Linear motion actuator and electromagnetic suspension

Abstract

To ease impact and high frequency vibration with elements provided in a linear motion actuator without needing an additional device for controlling.SOLUTION: A linear motion actuator includes: a feed screw configured to be rotated; a nut member which has two end surfaces and is linearly moved along a feed screw axis direction as the feed screw rotates; a linear motion cylindrical member which is disposed around the nut member, has a length along an axial direction which is longer than a length of the nut member, and is linearly moved with the nut member; two annular members which are formed of a rigid material, respectively disposed so as to face the end surfaces of the nut member, engaged with the linear motion cylindrical member to transmit linear motion of the nut member to the linear motion cylindrical member; and two first annular buffer members each of which is formed of an elastomer material, disposed between the annular member and the end surface of the nut member, and compressed between the annular member and the end surface of the nut member.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a linear actuator and an electromagnetic suspension. [Background technology]

[0002] Conventionally, electromagnetic suspensions having a linear actuator and a spring have been developed (Patent Documents 1 and 2). It is preferable for a suspension to be able to absorb shock as much as possible. In particular, when a large shock is applied to this type of electromagnetic suspension, an excessive load is placed on the linear actuator and the motor that drives it. It is also preferable for the suspension to be able to absorb not only shock but also high-frequency vibration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-132298 A [Patent Document 2] JP 2005-096587 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology disclosed in Patent Document 1, when an excessive rotational force is applied to the motor, the force fixing the motor is weakened to allow the motor itself to rotate, thereby preventing damage to the motor and other components. However, this technology measures the displacement and acceleration of the vehicle body, and controls the force fixing the motor based on the displacement speed and acceleration. Therefore, a sensor for measurement and an electronic control device are required.

[0005] In the technology disclosed in Patent Document 2, the rigidity of the shock absorbing means is variable, and the acceleration of the vehicle body is measured and the rigidity of the shock absorbing means is controlled based on the acceleration. Therefore, a sensor for measurement and an electronic control device are required. In addition, the technology disclosed in Patent Document 2 cannot mitigate the shock applied to the inside of the linear actuator.

[0006] Therefore, the present invention provides a technique for mitigating shock and high-frequency vibration by an element provided in a linear actuator, without requiring an additional device for control. [Means for solving the problem]

[0007] One aspect of the present invention provides a linear actuator, comprising: a feed screw that is rotated; a nut member that has two end faces and is moved linearly along the axial direction of the feed screw as the feed screw rotates; a linear cylindrical member that is arranged around the nut member, has a length along the axial direction greater than that of the nut member, and is moved linearly together with the nut member; two annular members that are made of a rigid material and arranged to face the end faces of the nut member, engage with the linear cylindrical member, and transmit the linear motion of the nut member to the linear cylindrical member; and two annular first buffer members that are made of an elastomer material and arranged between the annular member and the end face of the nut member and are compressed between the annular member and the end face of the nut member.

[0008] Another aspect of the present invention provides an electromagnetic suspension, comprising: the linear actuator further having a cylindrical guide sleeve disposed outside the linear cylindrical member and extending along the axial direction to guide the linear motion of the linear cylindrical member; a first mounting portion connected to the linear cylindrical member and attached to one member of a structure; a second mounting portion connected to the guide sleeve and attached to the other member of the structure; a first load support plate engaging with the linear cylindrical member; a second load support plate engaging with the guide sleeve; and a coil spring disposed between the first load support plate and the second load support plate and compressed between the first load support plate and the second load support plate. Effect of the Invention

[0009] In an embodiment of the present invention, two annular members are engaged with a linear cylindrical member that is moved linearly together with a nut member, and an annular first buffer member made of an elastomer material is interposed between each annular member and the end face of the nut member. Thus, the linear cylindrical member can move slightly along the axial direction relative to the nut member while expanding and contracting the first buffer member, and the first buffer member absorbs the impact and high-frequency vibration applied to the linear cylindrical member mainly along the axial direction. Therefore, the impact and high-frequency vibration applied to the linear cylindrical member are not easily transmitted to the nut member, and thus to the feed screw and the rotary drive device for rotating it. In this way, no additional device for control is required, and the impact and high-frequency vibration are absorbed by the two first buffer members provided in the linear actuator, protecting the nut member, the feed screw, and the rotary drive device from the impact and high-frequency vibration. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a front cross-sectional view showing an electromagnetic suspension having a linear actuator according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a side cross-sectional view of the electromagnetic suspension of FIG. [Diagram 3]FIG. 3 is a cross-sectional front view of the electromagnetic suspension of FIG. 1 in a retracted state. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a portion of FIG. [Diagram 5] FIG. 5 is an enlarged cross-sectional view showing the same part as in FIG. 4 according to a modified example. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing the same part as in FIG. 4 according to another modified example. [Figure 7] FIG. 7 is a bottom view of the feed screw of the linear actuator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Various embodiments of the present invention will now be described with reference to the accompanying drawings, in which the drawings are not necessarily drawn to scale and some features may be exaggerated or omitted.

[0012] As shown in FIGS. 1 to 3, an electromagnetic suspension 1 according to an embodiment of the present invention has a linear actuator 2.

[0013] The linear actuator 2 has a motor 3 , a motor driver 4 , a gear transmission mechanism 5 , a feed screw 6 , a nut member 7 , a linear cylindrical member 8 , and a housing 9 .

[0014] The motor 3 is, for example, a servo motor or a stepping motor. The motor 3 has a rotating shaft 3a. The motor driver 4 controls the rotation of the rotating shaft 3a. A signal is supplied to the motor driver 4 from an acceleration sensor (not shown) that measures the acceleration applied to the electromagnetic suspension 1, and the motor driver 4 controls the rotation of the rotating shaft 3a based on the signal from the acceleration sensor, so that the linear actuator 2 exerts a vibration damping function.

[0015] The motor 3 is fixed to a housing 9, and the rotating shaft 3a passes through a hole formed in a flange 9a of the housing 9. The housing 9 is made of a rigid material such as metal or resin.

[0016] The gear transmission mechanism 5 is driven by a rotating shaft 3a of the motor 3. The gear transmission mechanism 5 has two gears 10 and 11. The gears 10 and 11 are, for example, spur gears, but may also be helical gears.

[0017] The gear 10 is a drive gear, and is fixed to the rotating shaft 3a to rotate together with the rotating shaft 3a. For example, the gear 10 is fixed to the rotating shaft 3a by a key 3b and a nut 3c.

[0018] Gear 11 is a driven gear that meshes with gear 10 and is driven to rotate by gear 10. Gear 11 is fixed to a rotating shaft 11a and rotates together with the rotating shaft 11a. For example, gear 11 is fixed to the rotating shaft 11a by a key 11b and a nut 11c.

[0019] The rotating shaft 11a is rotatably supported by rolling bearings 12 and 13. The rolling bearings 12 and 13 are supported by a bearing housing 14, and the bearing housing 14 is fixed to a flange 9a of the housing 9.

[0020] A cover 15 is fixed to the flange 9a of the housing 9. The cover 15 is formed from a rigid material such as metal or resin, and together with the housing 9, defines a space for accommodating the gear transmission mechanism 5 and protects the gear transmission mechanism 5. In addition to the flange 9a, the housing 9 has a cylindrical guide sleeve 9b that guides the linear motion of the linear motion cylindrical member 8. The guide sleeve 9b is integrally connected to the flange 9a.

[0021] In this embodiment, the rotating shaft 11a of the gear 11 is the output shaft of the gear transmission mechanism 5, and the feed screw 6 of the linear actuator 2 is formed on an extension of the rotating shaft 11a. Therefore, the feed screw 6 is rotated about its own axial direction as the rotating shaft 3a of the motor 3 rotates.

[0022] The feed screw 6 is arranged coaxially with the guide sleeve 9b. The feed screw 6 may be a trapezoidal screw, a ball screw (e.g., a circulating ball screw), or any of various roller screws. The roller screw may be, for example, a planetary roller screw, a circulating roller screw, or any other roller screw.

[0023] The nut member 7 is engaged with the feed screw 6, and is moved straight along the axial direction of the feed screw 6 as the feed screw 6 rotates. The nut member 7 is made of a rigid material such as metal or resin. The nut member 7 has a cylindrical contour and has an outer circumferential surface 7a and end faces 7b and 7c.

[0024] The linear motion cylindrical member 8 is disposed around the nut member 7 and engaged with the nut member 7, and is moved linearly together with the nut member 7 along the axial direction of the feed screw 6 as the feed screw 6 rotates. However, as described later, the linear motion cylindrical member 8 can move slightly along the axial direction of the feed screw 6 relative to the nut member 7. The linear motion cylindrical member 8 can also be called a linear rod.

[0025] The linear motion cylindrical member 8 is a cylindrical pipe made of a rigid material such as metal or resin, and the length of the linear motion cylindrical member 8 along the axial direction of the feed screw 6 is greater than that of the feed screw 6. The linear motion cylindrical member 8 is arranged coaxially with the feed screw 6 and the guide sleeve 9b. The linear motion cylindrical member 8 is arranged in the internal space of the guide sleeve 9b so as to be capable of reciprocating along the axial direction. The feed screw 6 extends through the center of the internal space of the linear motion cylindrical member 8.

[0026] A key 16 is fixed to the nut member 7, and a key groove 17 into which the key 16 is fitted is formed in the linear motion cylindrical member 8 (the key groove 17 is shown by an imaginary line in Figs. 1 and 3). The key 16 fixed to the nut member 7 comes into contact with the linear motion cylindrical member 8 in the circumferential direction centered on the axis of the feed screw 6, thereby preventing the nut member 7 from rotating around the feed screw 6.

[0027] The linear motion cylindrical member 8, which is a cylindrical pipe, has an end wall 8a at its end. The linear motion cylindrical member 8 has a closed space (second space) 8b surrounded by the end wall 8a, the peripheral wall of the linear motion cylindrical member 8, and the nut member 7. The closed space 8b is the space on the end wall 8a side, where the nut member 7 is not disposed, within the internal space of the linear motion cylindrical member 8. The volume of the closed space 8b varies with the linear motion of the nut member 7.

[0028] The cylindrical guide sleeve 9b, which guides the linear motion of the linear motion cylindrical member 8, is disposed outside the linear motion cylindrical member 8 and extends along the axial direction of the feed screw 6. The guide sleeve 9b has a closed space (first space) 9c surrounded by the rolling bearing 13, the bearing housing 14, the peripheral wall of the guide sleeve 9b, and the nut member 7. The closed space 9c is the space on the rolling bearing 13 side, where the nut member 7 is not disposed, within the internal space of the guide sleeve 9b. The feed screw 6 extends through the center of the closed space 9c. The volume of the closed space 9c varies with the linear motion of the nut member 7.

[0029] The linear actuator 2 used in the electromagnetic suspension 1 has an end wall 8a of a linear cylindrical member 8, to which an end mounting portion (first mounting portion) 20 is integrally connected.

[0030] On the other hand, an end attachment portion (second attachment portion) 21 is integrally connected to the cover 15 connected to the guide sleeve 9b.

[0031] The linear actuator 2 can be used in an electromagnetic suspension 1 for vertical vibration suppression of a transportation device or a building. In this case, the linear actuator 2 is arranged in a position in which the end mounting portion 21 is located at the top and the end mounting portion 20 is located at the bottom, as shown in Figs. 1 to 3. The end mounting portion 20 is attached to a portion 22 of the transportation device or the building, for example, with a bolt 23 and a nut 24. The end mounting portion 21 is attached to another portion 25 of the transportation device or the building, for example, with a bolt 26 and a nut 27. When the linear actuator 2 is used in a transportation device in this manner, the portion 25 is on the vehicle body side, and the portion 22 is on the wheel side below the vehicle body.

[0032] The linear actuator 2 can be used in an electromagnetic suspension 1 for lateral vibration suppression of transportation equipment (e.g., a railroad car) or a building. In this case, the feed screw 6, the nut member 7, the linear cylindrical member 8, and the guide sleeve 9b are arranged in an orientation in which their longitudinal directions are lateral. Then, the end mounting portion 20 is attached to a portion 22 which is one side of the equipment or the building, and the end mounting portion 21 is attached to a portion 25 which is the other side of the equipment or the building.

[0033] 3 shows the retracted state of the linear actuator 2 (more precisely, the retracted state of the linear cylindrical member 8). In this manner, the feed screw 6, which is an extension of the rotating shaft 11a, is rotated by the gear transmission mechanism 5, and the nut member 7 and the linear cylindrical member 8 are caused to move linearly in accordance with the rotation of the feed screw 6.

[0034] When the gear transmission mechanism 5 is rotated in the reverse direction, the linear motion cylindrical member 8 is extended, in the opposite manner to that shown in Fig. 3. In this manner, the linear motion cylindrical member 8 is caused to reciprocate.

[0035] The range (stroke) in which the linear motion cylindrical member 8 can move linearly is finite, and therefore the motor 3 is controlled by the motor driver 4 so as to rotate within a finite angular range. Therefore, the gears 10 and 11 of the gear transmission mechanism 5 also rotate within a limited angular range.

[0036] Although not absolutely necessary, in order to facilitate the linear motion of the linear cylindrical member 8, plain bearings 28, 29 are interposed between the outer peripheral surface of the linear cylindrical member 8 and the inner peripheral surface of the guide sleeve 9b. The plain bearings 28, 29 are, for example, cylindrical bushings. However, each of the plain bearings 28, 29 may be a split plain bearing having multiple arc-shaped pieces.

[0037] In this embodiment, the plain bearing 28 is disposed in a circumferential groove formed on the outer circumferential surface of the linear motion cylindrical member 8. The outer circumferential surface of the plain bearing 28 is in slidable contact with the inner circumferential surface of the guide sleeve 9b. The plain bearing 29 is disposed in a circumferential groove formed on the inner circumferential surface of the guide sleeve 9b. The inner circumferential surface of the plain bearing 29 is in slidable contact with the outer circumferential surface of the linear motion cylindrical member 8.

[0038] In order to transmit the linear motion of the nut member 7 to the linear motion cylindrical member 8, two circular ring members 30, 31 are provided which engage with the nut member 7 and the linear motion cylindrical member 8. The circular ring members 30, 31 are formed from a rigid material such as metal or resin. The circular ring member 30 faces an end face 7b of the nut member 7 on the cover 15 side of the end attachment portion 20 side, and the circular ring member 31 faces an end face 7c of the nut member 7 on the end attachment portion 21 side.

[0039] 4, the circular members 30 and 31 are fitted into circumferential grooves formed on the inner circumferential surface of the linear motion cylindrical member 8 and fixed to the linear motion cylindrical member 8. The circular members 30 and 31 are, for example, C-type retaining rings.

[0040] Since the circular ring member 30 is fixed to the linear motion cylindrical member 8 and faces the end face 7b of the nut member 7, and the circular ring member 31 is fixed to the linear motion cylindrical member 8 and faces the end face 7c of the nut member 7, the linear motion cylindrical member 8 can move linearly together with the nut member 7 along the axial direction of the feed screw 6 as the feed screw 6 rotates. In other words, the circular ring members 30 and 31 transmit the linear motion of the nut member 7 to the linear motion cylindrical member 8.

[0041] However, in order to reduce the impact and high-frequency vibration applied to the linear actuator 2, two annular axial buffer members (first buffer members) 32, 33 made of an elastomer material are brought into contact with both end faces 7b, 7c of the nut member 7.

[0042] The axial buffer member 32 is interposed between the circular member 30 and the end face 7b of the nut member 7, and is compressed between the circular member 30 and the end face 7b of the nut member 7. The axial buffer member 33 is interposed between the circular member 31 and the end face 7c of the nut member 7, and is compressed between the circular member 31 and the end face 7c of the nut member 7.

[0043] The axial buffer members 32, 33 are, for example, O-rings. However, the axial buffer members 32, 33 may be X-rings having an X-shaped cross section, D-rings having a D-shaped cross section, or rings having a rectangular cross section.

[0044] In this manner, the two annular members 30, 31 are engaged with the linear motion cylindrical member 8, and annular axial buffer members 32, 33 made of an elastomer material are interposed between the respective annular members 30, 31 and the end faces 7b, 7c of the nut member 7. Therefore, the linear motion cylindrical member 8 can move slightly (by the amount of expansion and contraction of the axial buffer members 32, 33) along the axial direction of the feed screw 6 relative to the nut member 7 while expanding and contracting the axial buffer members 32, 33.

[0045] 4, the key 16 has a length along the axial direction of the feed screw 6 that is shorter than the length of the key groove 17. Therefore, the key 16 and the key groove 17 allow the linear motion cylindrical member 8 relative to the nut member 7 to move along the axial direction.

[0046] The axial buffer members 32, 33 mainly absorb the impact and high-frequency vibration applied to the linear cylindrical member 8 along the axial direction of the feed screw 6. Therefore, the impact and high-frequency vibration applied to the linear cylindrical member 8 from the part 22 of the transportation equipment or building through the end mounting part 20 is not easily transmitted to the nut member 7, the feed screw 6, the gear transmission mechanism 5 for its rotation, and the motor 3. In this way, no additional device for control is required, and the impact and high-frequency vibration are absorbed by the two axial buffer members 32, 33 provided in the linear actuator 2, and the nut member 7, the feed screw 6, the gear transmission mechanism 5 for its rotation, and the motor 3 are protected from the impact and high-frequency vibration.

[0047] For example, when the end attachment part 21 is attached to the part 25 on the vehicle body side of the transport equipment and the end attachment part 20 is attached to the part 22 on the wheel side, the impact and high-frequency vibration applied to the linear motion cylindrical member 8 through the end attachment part 20 from the road surface on which the transport equipment runs are not easily transmitted to the nut member 7, and further to the feed screw 6, the gear transmission mechanism 5 for rotating the feed screw 6, and the motor 3. This improves the ride comfort of the passengers of the transport equipment.

[0048] The axial buffer members 32, 33 have an inner diameter D larger than the maximum diameter d of the feed screw 6 in a state where they are compressed between the annular members 30, 31 and the end faces 7b, 7c of the nut member 7. Therefore, even if the linear motion cylindrical member 8 is eccentric with respect to the feed screw 6, the axial buffer members 32, 33 can be prevented from contacting the feed screw 6. In addition, even if the linear motion cylindrical member 8 is bent, the axial buffer members 32, 33 can be prevented from contacting the feed screw 6. Therefore, twisting or bending of the feed screw 6 can be suppressed, and wear of the axial buffer members 32, 33 can be suppressed.

[0049] As shown in the enlarged cross-sectional view of FIG. 4, a small annular gap 35 is provided between the outer peripheral surface 7a of the nut member 7 and the inner peripheral surface of the linear motion cylindrical member 8. The key 16 is fixed to the linear motion cylindrical member 8 by being fitted into a groove formed in the outer peripheral surface 7a of the nut member 7, and is fitted into the linear motion cylindrical member 8. However, the key 16 does not contact the linear motion cylindrical member 8 in the radial direction centered on the axis of the feed screw 6. More specifically, a key groove 17 formed in the linear motion cylindrical member 8 and into which the key 16 is fitted penetrates the wall of the linear motion cylindrical member 8 in the radial direction.

[0050] A small annular gap 35 is provided between the outer peripheral surface 7a of the nut member 7 and the inner peripheral surface of the linear cylindrical member 8, and the key 16 does not contact the linear cylindrical member 8 in the radial direction. Therefore, even if the linear cylindrical member 8 is eccentric with respect to the feed screw 6, the eccentricity of the linear cylindrical member 8 is not transmitted from the key 16 to the nut member 7. Even if the linear cylindrical member 8 is bent, the radial displacement of the linear cylindrical member 8 is not transmitted from the key 16 to the nut member 7. Therefore, the axial buffer members 32, 33 that are in close contact with the nut member 7 are prevented from contacting the feed screw 6. Therefore, the twisting or bending of the feed screw 6 can be suppressed, and the wear of the axial buffer members 32, 33 can be suppressed.

[0051] In order to prevent the key 16 from contacting the linear cylindrical member 8 in the radial direction centered on the axis of the feed screw 6, the key groove 17 does not necessarily have to penetrate the wall of the linear cylindrical member 8. However, by having the key groove 17 penetrate the wall of the linear cylindrical member 8 in the radial direction as in this embodiment, it is easy to insert the key 16 into the key groove 17 from the outside of the linear cylindrical member 8 and further fix it to the nut member 7.

[0052] The linear actuator 2 further includes at least one annular radial buffer member (second buffer member) 38. In this embodiment, two radial buffer members 38 are provided, but the number of radial buffer members 38 is not limited.

[0053] The radial buffer member 38 is formed from an elastomer material and is positioned radially outside the nut member 7 and radially inside the linear motion cylindrical member 8. The radial buffer member 38 comes into contact with the nut member 7 and the linear motion cylindrical member 8 to close the annular gap 35.

[0054] 4, two circumferential grooves 40 are formed on the inner circumferential surface of the linear motion cylindrical member 8, and each radial buffer member 38 is disposed inside the circumferential groove 40. Each radial buffer member 38 contacts the wall surface of the circumferential groove 40 and also contacts the outer circumferential surface 7a of the nut member 7.

[0055] An annular gap 35 is provided between the inner peripheral surface of the linear motion cylindrical member 8 and the outer peripheral surface of the nut member 7, and the annular gap 35 is closed by an annular radial buffer member 38. The radial buffer member 38 eliminates the gap 35 and prevents the inner peripheral surface of the linear motion cylindrical member 8 from contacting the outer peripheral surface of the nut member 7, so that even if the linear motion cylindrical member 8 moves relative to the nut member 7, neither the linear motion cylindrical member 8 nor the nut member 7 is worn.

[0056] In addition, since the radial buffer member 38 surrounds the nut member 7 and is disposed radially inside the linear motion cylindrical member 8, even if the linear motion cylindrical member 8 is eccentric with respect to the feed screw 6, the influence of the radial position of the linear motion cylindrical member 8 on the nut member 7 is reduced. Even if the linear motion cylindrical member 8 is bent, the radial displacement of the linear motion cylindrical member 8 is absorbed by the radial buffer member 38 and is not easily transmitted to the nut member 7. For this reason, the axial buffer members 32, 33, which are in close contact with the nut member 7, are prevented from contacting the feed screw 6. Therefore, it is possible to suppress twisting or bending of the feed screw 6 and to suppress wear of the axial buffer members 32, 33.

[0057] In the embodiment, the radial buffer member 38 is an O-ring, but may be another ring, such as an X-ring, a D-ring, or the like.

[0058] 5, in a modification of the embodiment, a circumferential groove 41 may be formed on the outer circumferential surface 7a of the nut member 7, and each radial buffer member (second buffer member) 42 may be disposed inside the circumferential groove 41. Each radial buffer member 42 contacts the wall surface of the circumferential groove 41 and also contacts the inner circumferential surface of the linear motion cylindrical member 8.

[0059] 5, the radial buffer members 42 are D-rings made of an elastomeric material, but may be other rings, such as X-rings, O-rings, etc. In this modification, two radial buffer members 42 are provided, but the number of radial buffer members 42 is not limited.

[0060] 6, in another modified example of the embodiment, both the circumferential groove 41 of the nut member 7 and the circumferential groove 40 of the linear motion cylindrical member 8 may be omitted, and each radial buffer member (second buffer member) 44 may be disposed between the outer circumferential surface 7a of the nut member 7 and the inner circumferential surface of the linear motion cylindrical member 8. Each radial buffer member 44 contacts the outer circumferential surface 7a of the nut member 7 and also contacts the inner circumferential surface of the linear motion cylindrical member 8.

[0061] 6, the radial buffer members 44 are cylindrical rings made of an elastomeric material, but may be other rings, such as X-rings, D-rings, O-rings, etc. In this modification, two radial buffer members 44 are provided, but the number of radial buffer members 44 is not limited.

[0062] As described above, as shown in Figs. 1 to 3, annular axial buffer members 32, 33 made of an elastomer material are disposed near both end faces 7b, 7c of the nut member 7. The axial buffer member 32 is compressed between the annular member 30 and the end face 7b of the nut member 7. The axial buffer member 33 is compressed between the annular member 31 and the end face 7c of the nut member 7. A small annular gap 35 is provided between the outer peripheral surface 7a of the nut member 7 and the inner peripheral surface of the linear motion cylindrical member 8, but the gap 35 is closed by annular radial buffer members 38, 42 or 44 made of an elastomer material.

[0063] The axial buffer members 32, 33 and the radial buffer members 38, 42 or 44 obstruct the flow of air between the closed space 9c surrounded by the guide sleeve 9b and in which the nut member 7 is not disposed, and the closed space 8b surrounded by the linear cylindrical member 8 and in which the nut member 7 is not disposed. As described above, the linear cylindrical member 8 can move slightly along the axial direction relative to the nut member 7 while expanding and contracting the axial buffer members 32, 33. However, if the flow of air between the closed space 9c and the closed space 8b is obstructed, the movement of the linear cylindrical member 8 relative to the nut member 7 is obstructed, and the axial buffer members 32, 33 may not be able to exhibit their buffering function well.

[0064] The feed screw 6 has a hollow structure having an internal hole 6a extending along the axial direction, and the internal hole 6a communicates with the closed space 9c and the closed space 8b. The internal hole 6a is concentric with the feed screw 6, but may be eccentric.

[0065] The internal hole 6a opens at the lower end of the feed screw 6 and communicates with the closed space 8b. As shown in Figures 1 to 3 and 7, the feed screw 6 has a radial hole 6b extending in the radial direction, and the radial hole 6b is connected to the upper end of the internal hole 6a. Therefore, the internal hole 6a communicates with the closed space 9c through the radial hole 6b.

[0066] The internal hole 6a of the feed screw 6 allows air to flow between the closed space 9c and the closed space 8b, thereby allowing the linear-acting cylindrical member 8 relative to the nut member 7 to move, and the axial buffer members 32, 33 can reliably perform their buffering function.

[0067] As shown in FIGS. 1 to 3, the electromagnetic suspension 1 further includes a coil spring 50 for absorbing an impact applied from one member of a structure to another member.

[0068] A first load support plate 51 is engaged with the linear motion cylindrical member 8 to which an impact is applied from the portion 22 shown in Figures 1 and 3, and a second load support plate 52 is engaged with the guide sleeve 9b connected to the portion 25. The second load support plate 52 is a ring through which the guide sleeve 9b passes. A flange 53 is formed on the guide sleeve 9b, and the upper surface of the second load support plate 52 is brought into contact with the lower surface of the flange 53.

[0069] The coil spring 50 is disposed between the first load support plate 51 and the second load support plate 52, and is compressed between the first load support plate 51 and the second load support plate 52. Therefore, the impact applied from the portion 22 is absorbed by the coil spring 50, and is not easily transmitted to the portion 25.

[0070] The coil spring 50 is disposed coaxially with the guide sleeve 9b, so that an offset load is unlikely to be applied to the guide sleeve 9b, and bending of the guide sleeve 9b is prevented.

[0071] However, the coil spring 50 is not absolutely necessary. Even if the coil spring 50 is not provided, the linear actuator 2 itself can be used as an electromagnetic suspension.

[0072] Other Variations Although the present invention has been shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that changes may be made in form and detail without departing from the scope of the invention as set forth in the appended claims. Such changes, modifications and alterations are intended to be embraced within the scope of the invention.

[0073] For example, in the above embodiment, the gears 10 and 11 of the gear transmission mechanism 5 are spur gears or helical gears, but a combination of bevel gears or a worm gear mechanism may be used as the gear transmission mechanism. Any number of gears may be provided in the gear transmission mechanism. In addition, the positions of the bearings supporting the rotating shafts to which the gears are attached may be changed, or bearings may be added.

[0074] The mechanism for transmitting the rotational motion of the motor to the feed screw 6 is not limited to a gear transmission mechanism, but may be, for example, a belt and pulley mechanism, and the belt may be a timing belt or a V-belt.

[0075] In the above embodiment, a rotation prevention mechanism (key 16) is provided for the nut member 7 relative to the linear cylindrical member 8, but no rotation prevention mechanism is provided for the linear cylindrical member 8 relative to the guide sleeve 9b. However, a rotation prevention mechanism (e.g., a key or spline) for the linear cylindrical member 8 relative to the guide sleeve 9b may be provided.

[0076] As described above, the linear actuator 2 is used for vibration damping of a structure (transportation equipment or a building). However, the application of the linear actuator 2 is not limited to vibration damping of a structure. The linear actuator according to the present invention may be used in other structures in which it is desirable to suppress shock or high-frequency vibration. [Explanation of symbols]

[0077] 1...Electromagnetic suspension. 2...Linear actuator. 5...Gear transmission mechanism. 6...Feed screw. 6a...Internal hole. 6b...Radial hole. 7...Nut member. 7a...Outer surface. 7b, 7c...End surface. 8...Linear cylindrical member. 8b...Closed space (second space). 9...Housing. 9b...Guide sleeve. 9c...Closed space (first space). 16...Key. 17...Key groove. 20...End mounting portion (first mounting portion). 21...End mounting portion (second mounting portion). 30, 31...Annular member. 32, 33...Axial buffer member (first buffer member). 35...Gap. 38, 42, 44...Radial buffer member (second buffer member). 50...Coil spring. 51...First load support plate. 52...Second load support plate

Claims

1. A feed screw that can be rotated; a nut member having two end faces and moved linearly along the axial direction of the feed screw as the feed screw rotates; a linear motion cylindrical member that is disposed around the nut member, has a length along the axial direction that is greater than a length of the nut member, and is moved linearly together with the nut member; two annular members formed of a rigid material, each disposed so as to face the end surface of the nut member, engaged with the linear motion cylindrical member, and transmitting the linear motion of the nut member to the linear motion cylindrical member; and two annular first buffer members formed from an elastomer material, disposed between the annular member and the end surface of the nut member, and compressed between the annular member and the end surface of the nut member. A linear actuator characterized by:

2. The first buffer member has an inner diameter larger than a maximum diameter of the feed screw when compressed between the annular member and the end surface of the nut member.

2. The linear actuator according to claim 1 .

3. an annular gap provided between an outer circumferential surface of the nut member and an inner circumferential surface of the linear motion cylindrical member; A key is further provided which is fixed to the nut member and fitted into the linear motion cylindrical member, The key does not contact the linear motion cylindrical member in a radial direction centered on the axis of the feed screw.

3. The linear actuator according to claim 2.

4. The linear motion cylindrical member has a key groove into which the key is fitted, and the key groove penetrates a wall of the linear motion cylindrical member in the radial direction.

4. The linear actuator according to claim 3.

5. An annular gap is provided between the inner peripheral surface of the linear motion cylindrical member and the outer peripheral surface of the nut member, and at least one annular second buffer member that is made of an elastomer material, that is disposed radially outside the nut member and radially inside the linear motion cylindrical member, that contacts the nut member and the linear motion cylindrical member, and that closes the gap.

5. The linear actuator according to claim 1, wherein the linear actuator is a linear actuator.

6. a cylindrical guide sleeve disposed outside the linear motion cylindrical member, extending along the axial direction, and guiding the linear motion of the linear motion cylindrical member; a first space surrounded by the guide sleeve, the lead screw being disposed at a center thereof, and the nut member not being disposed therein; a second space surrounded by the linear cylindrical member, the feed screw being disposed at a center thereof, and the nut member not being disposed therein; Each of the first space and the second space has a volume that varies with the translatory movement of the nut member, The feed screw has an internal hole extending along the axial direction, and the internal hole communicates with the first space and the second space.

5. The linear actuator according to claim 1, wherein the linear actuator is a linear actuator.

7. a cylindrical guide sleeve disposed outside the linear motion cylindrical member, extending along the axial direction, and guiding the linear motion of the linear motion cylindrical member; a first space surrounded by the guide sleeve, the lead screw being disposed at a center thereof, and the nut member not being disposed therein; a second space surrounded by the linear cylindrical member, the feed screw being disposed at a center thereof, and the nut member not being disposed therein; Each of the first space and the second space has a volume that varies with the translatory movement of the nut member, The feed screw has a hollow structure having an internal hole extending along the axial direction, and the internal hole communicates with the first space and the second space.

6. The linear actuator according to claim 5.

8. 5. The linear motion actuator according to claim 1, further comprising a cylindrical guide sleeve disposed outside the linear motion cylindrical member, extending along the axial direction, and guiding the linear motion of the linear motion cylindrical member; a first mounting portion connected to the linear cylindrical member and attached to one member of a structure; a second mounting portion coupled to the guide sleeve and adapted to be attached to another member of the structure; a first load support plate that engages with the linear motion cylindrical member; a second load bearing plate engaging the guide sleeve; a coil spring disposed between the first load support plate and the second load support plate and compressed between the first load support plate and the second load support plate. Electromagnetic suspension.

9. The linear actuator comprises: a first space surrounded by the guide sleeve, the lead screw being disposed at a center thereof, and the nut member not being disposed therein; a second space surrounded by the linear cylindrical member, the feed screw being disposed at a center thereof, and the nut member not being disposed therein; Each of the first space and the second space has a volume that varies with the translatory movement of the nut member, The feed screw has a hollow structure having an internal hole extending along the axial direction, and the internal hole communicates with the first space and the second space.

9. The electromagnetic suspension according to claim 8.

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