JP2024075187A - Bidirectional Actuator - Google Patents

Abstract

[Problem] To provide a bidirectional actuator that can absorb external forces and return a shaft to its original position even when it receives a large external force such as vibration with a small displacement when it is not energized. [Solution] The actuator 100 according to the present invention is characterized by comprising a cylindrically wound coil 106, a fixed core 108 that covers the coil, a movable core 110 that moves in both directions in the axial direction of the coil inside the fixed core, a pair of magnets 120a, 120b that hold the movable core at stroke ends 128a, 128b on both sides, a shaft 102 that slidably passes through the inside of the movable core, a pair of holding members 122a, 122b that are provided on the shaft and protrude from both sides of the movable core at a predetermined distance and are capable of abutting against the fixed core, and a pair of elastic bodies 112a, 112b that are respectively arranged between the pair of holding members and both sides of the movable core. [Selected Figure] Figure 1

Description

The present invention relates to a bidirectional actuator that can actively move a shaft in both directions.

As an example, in a bidirectional actuator using a coil and a movable core, when the coil is excited, the movable core is attracted and can move (e.g., Patent Documents 1 and 2).

Patent document 1 describes a linear actuator in which a movable core moves in both directions when electricity is applied to a coil. This linear actuator includes a movable core, a pair of fixed cores, a pair of permanent magnets whose magnetic poles face the fixed core, and a pair of non-magnetic members. Patent document 1 describes how a pair of non-magnetic members is disposed between the movable core and the pair of fixed cores, thereby preventing the movable core from being attracted to the fixed cores as the movable core moves.

Patent document 2 describes an actuator that includes a movable core that has a permanent magnet and is integrated with a shaft, two fixed cores, two electric coils, and two elastic members. This actuator has two fixed cores, each equipped with an electric coil, disposed on either side of the movable core that has a permanent magnet.

In the actuator, the magnetic flux generated by the permanent magnet holds the movable core in two stable positions when no current is applied, and the movable core is moved from one stable position to the other by applying current to each of the two electric coils. The two elastic members are also disposed between the movable core and the fixed core, and are compressed between them at the stroke end of the movable core when no current is applied.

JP 2003-68522 A JP 2012-511823 A

The linear actuator of Patent Document 1 has a non-magnetic member interposed between the movable iron core and the fixed iron core to form a gap, which prevents the movable iron core from coming into close contact with the fixed iron core, thereby increasing the force of attraction (thrust) when the movable iron core separates from the fixed iron core when current is applied. However, because a gap is formed between the movable iron core and the fixed iron core, the force of the magnetic flux of the permanent magnet that holds the movable iron core when current is not applied is reduced.

In the actuator of Patent Document 2, an elastic member is disposed between the movable iron core and the fixed iron core, so that when the movable iron core separates from the fixed iron core while current is flowing, the elastic body that was compressed while current was not flowing expands, allowing the movable iron core to separate and assist the suction force.

However, in the actuator of Patent Document 2, the elastic body is compressed when not energized and holds the movable core in two stable positions, so the force with which the movable core adheres to the fixed core is weakened by the elastic force of the elastic body, reducing the force with which the movable core is held. For this reason, if an external force such as vibration (an external force with a small amount of displacement and a large force) is applied when not energized, the movable core may separate from the fixed core, and the shaft, which is integrated with the movable core, may not be able to return to a stable position.

In view of these problems, the present invention aims to provide a bidirectional actuator that can absorb external forces and return the shaft to its original position even when it receives a large external force such as vibration with a small displacement when not energized.

To solve the above problems, a typical configuration of a bidirectional actuator according to the present invention is characterized by comprising a cylindrically wound coil, a fixed core covering the coil, a movable core that moves in both directions inside the fixed core in the axial direction of the coil, a pair of magnets that hold the movable core at both stroke ends, a shaft that slidably passes through the inside of the movable core, a pair of holding members that are provided on the shaft and protrude from both sides of the movable core at a predetermined distance and can abut against the fixed core, and a pair of elastic bodies that are respectively arranged between the pair of holding members and both sides of the movable core.

With the above configuration, even if an external force such as vibration (an external force with a small amount of displacement but a large force) is applied when the current is not applied, the external force can be absorbed and the shaft can be returned to its original position. Therefore, the attractive force of the magnet can be small, which allows for the magnet to be made smaller and less expensive.

In addition, when current is applied, there is no need to move the shaft to start the moving core (there is no need to overcome the opposing load), so the moving core can be moved by the weak magnetomotive force of the coil. Furthermore, once the moving core starts moving, the magnetic flux of the magnet that tries to attract the moving core and fixed core weakens rapidly, so when the shaft is moved (overcoming the opposing load), the magnetic flux of the magnet that tries to pass in the opposite direction to the attraction direction is greatly reduced. Therefore, the magnetomotive force of the coil can be small, which allows for the coil to be made smaller and less expensive.

The present invention provides a bidirectional actuator that can absorb external forces and return the shaft to its original position even when it receives a large external force such as vibration with a small displacement when not energized.

1 is an overall configuration diagram of a bidirectional actuator according to an embodiment of the present invention; 2 is a diagram illustrating a state when no current is applied to the actuator of FIG. 1. FIG. 2 is a diagram illustrating a state when a current is applied to the actuator of FIG. 1. FIG. 2 is a graph showing the characteristics of the actuator of FIG. 1 .

The preferred embodiment of the present invention will be described in detail below with reference to the attached drawings. The dimensions, materials, and other specific values shown in the embodiment are merely examples to facilitate understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements that have substantially the same function and configuration are given the same reference numerals to avoid duplicated explanations, and elements that are not directly related to the present invention are not illustrated.

Figure 1 is a diagram showing the overall configuration of a bidirectional actuator (hereinafter, actuator 100) according to an embodiment of the present invention. The actuator 100 is a device that includes a shaft 102 to which a specific member (counter load) is fixed, and is capable of actively moving the shaft 102 in both directions.

In addition to the shaft 102, the actuator 100 includes a coil 106 and a fixed core 108. The fixed core 108 includes a casing 104 and side plates 126a, 126b, which may be configured as separate components, and if they are separate components, the division between them may be changed as appropriate, or they may be integrated. In this way, the fixed core 108 including the casing 104 and side plates 126a, 126b covers the coil 106 as a whole, as shown in the figure. The coil 106 is disposed inside the casing 104 of the fixed core 108 and is wound cylindrically. The fixed core 108 is also made of a magnetic material and forms a magnetic circuit.

The fixed core 108 has a circumferential slit 114 formed on its inner peripheral surface. The slit 114 is defined by an end face 116a on one side (left side in the figure) of the fixed core 108 and an end face 116b on the other side (right side in the figure) that face each other.

The actuator 100 further comprises a movable iron core 110 and a pair of elastic bodies 112a, 112b. The movable iron core 110 moves in both directions in the axial direction of the coil 106 inside the fixed iron core 108. The movable iron core 110 has a movable yoke 118 and a pair of magnets 120a, 120b. The movable yoke 118 protrudes in the radial direction and is disposed between the slits 114. The pair of magnets 120a, 120b are permanent magnets, and their magnetic poles face the movable yoke 118.

The shaft 102 slidably passes through the inside of the movable core 110. Therefore, the shaft 102 does not move together with the movable core 110. The shaft 102 also has a pair of retaining members 122a, 122b. The pair of retaining members 122a, 122b protrude radially from both sides of the movable core 110, i.e., one end 124a and the other end 124b, at a predetermined distance, and face the side plates 126a, 126b of the fixed core 108, and are arranged in positions where they can abut against the side plates 126a, 126b.

The pair of elastic bodies 112a, 112b are compression coil springs, and are respectively disposed between the pair of holding members 122a, 122b and one end 124a and the other end 124b of the movable core 110. In this way, the movable core 110 is supported on the shaft 102 via the pair of elastic bodies 112a, 112b.

The movable core 110 also has stroke ends 128a, 128b on both sides formed on the movable yoke 118. The stroke ends 128a, 128b face one end surface 116a and the other end surface 116b, respectively, which define the slit 114 of the fixed core 108.

The characteristics and operation of the actuator 100 in FIG. 1 will be described below. FIG. 2 is a diagram illustrating the state of the actuator 100 in FIG. 1 when not energized. Note that the values shown below are merely examples and are not limiting. When not energized, the movable iron core 110 has one stroke end 128a attracted to one end surface 116a of the fixed iron core 108 by an attractive holding force Fa (e.g., 100 N) due to the magnetic flux Ra of the pair of magnets 120a, 120b shown in FIG. 2(a).

At this time, the retaining member 122a on one side abuts against the horizontal plate 126a of the casing 104, and the elastic body 112a on one side is in a compressed state. In the pair of elastic bodies 112a, 112b, the elastic body 112a on one side is compressed and the elastic body 112b on the other side is expanded, generating a difference in the elastic forces of the elastic bodies 112a, 112b on one side and the other side, that is, a spring resultant force Fb (e.g., 40 N).

The shaft 102 is pressed to one side and held by this spring resultant force Fb. Therefore, in the actuator 100, when no current is applied, the spring resultant force Fb to one side serves as the holding force for the shaft 102.

Therefore, even if an external force Fc (see FIG. 2(b)) that exceeds the spring resultant force Fb (e.g., 40 N) acts on the shaft 102 from one side to the other, if the external force Fc is equal to or less than the adsorption holding force Fa (e.g., 100 N), the movable iron core 110 is adsorbed to the fixed iron core 108, and the external force Fc is absorbed by the pair of elastic bodies 112a, 112b. Here, the external force Fc is, for example, an external force with a small displacement but a large force, such as vibration.

Therefore, according to the actuator 100, when an external force Fc is applied, the force that moves the movable yoke 118 is not the external force Fc acting directly, but the spring resultant force Fb acting indirectly. If the external force Fc is greater than the spring resultant force Fb, the shaft 102 moves. When the shaft 102 moves, the spring resultant force Fb increases, but if the spring resultant force Fb is smaller than the adsorption holding force Fa, the movable yoke 118 does not move and the shaft 102 returns to its original position. Even if the external force Fc is greater than the adsorption holding force Fa, the movable yoke 118 does not move if the amount of displacement is small, such as in the case of vibration, and the spring resultant force Fb does not exceed the adsorption holding force Fa. However, the movable yoke 118 moves only when the external force Fc is greater than the adsorption holding force Fa and the amount of displacement is so large that the spring resultant force Fb exceeds the adsorption holding force Fa. Therefore, in the actuator 100, the attraction and holding force Fa due to the magnetic flux Ra of the pair of magnets 120a, 120b can be small, which allows the pair of magnets 120a, 120b to be made smaller and less expensive.

Figure 3 is a diagram illustrating the state of the actuator 100 in Figure 1 when it is energized. Figure 3(a) shows the actuator 100 in the non-energized state shown in Figure 2(a) with current flowing through the coil 106 to excite it.

When energized, the magnetic flux Rb of the coil 106 shown in FIG. 3(a) generates a force Fd (e.g., 108 N) that attracts the movable core 110 to the other side. This force Fd is stronger than the attraction and holding force Fa (e.g., 100 N) of the magnetic flux Ra (dotted lines in the figure) of the pair of magnets 120a, 120b that attracted the stroke end 128a of the movable core 110 to one end face 116a of the fixed core 108.

Therefore, the force Fd cancels out the adhesive holding force Fa, and generates an adhesive force that attracts the movable iron core 110 to the other side. Therefore, the adhesive force is determined by the difference between the force Fd and the adhesive holding force Fa. Note that, for convenience, in the following, it is assumed that the adhesive force is determined by the difference between the force Fd (108 N) and the adhesive holding force Fa (100 N), and each calculation is performed assuming the value of the adhesive force to be 8 N as an example.

At this time, the elastic body 112a on one side, which was compressed when not energized, pushes the movable core 110 from one side to the other. Therefore, when energized, the spring resultant force Fb can assist the suction force when the movable core 110 separates from the fixed core 108. Therefore, the thrust acting on the shaft 102 when energized is the sum of the spring resultant force Fb (40 N) and the suction force (8 N) determined by factors such as the difference between the force Fd (108 N) and the suction holding force Fa (100 N) (here, 48 N).

In the actuator 100, even if the movable core 110 starts to move (see arrow α in FIG. 3(b)), the shaft 102 does not move as long as the elastic body 112a on the starting side is compressed.

Next, as shown in FIG. 3(b), when the movable core 110 moves to the other side (see arrow α) and the stroke end 128a of the movable core 110 moves away from one end face 116a of the fixed core 108, the attraction force Fa caused by the magnetic flux Ra of the pair of magnets 120a, 120b rapidly weakens. As a result, the attraction force to the other side, which is the difference between the force Fd and the attraction force Fa, becomes stronger, and the movable core 110 is attracted to the other side.

In addition, as the movable iron core 110 moves to the other side, the amount of displacement of the pair of elastic bodies 112a, 112b decreases (the amount of compression of the elastic body 112a on one side decreases, and the amount of extension of the elastic body 112b on the other side decreases), and the difference in the amount of displacement between the elastic bodies 112a, 112b on one side and the other side decreases, and the resultant spring force Fb to one side, which is the difference in elastic forces, approaches 0.

When the movable core 110 moves further to the other side as shown in FIG. 3(c) (see arrow α), the elastic body 112b on the other side is compressed and the elastic body 112a on one side is expanded, so that the difference in the amount of displacement between the elastic bodies 112a, 112b on one side and the other side becomes large again, and the resultant spring force Fb to the other side becomes large. When the elastic body 112b on the destination side begins to be compressed, a thrust is also generated in the shaft 102. However, if the thrust acting on the shaft 102 is smaller than the opposing load Fe (e.g., 70 N) from the other side to the one side, the movable core 110 continues to move to the other side (see arrow α in FIG. 3(b)), but the shaft 102 does not move yet.

When current is applied to the actuator 100, the movable core 110 first moves to the other side (see arrow α), and when the resultant spring force Fb becomes greater than the opposing load (e.g., 70 N), the shaft 102 starts to move to the other side, as shown by arrow β in FIG. 3(c). When current is applied to the actuator 100, immediately after the movable core 110 starts to move away, the elastic body 112b on the moving side (other side) of the movable core 110 is first compressed, and then the shaft 102 can be moved.

In this way, with the actuator 100, when current is applied, there is no need to move the shaft 102 to start moving the movable iron core 110 (there is no need to overcome the opposing load), so the movable iron core 110 can be moved by the force Fd generated by the weak magnetic flux Rb of the coil 106.

Furthermore, once the movable core 110 starts to move, the attraction and holding force Fa due to the magnetic flux Ra of the pair of magnets 120a, 120b weakens rapidly, so that when the shaft 102 is moved (overcoming the opposing load), the attraction and holding force Fa is significantly reduced. Therefore, according to the actuator 100, the force Fd due to the magnetic flux Rb of the coil 106 can be small, so that the coil 106 can be made smaller and less expensive.

Figure 4 is a graph showing the characteristics of the actuator 100 in Figure 1. Figure 4(a) shows the relationship between the displacement of the movable iron core 110 and the thrust acting on the shaft 102. The horizontal axis represents the distance between the stroke end 128a of the movable iron core 110 and one end face 116a of the fixed iron core 108.

Graph A in FIG. 4(a) shows the resultant spring force Fb acting on the shaft 102 when the movable core 110 is displaced. As shown in graph A, when the displacement of the movable core 110 is 0, the resultant spring force Fb acts to press the shaft 102 to one side (leftward), and when the displacement of the movable core 110 is 0.1 mm, the difference in the amount of displacement of the elastic bodies 112a, 112b on one side and the other side disappears, the natural length (neutral position) is reached, and the resultant spring force Fb becomes 0.

Then, until the displacement of the movable core 110 becomes from 0.1 mm to approximately 0.3 mm, the resultant spring force Fb acts to press the shaft 102 to the other side (to the right). This resultant spring force Fb to the other side occurs when, as described above, the elastic body 112b on the other side is compressed and the elastic body 112a on one side is expanded, causing the difference in the amount of displacement between the elastic bodies 112a, 112b on one side and the other side to increase again.

When the resultant spring force Fb exceeds the opposing load (70 N) at point B, the shaft 102 begins to be pushed to the other side. Furthermore, when the displacement of the movable core 110 exceeds approximately 0.3 mm at point C, the shaft 102 begins to move to the other side, and the difference in the amount of displacement between the elastic bodies 112a and 112b on one side and the other side is maintained, and the resultant spring force Fb becomes constant.

Graph D (dotted line in the figure) shows the attractive force that attracts the movable iron core 110 to the other side when current is applied. As described above, this attractive force is determined by factors such as the difference between the force Fd (108 N) due to the magnetic flux Rb of the coil 106 and the attraction and holding force Fa (100 N) due to the magnetic flux Ra of the pair of magnets 120a, 120b. As a result, this attractive force is 8 N when the displacement of the movable iron core 110 is 0.

Also, arrow E indicates assistance from the resultant spring force Fb (40 N). The resultant spring force Fb (40 N) assists the attractive force when the movable core 110 separates from the fixed core 108 when current is applied. Therefore, when the displacement of the movable core 110 is 0, the thrust acting on the shaft 102 is the sum (48 N) of the resultant spring force Fb (40 N) toward the other side and the attractive force (8 N), as shown at point F.

Therefore, with the actuator 100, when current is applied, the movable core 110 can be moved with a weak suction force (8 N) when the movable core 110 starts to move (when the displacement of the movable core 110 is 0).

In addition, the attraction force, which is the difference between force Fd and the attraction holding force Fa, is constant due to the magnetic flux Rb of the coil 106, but the greater the displacement of the movable iron core 110, the more rapidly the attraction holding force Fa weakens. Therefore, as shown in graph D, the greater the displacement of the movable iron core 110, the stronger the attraction force becomes, and the movable iron core 110 is attracted to the other side.

Graph G (solid line in the figure) shows the thrust acting on the shaft 102 after point H, i.e. when the displacement of the movable core 110 exceeds approximately 0.3 mm and the movable core 110 moves with the shaft 102. This thrust exceeds the mating load (70 N), and as the displacement of the movable core 110 increases further, the adhesive holding force Fa weakens, so the thrust becomes stronger as shown in graph G.

Figure 4 (b) shows the relationship between the stroke of the shaft 102 and the holding force when no current is applied. The horizontal axis represents the distance between the holding member 122a on one side of the shaft 102 and the side plate 126a of the casing 102.

Each arrow Ja-Jd indicates the resultant spring force Fb acting on one side of the shaft 102 when the movable core 110 is attracted to the fixed core 108 when not energized. The movable core 110 is attracted to the fixed core 108 by the attraction and holding force Fa (100 N) generated by the magnetic flux Ra of the pair of magnets 120a, 120b.

When the stroke of the shaft 102 is 0, as shown by the arrow Ja, the resultant spring force Fb presses the shaft 102 to one side with 40 N and holds it in place. Also, when the shaft 102 receives an external force such as vibration exceeding 40 N (an external force with a small amount of displacement and a large force) while not energized and moves to the other side, the more the shaft 102 moves to the other side, as shown by the arrows Jb, Jc, and Jd, the stronger the resultant spring force Fb becomes.

Graph K, which connects the vertices of the arrows Ja-Jd, shows the attraction and retention force Fa of the shaft 102 when no current is applied. According to graph K, even if an external force exceeding 40 N acts on the shaft 102 from one side to the other when no current is applied, the external force is absorbed by the pair of elastic bodies 112a, 112b as long as it is equal to or less than the attraction and retention force Fa (100 N).

On the other hand, graph L (dotted line in the figure) is a comparative example, and shows the holding force due to the permanent magnets only (a state in which the movable yoke 118 and shaft 102 are fixed together). In this comparative example, when the shaft 102 moves to the other side, the movable iron core 110 also moves away from the fixed iron core 108. For this reason, in the comparative example, the holding force of the shaft 102, i.e., the attraction holding force Fa due to the magnetic flux Ra of the pair of magnets 120a, 120b, weakens rapidly as the shaft 102 moves to the other side. Therefore, in the comparative example, the shaft 102 cannot fully absorb the external force it receives, and it becomes difficult to return the shaft 102 to its original position.

In contrast, with the actuator 100 of the present invention, the external force is absorbed by the pair of elastic bodies 112a, 112b, so that the resultant spring force Fb to one side can return the shaft 102 to its original position.

In the actuator 100, the movable core 110 has a pair of magnets 120a, 120b, but this is not limiting. As an example, the pair of magnets 120a, 120b may be arranged on the fixed core 108 side, and the movable core 110 may be held by the stroke ends 128a, 128b on both sides (see, for example, Patent Document 1 mentioned above). In this example, the slit 114 of the fixed core 108 is not necessary, and the movable yoke 118 of the movable core 110 does not need to protrude radially so as to be arranged between the slits 114, simplifying the structure of the movable core 110.

Although the preferred embodiment of the present invention has been described above with reference to the attached drawings, it goes without saying that the present invention is not limited to such an example. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

The present invention can be used as a bidirectional actuator that can actively move a shaft in both directions.

100...actuator, 102...shaft, 104...casing, 106...coil, 108...fixed iron core, 110...movable iron core, 112a, 112b...pair of elastic bodies, 114...slit of fixed iron core, 116a...one end face of fixed iron core, 116b...other end face of fixed iron core, 118...movable yoke, 120a, 120b...pair of magnets, 122a, 122b...pair of holding members, 124a...one end of movable iron core, 124b...other end of movable iron core, 126a, 126b...side plate of casing, 128a, 128b...stroke end of movable iron core

Claims (1)

A cylindrically wound coil;
A fixed core covering the coil;
a movable core that moves in both directions in the axial direction of the coil inside the fixed core;
A pair of magnets that hold the movable core at both stroke ends;
a shaft that slidably passes through the inside of the movable iron core;
a pair of holding members provided on the shaft, each protruding from either side of the movable core at a predetermined distance and capable of contacting the fixed core;
a pair of elastic bodies respectively disposed between the pair of holding members and both sides of the movable iron core.

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