JP2003068522A - Linear actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear actuator which enables the stroke enlargement, the thrust increase, and the hysteresis lessening while keeping horizontal suction force properties. SOLUTION: In this linear actuator consisting of a needle and a stator, a pair of cylindrical rings (4) are counterposed to each other on the same axis with a certain vacant space from the peripheral face of the needle, and a pair of pole pieces (2) are arranged on the same axis on the side of both end faces of the needle with a certain vacant space from the peripheral face of the needle. Each of the permanent magnets (3) in a pair is interposed in each axial vacant space each made between each cylindrical ring and each pole piece. A drive coil (7) is wound on each peripheral face of the cylindrical rings in a pair, the pole pieces in a pair, and the permanent magnets in a pair. The permanent magnets in a pair are magnetized reversely in axial direction to each other. The peripheral face of each inner end of the pole piece in a pair is in shape of a taper having a thickness and an angle determined in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a movable iron core type electromagnetic linear actuator useful as a positioning device for electrohydraulic control equipment, FA equipment, machine tools and the like.

[0002]

2. Description of the Related Art Conventionally, a voice coil type linear motor has been widely used as an electromagnetic linear actuator for relatively light load applications, but as an electromechanical conversion mechanism for an electrohydraulic proportional control device or an electrohydraulic servo control device. Alternatively, a large thrust force is required for an electromagnetic linear actuator used as a drive mechanism for a positioning device such as FA equipment and machine tools. In order to meet such demands, an electromagnetic linear actuator that has a relatively small size and generates a large thrust by incorporating a rare earth permanent magnet having a large coercive force into an electromagnetic plunger including a fixed iron core having a solenoid coil and a movable iron core has been conventionally known. ing.

For example, in Japanese Patent Laid-Open No. 7-303363, a plurality of cylindrical permanent magnets magnetized in the radial direction are alternately magnetized in the outer circumference of a cylindrical movable yoke (movable iron core) in order to obtain a large thrust. On the inner periphery of the cylindrical fixed yoke (fixed iron core), a plurality of drive coils corresponding to the permanent magnets of the movable yoke are arranged in the axial direction. A movable magnetic linear actuator having a plurality of magnetic poles divided into two is described.

Although a large thrust is certainly obtained in the above prior art, a large number of cylindrical permanent magnets and drive coils are required to obtain this large thrust, the structure is complicated, and a large number of magnetic circuits are present. It will be. Therefore, the magnetic circuit may become non-uniform, and this non-uniformity (variation) may cause an increase in thrust hysteresis.

"Hydraulic pressure and air pressure" (Vol. 27, No. 4)
No. 14, pp. 16-16, published in July 1996, Japan Hydro-Pneumatic Society) describes an electro-hydraulic servo valve that uses a linear motor for its drive unit.
As shown in FIG. 3, the left and right yokes (fixed iron cores) 32a and 32b are arranged so as to form a gap on each side of the plunger (movable iron core) 31, and the inner circumference of each yoke is located on both sides of the plunger 31. So that the cylindrical permanent magnet 3
3a and 33b are fixedly arranged, respectively, and a pair of drive coils 34a and 34b are arranged on the outside thereof to form the case 3
5 is a movable iron core type electromagnetic linear actuator having a structure in which the plunger 31 is supported on both sides by a pair of leaf springs 36a and 36b fixed to the ends of the yokes 32a and 32b.

In the above linear actuator, the magnetization directions of the permanent magnets 33a and 33b on both sides are the plunger 31.
Are opposite to each other with respect to the axial direction, for example, the N poles face the outer leaf springs, and the S poles face each other with a space in between. The pair of coils 34a and 34b are excited by a direct current to generate magnetic flux in the same direction. Since the magnetization directions of the permanent magnets 33a and 33b are opposite to each other, the magnetic flux in the same direction generated by the excitation of the coil and the magnetic flux of the permanent magnet increase on one side and decrease on the other side, resulting in a difference in magnetic flux. The plunger moves left and right.

However, in the above-mentioned prior art, the thrust characteristic is equivalent to that of a general plunger type electromagnet (see FIG. 4), and the horizontal attractive force characteristic (the attractive force, that is, the thrust force is substantially constant with respect to the stroke change of the movable iron core). Characteristics) that cannot be secured,
The effective stroke of the movable core was extremely small and limited, and it was difficult to increase the stroke. The stroke here means the amount of movement of a mover such as a plunger (the same applies hereinafter).

[0008]

SUMMARY OF THE INVENTION In view of such a situation, the present invention enables a large stroke, a large thrust, and a small hysteresis while maintaining the horizontal suction force characteristic, and is bidirectionally movable with a simple structure. The present invention is intended to provide a linear actuator having properties. In other words, a linear actuator that realizes a small hysteresis by minimizing the number of permanent magnets and drive coils to suppress the complication of the magnetic circuit, and that can achieve a large stroke and a large thrust while maintaining the horizontal attraction characteristics. It is an object of the invention to provide.

[0009]

According to a first aspect of the present invention, in a linear actuator, the linear actuator comprises a mover and a stator, the stator being at least a pair of cylindrical rings, a pair of magnetic pole pieces, and a pair of magnetic pole pieces. A permanent magnet and a linear actuator composed of a single or a plurality of drive coils, wherein the pair of cylindrical rings are coaxially face-to-face arranged with the outer peripheral surface of the mover with a certain gap. The pair of magnetic pole pieces are coaxially arranged on both end surface sides of the mover with a certain gap from the outer peripheral surface of the mover, and are formed between the cylindrical rings and the magnetic pole pieces, respectively. Each of the pair of permanent magnets is interposed in each axial gap, and at least over a range that at least partially covers the pair of cylindrical rings, the pair of magnetic pole pieces, and the outer peripheral surfaces of the pair of permanent magnets. One drive coil The pair of permanent magnets are magnetized in opposite directions in the axial direction, and the outer peripheral surfaces of the inner end portions of the pair of magnetic pole pieces have a tapered shape having a predetermined thickness and angle. Is characterized by.

According to the invention of claim 2, claim 1
In the linear actuator according to the item (1), the axially opposite end surfaces of the mover are positioned within the axial length of the tapered shape in the axial gaps formed between the pair of magnetic pole pieces, respectively. It is characterized by doing.

Means for solving the above problems will be described in detail below.

FIG. 2 is an explanatory diagram showing the basic structure of the present invention. As shown in FIG. 2, the present invention comprises a pair of cylindrical rings 4, a pair of cylindrical permanent magnets 3, a pair of magnetic pole pieces 2, a drive coil 7, a bobbin 6 for storing the drive coil, and a case 5. The stator and the plunger 8, which is a mover, form a pair of symmetrical magnetic circuits. The outer peripheral surface of the inner end portion of the pole piece 2 has a conical taper shape. Cylindrical air gaps are provided between both ends of the plunger 8 in the axial direction and the pair of magnetic pole pieces 2, and the plunger 8 is positioned within and in the vicinity of the axial length of the tapered portion of the magnetic pole piece 2 in the air gap. It is movable in the axial direction. The pair of cylindrical permanent magnets 3 are magnetized in advance in mutually opposite axial directions.

When the plunger 8 is in the neutral position (however, the coil applied current is 0), the left and right magnetic circuits are completely symmetrical, and the magnitude of the magnetic flux generated by each permanent magnet 3 (φ in FIG. 2). _m and -φ _m ) are equal and opposite, the attraction forces at the left and right ends of the plunger 8 are balanced and no thrust force is exerted on the plunger 8. Next, when a current is applied to the drive coil 7, a magnetic flux (represented by φ _i in FIG. 2) due to this causes a summing or differential magnetic flux in the left and right magnetic circuits, that is, φ _i + φ _m and φ _i −. φ _m is generated, the suction force at both ends of the plunger 8 becomes unbalanced, and the plunger 8
Thrust is generated. A large change in magnetic flux can be obtained due to the feature that magnetic flux is applied to the magnetic flux of the permanent magnet by addition and subtraction of the permanent magnet simultaneously due to the coil applied current. If the demagnetization of the permanent magnet is not taken into consideration, the magnetic flux due to the applied current can be applied up to a value where φ _i and φ _m are equivalent, and a large thrust can be obtained with a small size and a small input power.

Further, as described above, the outer peripheral surface of the inner end portion of the magnetic pole piece 2 is tapered, and the saturation and leakage of magnetic flux are regulated by setting the tapered shape to an appropriate angle and thickness. The suction force with respect to the stroke change of the plunger 8 is kept substantially constant within and near the axial length of the taper portion.

Further, the plunger 8 is arranged within the axial length of the taper portion of the magnetic pole piece 2 in the axial gap formed between the plunger 8 and the magnetic pole piece 2. Therefore, the horizontal attraction force characteristic with respect to the stroke change of the plunger 8 in both the left and right directions can be well secured.

In addition, since the parts structure is simple and the magnetic circuit is simple, it is obvious that the variation of the magnetic circuit is reduced and a small hysteresis can be realized.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the parts denoted by the same reference numerals as those in the drawings represent the same or equivalent objects.

FIG. 1 shows an example of an embodiment of the present invention.
A pair of cylindrical rings 4, a pair of cylindrical permanent magnets 3, a pair of magnetic pole pieces 2, a drive coil 7, a stator formed of a bobbin 6 for housing the drive coil, and a case 5 and a plunger 8 form a pair of symmetrical magnetic fields. The pair of cylindrical permanent magnets 3 are arranged so that a circuit can be formed, and the pair of cylindrical permanent magnets 3 are magnetized in the axial direction, and their magnetization directions are opposite to each other. The permanent magnets 3 are arranged so as to face each other). Further, the pair of cylindrical rings 4 are assembled so as to be in contact with each other, and the present actuator is configured to be bilaterally symmetrical with respect to the contact surface in the axial direction. The outer peripheral surface of the inner end portion of the magnetic pole piece 2 has a conical taper shape, and the inner peripheral surface of the magnetic pole piece 2 has a cylindrical void in the axial direction, and the plunger 8 can move in the axial direction in this void. Becomes A plunger pin 1 is inserted into the plunger 8, and the plunger pin 1 is supported by a bearing 10 and the plunger 8 moves left and right while maintaining an appropriate gap with the inner peripheral surface. When the end of the plunger 8 moves, a collar 9 made of a non-magnetic material is inserted in the end face of the pole piece 2 in order to prevent the collar 8 from being attracted to the pole piece 2 (in the present embodiment, the collar 9). The plate thickness of 9 was 1.5 mm). Further, the plunger 8 is configured to be positioned within the range of the axial length of the tapered portion of the magnetic pole piece 2 in the neutral position. When a current is applied to the drive coil 7 of the actuator configured as described above, the magnetic flux causes a summing or differential magnetic flux in the left and right magnetic circuits, and the attraction force at both ends of the plunger 8 becomes unbalanced. A thrust force is generated on the plunger 8 and the plunger 8 is movable in both left and right directions.

The components of the present invention include a plunger pin 1
Is stainless steel, magnetic pole piece 2, cylindrical ring 4 and plunger 8 are free-cutting pure iron, permanent magnet 3 is Nd-Fe-B system sintered magnet, case 5 is carbon steel pipe for machine structure, drive coil 7
Is a polyester steel wire, and the collar 9 is a copper alloy. An Fe-BR type sintered magnet or the like may be used as the permanent magnet. The bearing 10 is a linear ball bearing.

In this embodiment, a single coil is used as an example, but a plurality of divided coils may be used for the purpose of improving responsiveness and reducing inductance. The linear actuator of the present invention is not limited to the illustrated examples and material examples described above, and it goes without saying that various modifications can be made without departing from the scope of the present invention.

[0021]

As described above, the first aspect of the present invention is as described above.
According to the linear actuators described in (1) to (2), it is possible to obtain an excellent effect that it is possible to increase the stroke, increase the thrust, and decrease the hysteresis while maintaining the horizontal suction force characteristic. Tests have confirmed that the thrust hysteresis can be reduced to about 1/10 of that of the conventional technique. Moreover, since a simple structure can be realized, handling and maintenance are easy, which contributes to cost reduction.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing the configuration of an embodiment of the present invention.

FIG. 2 is a basic configuration diagram for explaining the operation of the present invention.

FIG. 3 is a schematic configuration diagram for explaining an example of a conventional technique.

FIG. 4 is a schematic configuration diagram for explaining an example of a conventional technique.

[Explanation of symbols]

1: Plunger pin 2: Magnetic pole piece 3: Permanent magnet 4: Cylindrical ring 5: Case 6: Bobbin 7: Drive coil 8: Plunger 9: Color 10: Bearing 31: Plunger 32a, 32b: Yoke 33a, 33b: Permanent magnets 34a, 34b: drive coil 35: Case 36a, 36b: leaf spring

Claims (2)

[Claims] 1. A linear actuator comprising a mover and a stator, the stator including at least a pair of cylindrical rings, a pair of magnetic pole pieces, a pair of permanent magnets, and a single or a plurality of drive coils. The pair of cylindrical rings are coaxially face-to-face arranged with the outer peripheral surface of the mover provided with a constant gap, and the pair of magnetic pole pieces provide a constant gap with the outer peripheral surface of the mover. Each of the pair of permanent magnets is disposed coaxially on both ends of the mover, and each of the pair of permanent magnets is interposed in each axial gap formed between each of the cylindrical rings and each of the magnetic pole pieces. Of the cylindrical ring, the pair of magnetic pole pieces, and at least one drive coil is wound around a range that at least partially covers the outer peripheral surfaces of the pair of permanent magnets. Magnetized in the opposite direction in the axial direction, Linear actuator which is a tapered shape having a thickness and angle of the outer peripheral surface is predetermined for each inner ends of a pair of pole pieces. 2. The axially opposite end faces of the mover are located within the axial length of the tapered shape in the axial gaps formed between the pair of magnetic pole pieces, respectively. The linear actuator according to claim 1, wherein: