on the axial length of the armature and is not limited by the axial size of the coil assembly, so that the electromagnet with an ultra-long stroke can be produced according to the technical scheme of the utility model.

Description

Technical Field

[0001] The utility model relates to the field of electromagnets, and more specifically, to an ultra-long stroke electromagnet structure. Background Art

[0002] Electromagnets are widely used in industrial automation control. Ordinary push-pull electromagnets on the market use a single coil to directly energize to generate a constant electromagnetic field to attract the armature into the inner cavity of the coil, thereby driving the armature head end to be pushed out. The disadvantages of this method are: first, the stroke is limited by the axial length of the coil, generally not exceeding 70% of the axial length of the coil, making it impossible to make the stroke too long; second, its initial thrust decays as a quadratic function with the length of the stroke, and the initial stroke thrust is very weak. Therefore, ordinary push-pull electromagnets cannot achieve long strokes and high initial stroke thrusts. In some specific applications that require long strokes and high initial stroke thrusts, ordinary electromagnets are unable to meet their needs.

[0003] The prior art discloses a long-stroke low-temperature rise double-coil electromagnet. In order to solve the long-stroke problem, the electromagnet adopts the method of simultaneously powering the double coils in the early stage of the attraction, that is, increasing the ampere-turn value of the attraction process, so that the magnetic flux value inside the coil reaches the maximum, and the armature moves. When the armature is attracted, only the holding coil is powered to achieve the low ampere-turn attraction state. This method mainly realizes the long-stroke movement of the electromagnet by increasing the electric power to force the armature to move. Therefore, its stroke increase is still limited by the axial length of the coil, and it still has certain limitations in specific applications that require a long stroke and a large initial stroke thrust. Summary of the invention

[0004] The utility model aims to solve the problem that the stroke is limited by the axial length of the coil, and creatively designs an ultra-long stroke electromagnet structure.

[0005] In order to achieve the above-mentioned purpose, the utility model provides an ultra-long stroke electromagnet structure, including: an electromagnet frame, an armature, a restoring spring, a permanent magnet group, a coil group, a beat signal generator, a beat signal distributor and a driving module, wherein the permanent magnet group is composed of two end faces of its magnetic poles in the axial direction, and each single permanent magnet with opposite magnetic poles on each adjacent end face is arranged, and the permanent magnet group is axially distributed on the armature, and the coil group is composed of two groups of coils arranged in a mutually interlaced manner and sleeved on the outer periphery of the permanent magnet group, and the beat signal generator, the beat signal distributor and the driving module The block is connected to a DC power supply and a coil group, the pulse output end of the beat signal generator is connected to the input end of the beat signal distributor, the four output ends of the beat signal distributor are respectively connected to the four control input ends of the drive module, the four output ends of the drive module are respectively connected to the four ends of the coil group, the drive module controls the on / off and direction change of the two groups of coil currents of the coil group according to the high and low level changes of the output end of the beat signal distributor, the current of the coil group generates an electromagnetic force of a certain direction on the permanent magnet group, pushes the permanent magnet group and drives the armature to extend and move.

[0006] Furthermore, the beat signal generator and the beat signal distributor are composed of pure electronic circuits, or are composed of a position sensing strip that moves synchronously with the armature and a Hall switch fixedly mounted on the electromagnet frame. Furthermore, the core component of the signal generator composed of the electronic circuit is the time base chip NE555.

[0007] Furthermore, the core component of the beat signal distributor is a decimal counting chip CD4017.

[0008] Furthermore, the signal generator formed by the electronic circuit changes the period of the beat signal, thereby changing the speed of the on / off or direction change of the coil group current, thereby adjusting the speed of the armature pushing out.

[0009] Furthermore, the beat signal generator is composed of a first position sensing strip and a first Hall switch, the length of the first position sensing strip is similar to the length of the armature, and a plurality of separated first permanent magnets are distributed thereon, the spacing between each first permanent magnet is the same as the axial dimension of a coil, and the first position sensing strip is rigidly connected to the tail end of the armature, the first Hall switch is fixedly mounted on the electromagnet frame, the output end of the first Hall switch is connected to the signal input end of the beat signal distributor, each first permanent magnet on the first position sensing strip can form a proximity sense to the first Hall switch, when a first permanent magnet on the first position sensing strip is close to the first Hall switch, the first Hall switch outputs a high level to the signal input end of the beat signal distributor, so that the output states of the beat signal distributor change, thereby causing the control input end state of the driving module to change, and finally causing the on, off and direction of the coil group current to change.

[0010] Furthermore, the beat signal generator and the beat distributor are composed of a second position sensing strip and four second Hall switches, the second position sensing strip is axially distributed with a plurality of separated second permanent magnets, the spacing between each second permanent magnet is equal to the sum of the axial dimensions of the four coils, and the length of the second position sensing strip is close to the length of the armature, and is rigidly connected to the tail end of the armature, the four second Hall switches are fixedly mounted on the electromagnet frame, the spacing between the four second Hall switches is the same as the axial dimension of one coil, the four output ends of the four second Hall switches are respectively connected to the four control input ends of the driving module, when a second permanent magnet on the second position sensing strip approaches the four second Hall switches in turn, it will output a high level to the four control ends of the driving module in turn, completing the beat signal distribution function according to the actual push-out position of the armature, and ultimately causing the on, off and direction change of the coil group current.

[0011] Furthermore, the core component of the driving module is a full-bridge driving chip RZ7886.

[0012] Furthermore, the permanent magnet group on the armature is composed of separate permanent magnets arranged one by one, or the permanent magnet armature is made by magnetizing a high coercive force magnetic material rod in sections.

[0013] Furthermore, it also includes an armature terminal travel locking device, which includes a locking coil, a yoke, and a locking armature. The locking coil is installed at the rear end of the coil group, the yoke is arranged on the periphery of the locking coil, and the locking armature is arranged at the rear end of the armature.

[0014] Compared with the prior art, the beneficial effects of the technical solution of the utility model are:

[0015] 1. It adopts a unique structure. The thrust of the armature is determined by the radial area and magnetic induction intensity of the permanent magnet, the number of turns of the coil group and the current passing through. The initial thrust is large, which improves the defect of weak initial thrust of existing push-pull electromagnets on the market.

[0016] 2. With a unique structure, the length of the electromagnet's stroke is not limited by the axial length of the coil, meeting the requirements of some automatic control scenarios that require long-stroke industrial automation equipment.

[0017] 3. It can provide the market with a brand-new structure of ultra-long stroke push-pull electromagnet products. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a basic structural schematic diagram of the utility model;

[0019] Figure 2 It is a schematic diagram of the arrangement structure of the armature permanent magnet group and the coil group;

[0020] Figure 3 It is the functional block diagram of the control circuit;

[0021] Figure 4 It is a basic structural diagram of embodiment 1;

[0022] Figure 5 This is a driving control circuit diagram of Embodiment 1, in which 4 beats are used to complete one complete cycle, and the total stroke length is set by 2 complete cycles.

[0023] Figure 6 This is a schematic diagram of Embodiment 1, in which the armature is pushed out a distance f by the electromagnetic thrust after the coil group A+ is energized.

[0024] Figure 7 This is a schematic diagram of Embodiment 1, in which after the coil group B+ is energized, the armature is pushed out a distance of 2 f by the electromagnetic thrust.

[0025] Figure 8 This is a schematic diagram of Embodiment 1, in which after the coil group A is energized, the armature is pushed out a distance of 3 f by the electromagnetic thrust.

[0026] Fig. 9 This is a schematic diagram of Embodiment 1, in which after the coil group B is energized, the armature is pushed out of a distance of 4 f by the electromagnetic thrust.

[0027] Fig.10 This is a schematic diagram of embodiment 1, in which the armature is pushed out 8 f distances by the electromagnetic thrust after completing 2 complete beat cycles.

[0028] Fig.11 This is a driving control circuit diagram of Embodiment 1, in which 8 beats are used to complete one complete cycle, and the total stroke length is set by two complete cycles.

[0029] Fig.12 It is a partial structure and control circuit diagram of the position sensing strip of the second embodiment.

[0030] Fig.13 It is a partial structure and control circuit diagram of the position sensing strip of the third embodiment.

[0031] Fig.14 It is a structural diagram of embodiment 4.

[0032] Fig.15 It is a schematic diagram of the locked state of the armature terminal stroke position in the fourth embodiment.

[0033] The symbols in the figure are: 1 is the electromagnet frame; 2 is the armature; 3 is the restoring spring, 4 is the armature permanent magnet group, 5 is the coil group, 6 is the control circuit; 6 is the beat signal generator, 7 is the beat signal distributor, 8 is the drive module, 6-1 and 6-2 are the armature position sensing strips, 6-1-0 is the first permanent magnet, 6-2-0 is the second permanent magnet, 6-1-1 is the first Hall switch; 6-2-1 is the second Hall switch, 901 is the stroke terminal locking coil, 902 is the stroke terminal locking yoke, 903 is the stroke terminal locking armature, and f is the axial dimension of a coil. DETAILED DESCRIPTION

[0034] The following is a further detailed description of the specific implementation of the present invention in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the practical application of the present invention, but are not intended to limit the scope of the present invention.

[0035] Embodiment 1:

[0036] This embodiment provides Figure 4 The main structure of a long-stroke electromagnet shown includes: an electromagnet frame 1, an armature 2, a restoring spring 3, a permanent magnet group 4 and a coil group 5.

[0037] The permanent magnet group 4 is composed of two axial end faces of the magnetic poles, each of which has an arrangement of single permanent magnets with opposite magnetic poles on adjacent end faces. The axial length of a single permanent magnet is equal to the sum of the thicknesses of the two coils.

[0038] The eight coils are divided into two groups of coils, A and B, and the individual coils of the two groups of coils are arranged interlaced with each other. The coil groups are sleeved on the outer periphery of the permanent magnet group 4.

[0039] The control circuit of this embodiment is shown in FIG. Figure 5The beat signal generator 6 is composed of IC1 time base chip NE555 and peripheral components; the beat signal distributor 7 is realized by IC2 and IC3 two decimal counting chips CD4017 and peripheral components; the driving module 8 is composed of IC3 and IC4 full-bridge driving chips RZ7886 and peripheral components, and the four output terminals of RZ7886 are respectively connected to the four ends of the two groups of coils A and B.

[0040] The OUT terminal of IC1 is connected to the counting input terminal CP of the counting circuit IC2 through a resistor. IC2 will count along with the beat signal output by IC1, and the four output terminals of IC2 will form high and low level changes to complete the distribution of the beat signal. The distributed beat signal is sent to the four control terminals of the two full-bridge driver chips RZ7886, IC4 and IC5, respectively, to control the on, off and direction of the current of group A coil and group B coil.

[0041] The multiple output terminals of IC3 are connected to the counting input terminal of IC2 through a multi-gear selection switch k and a diode D. Its function is to set the number of times the beat signal needs to complete a complete cycle according to the terminal stroke length of the electromagnet. The switch K of this embodiment is in a setting position corresponding to 2 complete cycles of the terminal stroke of the electromagnet.

[0042] By adjusting the potentiometer W in the beat signal generator, the cycle of the beat signal change can be changed, that is, the speed of the power on and off and current switching beat of the coils of group A and group B can be changed, thereby controlling the speed of the armature extension. Because the movement of the armature has a certain inertia, the change of the beat cannot be adjusted too fast.

[0043] The currents of coil group A and coil group B are connected, disconnected and reversed in a rhythmic manner, generating electromagnetic thrust of a certain direction on the permanent magnet. The electromagnetic thrust generated by the coil current in each rhythmic period and the corresponding distance of the armature being pushed out are as follows:

[0044] See Figure 6 , when only the A group coil is powered in the positive direction (marked as A+), the current direction is A1 to A2, and the magnetic field generated by the current of the four coils in the A group generates an electromagnetic thrust from right to left on the corresponding permanent magnet, and the armature is pushed from the initial position from right to left by a distance corresponding to one beat and one coil thickness - f. At this time, the electromagnetic thrust and the elastic force of the spring are balanced;

[0045] See Figure 7, while the power of group A coil is turned off, the positive power (marked as B+) is supplied to group B coil, and the current direction is from B1 to B2. The magnetic field generated by the current of the four coils of group B generates an electromagnetic thrust from right to left on the corresponding permanent magnet again, and the armature is pushed to the left again by a distance corresponding to one beat and one coil thickness - f. At this time, the armature is pushed out 2f from the initial position, and the electromagnetic thrust and the elastic force of the spring reach a new balance;

[0046] See Figure 8 , when the power of the coil of group B is cut off, the reverse power is supplied to the coil of group A (marked as A-). When the current direction is from A2 to A1, the magnetic field generated by the current of the four coils of group A generates an electromagnetic thrust from right to left on the corresponding permanent magnet again, and the armature is pushed to the left again by a distance corresponding to one beat and one coil thickness - f. At this time, the armature is pushed out 3f from the initial position, and the electromagnetic thrust and the elastic force of the spring reach a new balance;

[0047] See Fig. 9 , when the power of coil group A is turned off, reverse power is supplied to coil group B (marked as B-). When the current direction is from B2 to B1, the magnetic field generated by the current of the four coils of group B generates an electromagnetic thrust from right to left on the corresponding permanent magnets again, and the armature is pushed to the left by another coil thickness - f. At this time, the armature is pushed out 4f from the initial position, and the electromagnetic thrust and the elastic force of the spring reach a new balance;

[0048] like Fig.10 Repeat the above steps. The current of the coil group is turned on, off and reversed according to the beat. After 8 beats, the distance pushed to the left by the armature from the initial position reaches 8 coil thicknesses - 8f. The armature is pushed to the end of the stroke. The counting CP terminal of IC2 is clamped by the high level output by the 02 terminal of IC3 and cannot jump. IC2 stops counting, that is, the current on and off and direction switching of the coil of group A or group B are stopped. The current on and off state of the coil of group A or group B remains unchanged, and the armature is locked at the end of the stroke by the unchanged electromagnetic force.

[0049] If the length of the armature is made longer, the number of complete cycles is set to a larger value, and the above steps are repeated continuously, the final ejection stroke of the armature will also increase accordingly.

[0050] When the electromagnet needs to be released, the control circuit power is disconnected, the A or B coil is de-energized, the electromagnetic thrust disappears, and the armature moves back to the initial position to the right under the action of the restoring spring.

[0051] If adopted Fig.11In the control circuit, the power-on pattern of the two groups of coils A and B becomes A+, A+B+, B+, B+A-, A-, AB-, B-, B-A+..., forming a complete cycle that requires 8 beats to complete. Each beat produces a pushing distance of 1 / 2f on the armature and permanent magnet group. The current of the coil group needs to change in 8 beats to push the armature out a distance of 4f. The armature is pushed out of the full travel distance of 8f in 16 beats, which means that two complete beat cycles need to be completed.

[0052] Embodiment 2:

[0053] This embodiment further discloses on the basis of the first embodiment:

[0054] The control circuit of this embodiment is as follows Fig.12 As shown;

[0055] The present embodiment is different from the first embodiment in that the beat signal generator does not use IC1, but is instead composed of a first position sensing strip 6-1 and a first Hall switch 6-1-1. A plurality of first permanent magnets 6-1-0 are sequentially arranged and fixed on the first position sensing strip 6-1. The arrangement distance between each first permanent magnet 6-1-0 is the axial length of one coil - f. The length of the first position sensing strip 6-1 is similar to that of the armature 2, and is rigidly connected to the tail of the armature 2. The first Hall switch 6-1-1 is fixedly mounted on the electromagnet frame 1.

[0056] When the first position sensing strip 6-1 changes position following the push-out of the armature 2, the first permanent magnet 6-1-0 on the first position sensing strip 6-1 will cause the first Hall switch 6-1-1 that is close to it to output a high-level signal. When the first permanent magnets 6-1-0 arranged on the first position sensing strip 6-1 are close to the first Hall switch 6-1-1 in sequence, the first Hall switch 6-1-1 will output beat signals to the beat signal distributor in sequence. The beat signal distributor sends the distributed beat signals to each control end of the driving module, thereby controlling the voltage and direction change of each output end of the driving module, and further controlling the on / off and direction change of the current in the coil group 5, and finally generating an electromagnetic force with a determined direction to push the armature 2 to move.

[0057] Embodiment three:

[0058] This embodiment further discloses on the basis of the first embodiment:

[0059] The control circuit of this embodiment is as follows Fig.12 As shown;

[0060] The present embodiment is different from the first embodiment in that the beat signal generator 6 does not use IC1, and the beat distributor 7 does not use IC2 and IC3, and the beat signal generation and distribution functions are instead completed by a second position sensing strip 6-2 and four second Hall switches 6-2-1.

[0061] A plurality of second permanent magnets 6-2-0 are fixedly arranged in sequence on the second position sensing strip 6-2, and the arrangement distance between each second permanent magnet 6-2-0 is equal to the sum of the axial lengths of the four coils - 4f. The length of the second position sensing strip 6-2 is similar to the length of the armature 2, and is rigidly connected to the tail of the armature 2. Four second Hall switches 6-2-1 are fixedly mounted on the electromagnet frame 1.

[0062] When the second position sensing strip 6-2 changes position following the push of the armature 2, the second permanent magnet 6-2-0 on the second position sensing strip 6-2 will cause the adjacent second Hall switch 6-2-1 to output a high level signal. When the second permanent magnet 6-2-0 of the second position sensing strip 6-2 approaches the four second Hall switches 6-2-1 in sequence, the four second Hall switches 6-2-1 distribute the beat signal in sequence to the four control terminals of the driving module 8, thereby controlling the voltage and direction change of each output terminal of the driving module 8, and further controlling the on / off and direction change of the current in the coil group 5, and finally generating an electromagnetic force with a determined direction to push the armature 2 to move.

[0063] The advantages of the second and third embodiments are that the ejection speed of the armature is only determined by the inertia of the armature itself and the magnitude of the electromagnetic thrust. The disadvantage is that compared with the first embodiment, the structure is more complicated.

[0064] Embodiment 4:

[0065] This embodiment further discloses on the basis of the first embodiment:

[0066] like Fig.15 As shown, this embodiment is different from the first embodiment in that it also includes an armature terminal travel locking device, and the armature terminal travel locking device includes a locking coil 901, a yoke 902, and a locking armature 903. The locking coil 901 is wound around the rear half of the armature 2, and the yoke 902 is arranged on the periphery of the locking coil 901. The locking armature 903 is arranged at the tail end of the armature 2.

[0067] When the armature 2 is pushed out to the end of its stroke, the locking coil 901 is energized to generate a locking magnetic field, and the magnetic lines of force generated by the yoke 902 and the locking armature 903 for the coil group 5 form a closed magnetic circuit, forming a locking force for the armature 2. This locking force is superimposed on the thrust exerted on the permanent magnet of the armature 2, thereby greatly enhancing the locking effect of the armature 2 at the end of its stroke.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principle of the present invention. These improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. An ultra-long stroke electromagnet structure, characterized in that: include: An electromagnet frame (1), an armature (2), a restoring spring (3), a permanent magnet group (4), a coil group (5), a beat signal generator (6), a beat signal distributor (7) and a drive module (8), wherein the permanent magnet group (4) is composed of two end faces of its magnetic poles in the axial direction, and each single permanent magnet is arranged with the magnetic poles of each adjacent end face opposite to each other; the permanent magnet group (4) is axially distributed on the armature (2); the coil group (5) is composed of two groups of coils arranged in a manner of interlacing with each other and sleeved on the outer periphery of the permanent magnet group (4); the beat signal generator (6), the beat signal distributor (7) and the drive module (8) are connected to a DC power supply and the coil group (5). ), the pulse output end of the beat signal generator (6) is connected to the input end of the beat signal distributor (7), the four output ends of the beat signal distributor (7) are respectively connected to the four control input ends of the drive module (8), the four output ends of the drive module (8) are respectively connected to the four ends of the coil group (5), the drive module (8) controls the on / off and direction change of the two coil currents of the coil group (5) according to the high and low level changes of the output end of the beat signal distributor (7), the current of the coil group (5) generates an electromagnetic force with a certain direction on the permanent magnet group (4), pushes the permanent magnet group (4) and drives the armature (2) to extend and move.

2. The ultra-long stroke electromagnet structure according to claim 1, characterized in that: The beat signal generator (6) and the beat signal distributor (7) are composed of pure electronic circuits, or are composed of a position sensing strip that moves synchronously with the armature (2) and a Hall switch fixedly mounted on the electromagnet frame.

3. The ultra-long stroke electromagnet structure according to claim 2, characterized in that: The core component of the signal generator (6) composed of electronic circuits is the time base chip NE555.

4. The ultra-long stroke electromagnet structure according to claim 2, characterized in that: The core component of the beat signal distributor (7) is a decimal counting chip CD4017.

5. The ultra-long stroke electromagnet structure according to claim 3, characterized in that: The signal generator (6) formed by the electronic circuit changes the cycle of the beat signal, thereby changing the speed of the beat of the current on and off or the change of direction of the coil group (5), thereby adjusting the speed of the armature pushing out.

6. The ultra-long stroke electromagnet structure according to claim 2, characterized in that: The beat signal generator (6) is composed of a first position sensing strip (6-1) and a first Hall switch (6-1-1). The length of the first position sensing strip (6-1) is similar to that of the armature (2). A plurality of separated first permanent magnets (6-1-0) are distributed on the first position sensing strip. The spacing between the first permanent magnets (6-1-0) is the same as the axial dimension of a coil. The first position sensing strip (6-1) is rigidly connected to the tail end of the armature (2). The first Hall switch (6-1-1) is fixedly mounted on the electromagnet frame (1). The output end of the first Hall switch (6-1-1) is connected to the beat signal distributor (7). ), each first permanent magnet (6-1-0) on the first position sensing strip (6-1) can form proximity sensing for the first Hall switch (6-1-1), and when a first permanent magnet (6-1-0) on the first position sensing strip (6-1) is close to the first Hall switch (6-1-1), the first Hall switch (6-1-1) outputs a high level to the signal input end of the beat signal distributor (7), so that each output state of the beat signal distributor (7) changes, thereby causing the control input end state of the driving module (8) to change, and finally causing the on / off and direction of the current of the coil group (5) to change.

7. The ultra-long stroke electromagnet structure according to claim 2, characterized in that: The beat signal generator (6) and the beat distributor (7) are composed of a second position sensing strip (6-2) and four second Hall switches (6-2-1). The second position sensing strip (6-2) is provided with a plurality of separated second permanent magnets (6-2-0) distributed in the axial direction. The spacing between the second permanent magnets (6-2-0) is equal to the sum of the axial dimensions of the four coils. The length of the second position sensing strip (6-2) is similar to the length of the armature (2) and is rigidly connected to the tail end of the armature (2). The four second Hall switches (6-2-1) are fixedly mounted on the electromagnet frame. (1), the spacing between the four second Hall switches (6-2-1) is the same as the axial dimension of one coil, the four output ends of the four second Hall switches (6-2-1) are respectively connected to the four control input ends of the driving module (8), when a second permanent magnet (6-2-0) on the second position sensing strip (6-2) approaches the four second Hall switches (6-2-1) in sequence, it will output high levels to the four control ends of the driving module (8) in sequence, completing the distribution function of the beat signal according to the actual push-out position of the armature, and finally causing the current of the coil group (5) to be turned on, off and changed in direction.

8. The ultra-long stroke electromagnet structure according to claim 2, characterized in that: The core component of the driving module (8) is a full-bridge driving chip RZ7886.

9. The ultra-long stroke electromagnet structure according to claim 1, characterized in that: The permanent magnet group (4) on the armature is composed of separate permanent magnets arranged one by one, or a high coercive force magnetic material rod is magnetized in sections to form a permanent magnet armature.

10. An ultra-long stroke electromagnet structure according to any one of claims 1 to 9, characterized in that: It also includes an armature terminal travel locking device (9), the armature terminal travel locking device (9) including a locking coil (901), a yoke (902), and a locking armature (903), the locking coil (901) being installed at the rear end of the coil group (5), the yoke (902) being arranged on the periphery of the locking coil (901), and the locking armature (903) being arranged at the rear end of the armature (2).

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