Linear actuator

Abstract

To relieve a load applied to a feed screw and to reduce torque applied to the feed screw when the feed screw is not rotated.SOLUTION: The linear-motion actuator includes a cylindrical linear-motion rod which is linearly reciprocated in accordance with rotation of the feed screw, a guide sleeve which guides the linear reciprocation of the linear-motion rod, an attachment section which is disposed on a side of the linear-motion rod opposite to the feed screw and which is attached to the structure, and an electromagnetic brake which locks the linear-motion rod to the attachment section. The electromagnetic brake locks the rectilinearly movable rod to the mounting section when the feed screw is rotated, and releases the lock of the rectilinearly movable rod to the mounting section when the feed screw is not rotated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a linear actuator. [Background technology]

[0002] Patent Document 1 discloses a linear motion actuator that includes a feed screw that can be rotated and a linear motion member that moves linearly as the feed screw rotates. This linear motion actuator is provided with a rotating shaft of a motor that rotates the feed screw and an electromagnetic brake that brakes the feed screw. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-107942 Summary of the Invention [Problem to be solved by the invention]

[0004] A linear actuator with a lead screw is sometimes used as a full active suspension or full active damper for vibration control of a structure. In this case, the rotation direction of the lead screw is switched, causing the linear member to move back and forth linearly in the opposite direction to the vibration applied to the structure.

[0005] A full-active damper receives loads from the structure not only when the motor is rotating the lead screw, but also when the motor is not rotating the lead screw (when the linear actuator is not operating). The load is transmitted from the linear member to the lead screw, for example, along the axial direction of the lead screw. Therefore, when the load is large, an impact is applied to the lead screw along the axial direction. Impacts in the axial direction may shorten the life of the lead screw and the parts that rotate the lead screw.

[0006] Furthermore, as the linear member moves in the axial direction, torque is applied to the feed screw, causing it to rotate. This torque is transmitted to the motor that rotates the feed screw. If there is a power transmission mechanism, such as a gear mechanism, between the motor and the feed screw, the torque is also applied to the power transmission mechanism. This may shorten the lifespan of the motor that rotates the feed screw and the power transmission mechanism.

[0007] Therefore, the present invention provides a linear actuator that alleviates the load applied to the feed screw and reduces the torque applied to the feed screw when the feed screw cannot be rotated. [Means for solving the problem]

[0008] One aspect of the present invention provides a linear actuator. The linear actuator includes a rotatable lead screw, a nut member that is caused to move reciprocally along the axial direction of the lead screw as the lead screw rotates, a cylindrical linear rod that is fixed to the nut member and moves reciprocally together with the nut member, a guide sleeve that has a cylindrical internal space into which the linear rod is inserted and that guides the reciprocating linear motion of the linear rod, a mounting part that is disposed on the opposite side of the lead screw from the linear rod and is attached to a structure, and an electromagnetic brake that locks the linear rod to the mounting part when the lead screw is rotated, thereby restricting the relative movement of the linear rod and the mounting part along the axial direction and restricting the relative rotation of the linear rod and the mounting part about the axial direction. When the lead screw is not rotated, the electromagnetic brake releases the lock of the linear rod from the mounting portion, allowing relative movement of the mounting portion and the linear rod along the axial direction and allowing relative rotation of the mounting portion and the linear rod around the axial direction. [Effects of the Invention]

[0009] In one aspect of the present invention, when the lead screw is rotated, the electromagnetic brake locks the linear-acting rod to the mounting portion. The locking restricts the mounting portion from moving relative to the linear-acting rod along the axial direction of the lead screw, thereby transmitting the motion of the linear-acting rod to the structure to be damped. Furthermore, the locking restricts the rotation of the linear-acting rod relative to the mounting portion, ensuring that the linear-acting rod moves linearly as the lead screw rotates. On the other hand, when the lead screw is prevented from rotating, the electromagnetic brake releases the lock on the linear-acting rod from the mounting portion. Releasing the lock allows the mounting portion to move relative to the linear-acting rod along the axial direction of the lead screw, thereby reducing the impact transmitted from the mounting portion to the linear-acting rod and then to the lead screw. Furthermore, the release of the lock allows the linear-acting rod to rotate relative to the mounting portion, so that when the linear-acting rod moves in the axial direction, the linear-acting rod rotates with almost no torque applied to the lead screw. In this way, when the feed screw cannot be rotated, the impact on the feed screw can be alleviated and the torque applied to the feed screw can be reduced, thereby extending the life of the feed screw and the parts that rotate the feed screw. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing a linear motion actuator according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the linear actuator in a retracted state. [Figure 3] FIG. 3 is a cross-sectional view showing the linear actuator in an extended state. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the electromagnetic brake in the linear actuator when it is unlocked. [Figure 5] FIG. 5 is an enlarged cross-sectional view of the electromagnetic brake when locked. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The drawings are not necessarily drawn to scale, and some features may be exaggerated or omitted.

[0012] As shown in Fig. 1, a linear motion actuator 1 according to an embodiment of the present invention has a gear transmission mechanism 2. The gear transmission mechanism 2 is driven by a motor 3. The motor 3 is, for example, a servo motor or a stepping motor.

[0013] The motor 3 has a rotating shaft 3a. The motor 3 is fixed to a bracket 6, and the rotating shaft 3a passes through a hole formed in an end wall 6a of the bracket 6. The bracket 6 is made of a rigid material such as metal or resin. The end wall 6a of the bracket 6 is fixed to a bottom wall 31a and a central wall 31b of a housing 31 of the linear motion actuator 1 with screws.

[0014] The gear transmission mechanism 2 is driven by a rotating shaft 3a of a motor 3. The gear transmission mechanism 2 has a first gear 7, a second gear 8, and a third gear 9. The first gear 7 is fixed to the rotating shaft 3a and rotates together with the rotating shaft 3a. For example, the first gear 7 is fixed to the rotating shaft 3a by a key 3b.

[0015] The second gear 8 meshes with the first gear 7 and is driven to rotate by the first gear 7. The second gear 8 is fixed to a rotating shaft 8a and rotates together with the rotating shaft 8a. For example, the second gear 8 is fixed to the rotating shaft 8a by a key 8b.

[0016] The rotating shaft 8a is rotatably supported by rolling bearings 10 and 11. The rolling bearing 10 is fixed to a central wall 31b of a housing 31 of the linear motion actuator 1, and the rolling bearing 11 is fixed to a cover 32.

[0017] The third gear 9 meshes with the second gear 8 and is driven to rotate by the second gear 8. The third gear 9 is fixed to a rotating shaft 9a and rotates together with the rotating shaft 9a. For example, the third gear 9 is fixed to the rotating shaft 9a by a key 9b.

[0018] In this embodiment, the rotary shaft 9a is the output shaft of the gear transmission mechanism 2, and the feed screw 34 of the linear motion actuator 1 is formed on an extension of the rotary shaft 9a.

[0019] The rotating shaft 9a is rotatably supported by rolling bearings 13 and 14. The rolling bearings 13 and 14 are supported by a bearing housing 15, which is fixed with screws to a central wall 31b and an upper wall 31c of a housing 31 of the linear motion actuator 1. The rolling bearings 13 and 14 are enclosed by the bearing housing 15 and a bearing cover 16. The bearing cover 16 is fixed to the bearing housing 15 with screws.

[0020] The linear motion actuator 1 includes the above-mentioned gear transmission mechanism 2, a housing 31, a cover 32, an end attachment portion 33, a feed screw 34, a nut member 35, a linear motion rod 36, an end attachment portion 37, and an electromagnetic brake 50.

[0021] The housing 31 is formed from a rigid material such as metal or resin, and has the lower wall 31a, central wall 31b, and upper wall 31c, as described above, as well as a cylindrical guide sleeve 38 that guides the linear motion of the linear motion rod 36. The guide sleeve 38 is integrally connected to the central wall 31b and the upper wall 31c. In this specification, the terms "lower wall 31a," "central wall 31b," and "upper wall 31c" are merely names used to facilitate understanding from the drawings, and are not intended to limit the orientation of the linear motion actuator 1 during use.

[0022] The cover 32 is made of a rigid material such as metal or resin and is fixed to the lower wall 31a and upper wall 31c of the housing 31 with screws, and together with the housing 31 and the bearing cover 16, defines a gear space 41 that surrounds the gear transmission mechanism 2. The cover 32 protects the spur gears 7, 8, 9 and other mechanical parts from foreign matter such as dust and water.

[0023] The end mounting portion 33 is integrally connected to the cover 32. A circular through hole 33a is formed in the end mounting portion 33. The through hole 33a is used to attach the end mounting portion 33 to a part 45 of a structure. For example, a bolt for attaching the end mounting portion 33 to the part 45 of a structure is inserted into the through hole 33a.

[0024] The lead screw 34 is a part of the rotating shaft 9a of the third gear 9. The lead screw 34 is arranged coaxially with the guide sleeve 38. The lead screw 34 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.

[0025] The nut member 35 engages with the feed screw 34. A portion of the nut member 35 (body portion 35b) is inserted into the internal space of the linear motion rod 36. The head portion 35a of the nut member 35 is not inserted into the linear motion rod 36, but is fixed to the linear motion rod 36 with a screw. The linear motion rod 36 is a cylindrical pipe made of a rigid material such as metal or resin. The linear motion rod 36 is arranged coaxially with the feed screw 34 and guide sleeve 38. The linear motion rod 36 is inserted into the cylindrical internal space of the guide sleeve 38 and is capable of reciprocating movement along the axial direction of the linear motion rod 36. The feed screw 34 is arranged in the cylindrical internal space of the linear motion rod 36.

[0026] As will be described later, the linear motion rod 36 is restricted from rotating relative to the guide sleeve 38. Therefore, when the feed screw 34 rotates, the nut member 35 engaged with the feed screw 34 and the linear motion rod 36 fixed to the nut member 35 are moved linearly along the axial direction of the feed screw 34.

[0027] 2 shows the retracted state of the linear motion actuator 1 (more precisely, the retracted state of the linear motion rod 36). In this manner, the feed screw 34, which is an extension of the rotary shaft 9a, is rotated by the gear transmission mechanism 2, and the nut member 35 and the linear motion rod 36 are moved linearly in accordance with the rotation of the feed screw 34. In the retracted state, the linear motion rod 36 is retracted into the guide sleeve 38.

[0028] If the gear transmission mechanism 2 is rotated in the reverse direction, the linear motion rod 36 is extended, as opposed to the state shown in Figure 2. Figure 3 shows the linear motion actuator 1 in an extended state (more precisely, the linear motion rod 36 in an extended state). In this way, as the feed screw 34 rotates, the nut member 35 and the linear motion rod 36 are caused to move back and forth linearly along the axial direction of the feed screw 34. In the extended state, the linear motion rod 36 extends from the guide sleeve 38.

[0029] The linear motion range (stroke) of the linear motion rod 36 is finite. Therefore, the motor 3 is controlled by a motor driver (not shown) so as to rotate within a finite angular range. In this way, the motor 3 is rotated within a finite angular range, and the gears 7, 8, and 9 of the gear transmission mechanism 2 also rotate within a limited angular range.

[0030] The linear motion rod 36, which is a cylindrical pipe, has an end wall 36a. An electromagnetic brake 50 is attached to the end wall 36a, and an end mounting portion (mounting portion) 37 is attached to the electromagnetic brake 50. Therefore, the end mounting portion 37 is located on the opposite side of the linear motion rod 36 from the feed screw 34.

[0031] As will be described later, the electromagnetic brake 50 locks and unlocks the linear rod 36 to the end mounting portion 37.

[0032] A circular through-hole 37a is formed in the end mounting portion 37. The through-hole 37a is used to attach the end mounting portion 37 to a portion 46 of a structure. For example, a bolt for attaching the end mounting portion 37 to the portion 46 of a structure is inserted into the through-hole 37a.

[0033] The end mounting portion 33 and the end mounting portion 37 are attached to a structure (not shown) in which the linear actuator 1 will be used. For example, the linear actuator 1 can be used as a fully active damper for lateral vibration control of a railway vehicle or other transportation equipment, or for lateral vibration control of a building. In this case, the lead screw 34, nut member 35, linear rod 36, and guide sleeve 38 are arranged with their longitudinal directions aligned horizontally. The end mounting portion 33 is attached to a portion 45 on one side of the structure (e.g., transportation equipment or a building), and the end mounting portion 37 is attached to a portion 46 on the other side of the structure.

[0034] Alternatively, the linear actuator 1 can be used as a fully active damper for vertical vibration control of transportation equipment or buildings. In this case, the linear actuator 1 is arranged in an orientation in which the end mounting portion 33 is positioned upward and the end mounting portion 37 is positioned downward. The end mounting portion 33 is attached to a portion 45 at the top of the structure, and the end mounting portion 37 is attached to a portion 46 at the bottom of the structure.

[0035] By attaching the end mounting portions 33, 37 to a structure, the linear motion rod 36 to which the end mounting portion 37 is connected is restricted from rotating relative to the guide sleeve 38. However, rotation of the linear motion rod 36 relative to the guide sleeve 38 is restricted only while the electromagnetic brake 50 locks the linear motion rod 36 to the end mounting portion 37. While the electromagnetic brake 50 releases the lock of the linear motion rod 36 from the end mounting portion 37, the linear motion rod 36 can rotate relative to both the end mounting portion 37 and the guide sleeve 38.

[0036] To facilitate the linear motion of the linear motion rod 36, a plain bearing 42 and a plain bearing 43 are interposed between the outer peripheral surface of the linear motion rod 36 and the inner peripheral surface of the guide sleeve 38. The plain bearings 42 and 43 are, for example, cylindrical bushings. However, each of the plain bearings 42 and 43 may also be a split plain bearing having multiple arc-shaped pieces.

[0037] The plain bearing 42 is disposed in a circumferential groove formed in the inner peripheral surface of the guide sleeve 38 and is stationary relative to the guide sleeve 38. The inner peripheral surface of the plain bearing 42 is in slidable contact with the outer peripheral surface of the linear motion rod 36.

[0038] The plain bearing 43 is disposed in a circumferential groove formed in the outer circumferential surface of the linear motion rod 36 and is stationary relative to the linear motion rod 36. The outer circumferential surface of the plain bearing 43 is in slidable contact with the inner circumferential surface of the guide sleeve 38.

[0039] Although not absolutely necessary, a stopper 40 is fixed to the end of the lead screw 34 with a screw. The stopper 40 limits the range of linear movement of the linear acting rod 26. When the linear acting rod 36 extends from the guide sleeve 38 further than the state shown in FIG. 3 and reaches its maximum extension, the stopper 40 comes into contact with the nut member 35, preventing the nut member 35 from moving and thus preventing further extension of the linear acting rod 36. When the linear acting rod 36 retracts into the guide sleeve 38 further than the state shown in FIG. 2 and reaches its maximum retraction, the stopper 40 comes into contact with the end wall 36a of the linear acting rod 36 and prevents further retraction of the linear acting rod 36.

[0040] 4 and 5, the electromagnetic brake 50 will be described in detail. The electromagnetic brake 50 includes a brake housing 51, a permanent magnet 52, a coil 53, a sliding bearing 54, an armature 55, a pressing member 56, a spring 57, a lining plate 58, a cable support ring 59, rolling bearings 60 and 61, a bearing spacer 62, an insulating ring 63, slip rings 64 and 65, and brushes 66 and 67.

[0041] The brake housing 51 is an iron cylinder, and is fixed to the end wall 36a of the linear motion rod 36 by a plurality of screws 70. The brake housing 51 is the stator or yoke of the electromagnetic brake 50. The brake housing 51 has an annular space 51a, in which a permanent magnet 52 and a coil 53 are arranged.

[0042] The brake housing 51 has a central hole 51b in which a sliding bearing 54 is attached. The sliding bearing 54 is, for example, a cylindrical bushing. However, the sliding bearing 54 may also be a split sliding bearing having multiple arc-shaped pieces.

[0043] The end mounting portion 37 has a ring portion having a through hole 37a and a shaft portion 37b that is integrally connected to the ring portion and has a central axis 37c. The shaft portion 37b is inserted into a plain bearing 54. When the end mounting portion 37 and the linear motion rod 36 are not locked together, the end mounting portion 37 can rotate around the central axis 37c. In other words, the plain bearing 54 supports the end mounting portion 37 rotatably.

[0044] The brake housing 51 has a cylindrical space 51c that communicates with the space 51a and the central hole 51b. An armature 55 and a pressing member 56 are disposed in the space 51c.

[0045] The pressing member 56 is a disk made of a rigid material such as metal or resin, and is fixed to the shaft portion 37b of the end mounting portion 37 by a screw 72.

[0046] The armature 55 is an iron ring that is disposed around the sliding bearing 54. The armature 55 is movable relative to the brake housing 51 and the pressing member 56 along the central axis 37c of the end mounting portion 37.

[0047] A permanent magnet 52 fixed to the brake housing 51 generates a magnetic field that acts on the armature 55. That is, the permanent magnet 52 attracts the armature 55 to the right in the figure. The brake housing 51 acts as a yoke to strengthen the magnetic field. Furthermore, a coil 53 fixed to the brake housing 51 generates a magnetic force that cancels out the magnetic force of the permanent magnet 52 when current is applied.

[0048] A pin 74 is attached to the brake housing 51. The pin 74 prevents the armature 55 from rotating around the central axis 37c, and guides the armature 55 as it moves along the central axis 37c.

[0049] A spring 57 is provided in the brake housing 51. The spring 57 constantly applies a force to the armature 55 that presses the armature 55 toward the linear acting rod 36 (to the left in the figure). When the force of the spring 57 is greater than the force that pulls the armature 55 toward the right in the figure, the spring 57 moves the armature 55 toward the linear acting rod 36, and the armature 55 presses the pressing member 56 toward the linear acting rod 36.

[0050] An annular lining plate 58 is fixed to the end wall 36a of the linear motion rod 36. When the armature 55 presses the pressing member 56 toward the linear motion rod 36, the pressing member 56 is pressed against the lining plate 58. This locks the linear motion rod 36 to the end mounting portion 37.

[0051] A cable support ring 59 is disposed around the brake housing 51. A cable 76 that supplies power to the coil 53 of the electromagnetic brake 50 is attached to the cable support ring 59.

[0052] To allow relative rotation between the cable support ring 59 and the brake housing 51, two rolling bearings 60, 61 are arranged between the cable support ring 59 and the brake housing 51. A bearing spacer 62 is interposed between the rolling bearings 60, 61. The bearing spacer 62 has an outer ring and an inner ring made of metal, and an insulating ring 63 made of an electrical insulator is arranged between the outer ring and the inner ring.

[0053] Leads 53a and 53b of coil 53 pass radially through brake housing 51, and then pass through the inner ring of bearing spacer 62 and insulating ring 63, and are electrically connected to slip rings 64 and 65, respectively. Slip rings 64 and 65 are endless rings made of a conductive material, and are arranged coaxially with insulating ring 63 on the outer peripheral surface of insulating ring 63 that surrounds brake housing 51. Insulating ring 63 electrically insulates slip rings 64 and 65.

[0054] The wires 76a and 76b of the cable 76 are passed radially from the outer peripheral surface to the inner peripheral surface of the cable support ring 59 and further passed through the outer ring of the bearing spacer 62. In the bearing spacer 62, the wires 76a and 76b are electrically insulated from the bearing spacer 62 by insulating sheaths 76c and 76d. Between the outer ring and the inner ring of the bearing spacer 62, the wires 76a and 76b are electrically connected to conductive brushes 66 and 67, respectively. In this manner, the wires 76a and 76b of the cable 76 and the brushes 66 and 67 are attached to the cable support ring 59, which is rotatably disposed in the brake housing 51. The brushes 66 and 67 rotate relative to the slip rings 64 and 65 and supply power to the coil 53 by slidably contacting the slip rings 64 and 65.

[0055] 1 to 3, the linear motion actuator 1 has a control unit 80 that controls the motor 3 that drives the feed screw 34 and the electromagnetic brake 50. The control unit 80 controls the supply and cut-off of current to the motor 3 and the coil 53 of the electromagnetic brake 50.

[0056] The electromagnetic brake 50 is of a positive action type, and when current is applied to the coil 53, it locks the linear motion rod 36 to the end mounting portion 37, and when current is cut off to the coil 53, it releases the lock. When the control unit 80 applies current to the motor 3 to rotate the motor 3, it applies current to the coil 53 of the electromagnetic brake 50, causing the electromagnetic brake 50 to lock the linear motion rod 36 to the end mounting portion 37. Therefore, when the feed screw 34 is rotated and the nut member 35 and the linear motion rod 36 are caused to move linearly, the electromagnetic brake 50 locks the linear motion rod 36 to the end mounting portion 37.

[0057] On the other hand, when the motor 3 is not energized, the control unit 80 does not energize the coil 53 of the electromagnetic brake 50, thereby releasing the lock. Therefore, when the feed screw 34 is not rotated and the nut member 35 and the linear motion rod 36 are not moved linearly, the electromagnetic brake 50 releases the lock of the linear motion rod 36 from the end attachment portion 37.

[0058] The state of the electromagnetic brake 50 when unlocked will be described with reference to Figure 4. At this time, no current is applied to the coil 53. In this state, the magnetic force generated by the permanent magnet 52 overcomes the force of the spring 57, compressing the spring 57 and attracting the armature 55 to the right in the figure. As a result, the armature 55 moves away from the pressing member 56 fixed to the end mounting portion 37, and the force pressing the pressing member 56 against the lining plate 58 fixed to the nut member 35 is lost.

[0059] Therefore, the lock of the linear rod 36 relative to the end mounting portion 37 is released, allowing relative movement of the end mounting portion 37 and the linear rod 36 along the axial direction of the feed screw 34, and allowing relative rotation of the end mounting portion 37 and the linear rod 36 around the axial direction of the feed screw 34.

[0060] The state of the electromagnetic brake 50 when locked will be described with reference to Figure 5. At this time, current is applied to the coil 53, and the magnetic force generated by the coil 53 cancels out the magnetic force caused by the permanent magnet 52. The spring 57 then moves the armature 55 toward the linear motion rod 36, and the armature 55 presses the pressing member 56 toward the linear motion rod 36. In this way, the pressing member 56 fixed to the end mounting portion 37 is pressed against the lining plate 58 fixed to the nut member 35.

[0061] Therefore, the linear rod 36 is locked relative to the end mounting portion 37, and the relative movement between the end mounting portion 37 and the linear rod 36 along the axial direction of the feed screw 34 is restricted, i.e., stopped, and the relative rotation between the end mounting portion 37 and the linear rod 36 around the axial line of the feed screw 34 is restricted, i.e., stopped.

[0062] As described above, in this embodiment, when the feed screw 34 is rotated to cause the nut member 35 and the linear motion rod 36 to move linearly, the electromagnetic brake 50 locks the end mounting portion 37 to the linear motion rod 36. The locking restricts the end mounting portion 37 from moving relative to the linear motion rod 36 along the axial direction of the feed screw 34, and the motion of the linear motion rod 36 is transmitted to the structure that is the target of vibration damping. In addition, because the locking restricts the rotation of the linear motion rod 36 relative to the end mounting portion 37, the linear motion of the linear motion rod 36 is reliably caused to move linearly as the feed screw 34 rotates.

[0063] On the other hand, when the feed screw 34 is not rotated and the nut member 35 and the linear motion rod 36 are not moved linearly, the electromagnetic brake 50 releases the lock of the linear motion rod 36 from the end attachment portion 37. By releasing the lock, the end attachment portion 37 becomes capable of moving relative to the linear motion rod 36 along the axial direction of the feed screw 34, and the shock transmitted from the end attachment portion 37 to the linear motion rod 36 and further to the feed screw 34 is alleviated.

[0064] Furthermore, releasing the lock allows the linear acting rod 36 to rotate relative to the end mounting portion 37. The plain bearing 54 attached to the brake housing 51 rotatably supports the end mounting portion 37 relative to the linear acting rod 36 (in other words, the plain bearing 54 allows the linear acting rod 36 to rotate relative to the end mounting portion 37). Therefore, when the linear acting rod 36 moves in the axial direction, the linear acting rod 36 rotates with almost no torque applied to the lead screw 34. In this way, when the lead screw 34 cannot be rotated, the impact applied to the lead screw 34 can be mitigated and the torque applied to the lead screw 34 can be reduced, thereby extending the life of the lead screw 34 and the parts that rotate the lead screw 34.

[0065] In the above embodiment, the electromagnetic brake 50 is of a direct action type, and when the control unit 80 energizes the motor 3 to rotate the motor 3, it energizes the coil 53 of the electromagnetic brake 50, causing the electromagnetic brake 50 to lock the linear acting rod 36 to the end mounting portion 37. When the control unit 80 does not energize the motor 3, it does not energize the electromagnetic brake 50. Therefore, the circuit (not shown) that supplies power to the motor 3 and the electromagnetic brake 50 can be simplified, for example, by using a series circuit.

[0066] However, the electromagnetic brake 50 may be of a reverse action type that locks the linear acting rod 36 to the end mounting portion 37 when the supply of current to the coil 53 is stopped and unlocks the linear acting rod 36 when the coil 53 is turned on. In this case, when the motor 3 is energized to rotate the motor 3, the control unit 80 stops the supply of current to the coil 53 of the electromagnetic brake 50 to lock the linear acting rod 36 to the end mounting portion 37 with the electromagnetic brake 50, and when the supply of current to the motor 3 is stopped to stop the rotation of the motor 3, the control unit 80 energizes the coil 53 of the electromagnetic brake 50 to release the lock caused by the electromagnetic brake 50.

[0067] 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 included within the scope of the invention.

[0068] For example, in the above embodiment, the gear transmission mechanism 2 has three gears 7, 8, and 9, but the number of gears provided in the gear transmission mechanism may be two, or four or more. Also, instead of the gear transmission mechanism 2, a belt mechanism or a chain mechanism may be used to rotate the feed screw 34, or the feed screw 34 may be directly rotated by a motor. [Explanation of symbols]

[0069] 1...linear actuator, 2...gear transmission mechanism, 3...motor, 3a...rotating shaft, 3b...key, 6...bracket, 6a...end wall, 7...first gear, 8...second gear, 8a...rotating shaft, 8b...key, 9...third gear, 9a...rotating shaft, 9b...key, 10, 11, 13, 14...rolling bearing, 15...bearing housing, 16...bearing cover, 31...housing, 31a...lower wall, 31b...central wall, 31c...upper wall, 32...cover, 33...end mounting portion, 33a...through hole, 34...feed screw, 35...nut member, 35a...head, 35b...body portion, 36...linear rod, 36a...end wall, 37...end mounting portion (mounting portion), 37a...through hole, 37b...shaft portion, 37c... Central axis, 38... guide sleeve, 40... stopper, 41... gear space, 42, 43... sliding bearing, 45, 46... structural part, 50... electromagnetic brake, 51... brake housing, 51a... space, 51b... central hole, 51c... space, 52... permanent magnet, 53... coil, 53a, 53b... reed, 57... spring, 55... armature, 54... sliding bearing, 56... pressing member, 58... lining plate, 59... cable support ring, 60, 61... rolling bearing, 62... bearing spacer, 63... insulating ring, 64, 65... slip ring, 66, 67... brush, 72... screw, 74... pin, 76... cable, 76a, 76b... wire, 76c, 76d... insulating sheath, 80... control part

Claims

1. a feed screw that can be rotated; a nut member that is caused to undergo a reciprocating linear motion along the axial direction of the feed screw in association with the rotation of the feed screw; a cylindrical linear motion rod fixed to the nut member and adapted to move in a linear reciprocating motion together with the nut member; a guide sleeve having a cylindrical internal space into which the linear motion rod is inserted and guiding the linear motion of the linear motion rod; a mounting portion that is disposed on the opposite side of the linear motion rod from the feed screw and that is attached to a structure; an electromagnetic brake that locks the linear motion rod to the mounting portion; Equipped with The electromagnetic brake is When the feed screw is rotated, the linear motion rod is locked to the mounting portion to restrict the relative movement of the mounting portion and the linear motion rod along the axial direction and restrict the relative rotation of the mounting portion and the linear motion rod around the axial direction; When the lead screw is not rotated, the lock of the linear-acting rod relative to the mounting portion is released to allow relative movement of the mounting portion and the linear-acting rod along the direction of the axis and relative rotation of the mounting portion and the linear-acting rod around the axis. A linear actuator characterized by:

2. The electromagnetic brake is a brake housing fixed to the linear motion rod; a bearing attached to the brake housing and rotatably supporting the attachment portion; an armature movable relative to the brake housing; a coil fixed to the brake housing to form a magnetic field acting on the armature; a flange member fixed to the mounting portion and pressed toward the linear motion rod by the armature; a slip ring disposed around the brake housing and electrically connected to the coil; a brush that is rotatably disposed relative to the brake housing, that is in slidable contact with the slip ring, and that supplies power to the coil; 2. The linear actuator according to claim 1, further comprising:

3. a motor that drives the feed screw; a control unit for controlling the motor and the electromagnetic brake; The control unit causes the electromagnetic brake to lock the linear motion rod to the mounting portion when the motor is driven, and causes the electromagnetic brake to release the lock when the motor is not driven.

3. The linear actuator according to claim 1 or 2.

4. The electromagnetic brake is of a positive action type, The control unit, when energizing the motor, energizes the electromagnetic brake to lock the linear motion rod to the mounting portion with the electromagnetic brake, and, when de-energizing the motor, does not energize the electromagnetic brake to release the lock.

4. The linear actuator according to claim 3.

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