JP2007154955A - Direct-acting actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a direct-acting actuator axially, and miniaturize the whole direct-acting actuator. <P>SOLUTION: The direct-acting actuator 10 comprises a circular spline 28 having a screw groove 40 in the inner peripheral surface, a flexible spline 26 disposed in the circular spline 28 having a screw thread 38 in the outer peripheral surface, a pulse generator 20 partially engaged with the circular spline 28 by deflecting the flexible spline non-circularly, a harmonic drive gearing formed to cause the axial displacement of the circular spline by relative rotation of the screw thread 38 and the screw groove 40 with the circular spline 28 and the flexibile spline 26, a motor 12 to rotate and drive the pulse generator 20, and an output shaft 32 connected to one end of the circular spline 28, and coaxially retained with the circular spline 28 axially and slidably. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an actuator including a wave gear device having a circular spline, a flex spline, and a wave generator.

A wave gear device including a circular spline, a flex spline, and a wave generator that flexes the flex spline into a non-circular shape and partially meshes with the circular spline is used to obtain a large reduction ratio. For example, in Patent Document 1, teeth and screw grooves are provided on the outer peripheral surface of a flexspline and the inner peripheral surface of a fixed circular spline, and the flexspline is moved in the axial direction by operating rotation of two wave generators. And the technique to displace to the circumferential direction is disclosed. This technique can be said to be useful in that it can obtain a significantly reduced circumferential movement and an axial movement, and can also be used for a linear actuator.
Japanese Utility Model Publication No. 6-38195

  In the technique of Patent Document 1, the output shaft is connected to the flexspline. In order to maintain the output shaft in a stable state, the output shaft must be supported at at least two points. However, since the flexspline has low rigidity and a support point cannot be provided on the flexspline, a rigid output shaft is required. It is necessary to provide support points in at least two locations. At this time, it is also necessary to secure a certain distance between these support points from the viewpoint of stability of the output shaft. Therefore, the output shaft of the linear actuator designed under these needs is long in the axial direction. Furthermore, considering that the stroke for the output shaft to move in the axial direction is secured between the flexspline and the circular spline, the linear actuator as a whole becomes longer in the axial direction. As a result, the installation location of the linear actuator is limited due to space problems.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to reduce the size of the entire linear motion actuator by shortening the linear motion actuator in the axial direction.

  One embodiment of the present invention relates to a linear motion actuator. This linear actuator includes a circular spline having a thread groove on the inner peripheral surface, a flex spline having a thread on the outer peripheral surface disposed inside the circular spline, and flexing the flex spline into a non-circular shape. A wave gear device that includes a wave generator that meshes with each other, and has a thread groove and a thread formed so that axial displacement of the circular spline is generated by relative rotation of the circular spline and flexspline, and the wave generator is rotated A motor to be driven and an output shaft coupled to one end of the circular spline and held so as to be slidable in the axial direction coaxially with the circular spline.

  In this aspect, the output shaft is coupled to a rigid circular spline. Therefore, it is possible to provide a support point at one point on the circular spline and one point on the output shaft having the same rigidity, and to support the output shaft and the circular spline coupled thereto at these two points. Thus, the axial length of the linear actuator can be shortened as much as the number of support points on the output shaft is one while securing the distance of the support points to some extent and maintaining the stable state of the output shaft. Further, a sufficient stroke allowance for the output shaft to move in the axial direction can be secured.

  The linear motion actuator may further include a rotation restricting member that is provided on at least a part of the outer periphery of the circular spline and that allows movement in the axial direction while restricting the rotation of the circular spline. According to this aspect, even if the wave generator rotates and the position where the flex spline and the circular spline mesh with each other moves in the circumferential direction, the rotation of the circular spline is restricted by the rotation support member. As a result, the circular spline can be moved in the axial direction without rotating.

  The linear motion actuator may further include a strain gauge that is attached to the surface of the flexspline and detects the flexspline strain. Accordingly, the strain is detected by the strain gauge of the flexspline, and when the strain is detected, a process for reducing the strain can be executed to avoid ratcheting.

The linear motion actuator may further include a stopper that rotates together with the wave generator and restricts a deflection of a predetermined amount or more in the inner diameter direction of the flexspline. When a load is applied to the flexspline in the axial direction, the flexspline has low rigidity, so that it bends not only in the axial direction but also in the inner diameter direction. As a result, there is a possibility that the meshing of the screw grooves in the flexspline and the circular spline is disengaged and ratcheting occurs. Therefore, a stopper that restricts the flexure line from bending in the inner diameter direction is provided. As a result, when the flexspline is bent by a predetermined amount or more in the inner diameter direction, the inner peripheral surface of the flexspline comes into contact with the stopper, so that the flexspline can be prevented from further bending in the inner diameter direction. As a result, it is possible to suppress the thread groove from being removed and to avoid ratcheting. Further, the stopper does not come into contact with the inner peripheral surface of the flexspline unless the flexspline is bent in the inner diameter direction.

  According to the vehicle braking device of the present invention, it is possible to reduce the size of the linear actuator.

In the present embodiment, first, problems in the conventional linear actuator will be described, and then the linear actuator in which the problems have been solved in the first embodiment and the second embodiment will be described.
FIG. 6 is an axial sectional view of a conventional linear actuator. The linear actuator 210 is an actuator for taking out the rotation of the motor 212 as an output in the axial direction of the output shaft 232. In the linear actuator 210, a motor 212 and a wave generator 220 are integrated. The motor 212 is configured so that the rotor 216 surrounds the stator 218 attached to the center shaft 214 in the circumferential direction.

The wave generator 220 includes an elliptical wave core 222 and a bearing 224. The wave core 222 bends and deforms the flex spline 226 into an elliptical shape via the bearing 224. A thread 238 is formed on the outer peripheral surface of the flexspline 226, and a thread groove 240 that meshes with the thread 238 is formed on the inner peripheral surface of the circular spline 228. The thread 238 of the flex spline 226 deformed into an elliptical shape meshes with the thread groove 240 at two points on the elliptical long axis. A rotor 216 is attached to the inside of the wave core 222. When the motor 212 is driven to rotate, the rotor 216 rotates and the wave core 222 rotates. When the wave core 222 rotates, the meshing position of the thread 238 and the thread groove 240 moves in the circumferential direction. Due to the movement of the meshing position, the flex spline 226 moves in the axial direction by the action of the screw thread 238 and the screw groove 240. An output shaft 232 is coupled to one end of the flexspline 226. As the flexspline 226 moves, the output shaft 232 also moves in the axial direction. The circular spline 228 is fixed, does not rotate in the circumferential direction, and does not move in the axial direction.
A linear actuator that moves the output shaft in the axial direction is known.

  In order to support the output shaft 232 in a stable state, it is necessary to support at least two points. In the linear actuator 210, an output shaft 232 is coupled to a flex spline 226 having low rigidity. Here, since the flex spline 226 has low rigidity, the flex spline 226 cannot be provided with a support point. For this reason, in order to keep the output shaft 232 in a stable state, as shown in FIG. 6, two bushes, a bush 234 and a bush 236, must be attached to the output shaft 232 to support the output shaft 232. A sufficient distance is secured between the bush 234 and the bush 236 to stabilize the output shaft 232. Hereinafter, the axial distance between two support points is also referred to as an “output shaft support span”. In FIG. 6, the interval between the bush 234 and the bush 236 is shown as an output shaft support span.

Further, in the linear actuator 210, as shown in FIG. 6, it is necessary to secure a distance that the flex spline 226 can move in the axial direction, that is, a stroke margin to some extent. When the output shaft 232 is coupled to the flex spline 226 as in the conventional linear actuator 210, the output shaft support span and stroke margin are positioned in series as shown in FIG. It becomes longer in the direction. Thereby, the problem that the location which can attach the linear actuator 210 was restrict | limited from the viewpoint of the space had arisen.
Further, in the linear actuator 210, since the output shaft 232 is coupled to the flexspline 226, the wave generator 220 needs to move in the axial direction together with the flexspline 226 while transmitting the rotation of the motor. There has also been a problem that the structure of the actuator 210 is complicated.
Hereinafter, in the first embodiment and the second embodiment, a linear actuator that solves the above-described problems of the conventional linear actuator will be described.

(First embodiment)
FIG. 1 is a cross-sectional view in the axial direction of the linear actuator 10 according to the first embodiment. The linear actuator 10 is an actuator for taking out the rotation of the motor 12 as a drive source as an output in the axial direction of the output shaft 32. The linear actuator 10 includes a circular spline 28, a flex spline 26, and a wave generator 20 that flexes the flex spline 26 into an elliptical shape and partially meshes with the circular spline 28. Here, the circular spline 28, the flex spline 26 and the wave generator 20 constitute a wave gear device. In this embodiment, the wave generator 20 bends the flexspline 26 into an elliptical shape. Alternatively, the wave generator 20 may bend the flexspline 26 into a substantially triangular shape. Good.

  The motor 12 includes a rotating shaft 14, a rotor 16, and a stator 18. In the motor 12, a rotor 16 is attached around the rotation shaft 14, and a stator 18 is disposed so as to surround the rotor 16 in the circumferential direction. The rotor 16 is rotated by the magnetic action between the rotor 16 and the stator 18, and the rotation can be extracted from the rotating shaft 14 as an output. The motor 12 is driven by a power source (not shown).

  The wave generator 20 includes a wave core 22 and a bearing 24, and a flexible bearing 24 is fitted to the outer periphery of the elliptical wave core 22. The wave core 22 deflects the flex spline 26 having low rigidity into an elliptical shape via the bearing 24. The rotating shaft 14 of the motor 12 is coaxially connected to the wave core 22, and the wave generator 20 rotates together with the rotating shaft 14.

  A thread 38 is formed on a part of the outer peripheral surface of the flex spline 26, and a thread groove 40 that meshes with the thread 38 is formed on a part of the inner peripheral surface of the circular spline 28. Here, the screw thread 38 and the screw groove 40 have different twist angles. The thread 38 of the flex spline 26 deformed into an elliptical shape meshes with the thread groove 40 at two points on the major axis of the ellipse. When the wave generator 20 rotates, the meshing position moves in the circumferential direction. Specifically, for example, when the wave generator 20 rotates counterclockwise when viewed from the motor 12, the meshing position moves in the clockwise direction. When the meshing position is moved due to the rotation of the rotating shaft 14, the flexspline 26 and the circular spline 28 are rotated relative to each other, and the circular spline 28 is rotated by the action of the screw thread 38 and the screw groove 40 having different torsion angles. Move in the direction. At this time, as will be described later, since the rotation of the circular spline 28 is restricted, the circular spline 28 does not rotate. The flex spline 26 is fixed so as not to move in the axial direction.

  As shown in FIG. 1, the linear actuator 10 is formed by covering a motor 12 as a driving source, a wave gear device, and an output shaft 32 with a housing 30. The circular spline 28 has a cylindrical shape, and one side is closed with a top plate. The output shaft 32 is coupled to the top plate of the circular spline 28 and is held coaxially with the circular spline 28 so as to be slidable in the axial direction. As a result, the output shaft 32 moves in the axial direction together with the circular spline 28. The stroke allowance shown in FIG. 1 is a distance that can move in the axial direction of the circular spline 28 and the output shaft 32.

  Here, the circular spline 28 and the output shaft 32 are supported by a bush 34 and a bush 36 on the outer periphery thereof. Here, a sufficient output support span is secured between the bush 34 and the bush 36 to stabilize the output shaft 32. In FIG. 1, the interval between the bush 34 and the bush 36 is shown as an output shaft support span. The circular spline 28 and the output shaft 32 are formed with a thickness and a thickness so as to have high rigidity.

  The bush 34 and the bush 36 restrict circumferential rotation while allowing the circular spline 28 and the output shaft 32 to move in the axial direction. In other words, when the meshing position of the screw thread 38 and the screw groove 40 moves in the circumferential direction, the circular spline 28 also has a force that rotates in the circumferential direction together with the axial force described above. Since it is regulated, the circular spline 28 and the output shaft 32 do not rotate.

  A plurality of strain gauges 42 are attached to the outer peripheral surface of the flexspline 26. FIG. 1 shows only one strain gauge 42 for convenience of explanation. As will be described later, the strain gauge 42 detects the strain of the flex spline 26 caused by the load applied in the axial direction with respect to the flex spline 26 as a change in resistance value.

  An elliptical disc-shaped stopper 46 that rotates together with the wave generator 20 is disposed on the same axis as the wave generator 20. The stopper 46 has an outer periphery smaller than the outer periphery of the wave generator 20, and a gap is provided between the flex spline 26 and the stopper 46 as shown in FIG. 1. As described later with reference to FIG. 2, the stopper 46 plays a role of suppressing the occurrence of ratcheting by suppressing the flexure line 26 from bending in the inner diameter direction. Here, the shape of the stopper 46 is an elliptical disc shape, but the shape of the stopper 46 is not limited to this. For example, the stopper 46 is arranged on the major axis of the elliptical wave generator 20 and is slightly shorter than the major axis. A rectangular shape having a thickness may be used. That is, the shape of the stopper 46 may be any shape that can suppress the bending of the flexspline 26 in the inner diameter direction in the major axis direction.

FIG. 2 is an enlarged view of a part of FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. Here, avoidance of ratcheting will be described with reference to FIG.
First, the cause of ratcheting will be described. It is assumed that an excessive load is applied to the circular spline 28 in the direction of arrow A via the output shaft 32. Then, the respective surfaces of the screw groove 40 and the screw thread 38 come into contact with each other, and the load in the direction of the arrow A is also applied to the flexspline 26 via the screw thread 38 and the screw groove 40, and the flexspline 26 is distorted in the axial direction.
Further, as shown in FIG. 2, the surfaces of the screw threads 38 and the screw grooves 40 are formed so as to be inclined with respect to the outer peripheral surfaces of the flexspline 26 and the circular spline 28. Therefore, a load is applied to the flex spline 26 in the direction of the inner diameter, that is, in the direction of arrow B. When a load is applied in the axial direction of the circular spline 28, the flex spline 26 is also bent in the direction of arrow B. Since the flex spline 26 has low rigidity, its flexure is relatively large. Ratcheting occurs when the thread 38 and the thread groove 40 are disengaged due to axial distortion and inner diameter deflection.

As shown in FIG. 2, there is a slight gap between the stopper 46 and the flexspline 26. Here, when the flexspline 26 is bent to some extent in the direction of the arrow B, the flexspline 26 comes into contact with the stopper 46 and is not further bent. If the stopper 46 is disposed so that the gap between the stopper 46 and the flexspline 26 is such that the engagement between the screw thread 38 and the screw groove 40 is not disengaged, the screw thread 38 and thread Since the engagement of the grooves 40 does not come off, the occurrence of ratcheting can be avoided. For example, ratcheting can be avoided by setting the gap interval smaller than the height of the screw thread 38 and the depth of the screw groove 40.
Further, by providing a gap between the stopper 46 and the flexspline 26, the stopper does not contact the inner peripheral surface of the flexspline unless the flexspline is bent in the inner diameter direction.

The strain gauge 42 affixed to the outer peripheral surface of the flex spline 26 detects the amount of strain in the axial direction of the flex spline 26 as a change in resistance value. It is determined whether or not ratcheting occurs based on the detected amount of distortion, and when it is determined that ratcheting occurs, control for avoiding ratcheting can be executed. This control will be described later with reference to FIGS.
In this embodiment, the strain gauge 42 is affixed to the outer peripheral surface of the flex spline 26. However, the position of the strain gauge 42 is not limited to this, and may be the surface of the flex spline 26. That is, the position where the strain gauge 42 is attached may be a position where the strain of the flexspline 26 can be detected.

FIG. 3 is a control block diagram for explaining control for avoiding ratcheting using the strain gauge 42.
As described above, when the strain gauge 42 detects strain, a change in resistance value, which is the detection result, is input to the strain amplifier 50 via a lead wire not shown in FIGS. 1 and 2. The strain amplifier 50 includes a bridge circuit and a current amplifier, and outputs an output voltage corresponding to the detected change in resistance value. The control unit 52 uses the output voltage to calculate the axial load, and according to the calculated value, in order to avoid ratcheting, the axial load on the flex spline 26 is reduced so as to reduce the axial load of the motor 12. Control the rotation.

  The control unit 52 includes a load calculation unit 54, a threshold holding unit 56, a determination unit 58 and an operation unit 60. The load calculation unit 54 calculates the load applied in the axial direction of the flexspline 26 using the voltage value output from the strain amplifier 50. The threshold holding unit 56 holds two thresholds, a first threshold and a second threshold for determining the degree of load. The second threshold is larger than the first threshold. The first threshold value is a load value such that ratcheting can be avoided if the rotation of the motor 12 is stopped. The second threshold value is a load value not only to stop the rotation of the motor 12 but also to prevent ratcheting unless the motor 12 is reversed. The determination unit 58 compares the load value calculated by the load calculation unit 54 with each of the first threshold value and the second threshold value held in the threshold value holding unit 56, and determines whether to execute rotation control of the motor 12. If so, it is determined how to execute the control. The operation unit 60 controls the rotation of the motor 12 according to the determination result of the determination unit 58. An ECU (Electronic Control Unit) mounted on the vehicle functions as the control unit 52.

  FIG. 4 is a flowchart showing a process of rotation control of the motor 12 for avoiding ratcheting. When strain, that is, a change in resistance value is detected by the strain gauge 42 (S10), an output voltage corresponding to the change in resistance value is output by the strain amplifier 50 (S12). The load calculation unit 54 calculates the load applied in the axial direction of the flexspline 26 using the output voltage (S14). When the calculated load is greater than the first threshold value (Y in S16) and greater than the second threshold value (Y in S18), the operating unit 60 reverses the motor 12, that is, reverse to the direction in which the motor 12 has been rotated. And then stop (S20). When the load is larger than the first threshold value and smaller than the second threshold value (N in S18), the operating unit 60 stops the motor 12 without reversing (S22). On the other hand, when the load is smaller than the first threshold value (N in S16), the operating unit 60 does not stop or reverse the motor 12.

  According to the first embodiment, in each of the circular spline 28 and the output shaft 32 having relatively high rigidity, by providing the support points by the bush 34 and the bush 36, the output shaft sufficient for stabilizing the output shaft 32 is provided. The axial length of the entire linear actuator can be shortened while securing the support span. Specifically, as shown in FIG. 1, since the output support span and the stroke allowance can be secured at the overlapping positions, the output support span and the stroke allowance shown in FIG. Compared with the direct acting actuator 210, the axial length of the entire actuator is shortened, and downsizing can be realized. Further, at this time, a sufficient stroke allowance for the output shaft 32 to move in the axial direction can be secured.

  Further, in the structure in which the output shaft is coupled to the conventional flex spline, the wave generator needs to move in the axial direction together with the flex spline while transmitting the rotation of the motor. In the first embodiment, since the flex spline 26 does not move in the axial direction, the wave generator 20 does not move either. Thereby, the structure of the linear motion actuator 10 can be simplified. Furthermore, since the strain gauge 42 and the stopper 46 are provided, the occurrence of ratcheting can be suppressed as described above.

  The linear actuator 10 can be attached to, for example, a vehicle steering device or a suspension device. In this case, the toe angle can be controlled by adjusting the length of the steering rod by the linear motion actuator 10, or the camber angle can be controlled by adjusting the length of the upper arm by the linear motion actuator 10. The linear actuator 10 can also be used to adjust the vehicle height by changing the distance between the wheel and the vehicle body. As described above, since the linear actuator 10 is reduced in size in the axial direction, it can be easily mounted from the viewpoint of space as compared with the conventional linear actuator.

  In the first embodiment, the circular spline 28 and the bush 36 are supported by two bushes, but three or more bushes for supporting these may be provided. Also by this, the output shaft 32 can be stabilized.

(Second Embodiment)
FIG. 5 is a cross-sectional view in the axial direction of the linear actuator 110 according to the second embodiment. Also in the linear motion actuator 110, as in the first embodiment, the thread 138 and the thread groove 140 mesh at two points on the elliptical long axis, and when the meshing position moves in the circumferential direction, the circular spline 128 moves in the axial direction. And the output shaft 132 coupled to one end of the circular spline 128 also moves in the axial direction. Similar to the first embodiment, the circular spline 128 and the output shaft 132 are supported by the housing 130 via bushes 134 and bushes 136 provided on the outer circumferences thereof. At this time, the output support span and the stroke allowance overlap, and the overall length of the linear motion actuator is shortened compared to the linear motion actuator 210 shown in FIG. The point that the strain gauge 142 and the stopper 146 are provided is the same as in the first embodiment.

  The second embodiment is different from the first embodiment in that the motor 112 and the wave generator 120 are integrated. Further, in the second embodiment, the motor 12 in which the rotor 16 rotates inside the stator 18 is used in that the motor 112 is used so that the rotor 116 rotates in the circumferential direction of the stator 118 attached to the central shaft 114. This is different from the first embodiment.

  As shown in FIG. 5, the motor 112 is disposed inside the wave core 122 of the wave generator 120. Specifically, the rotor 116 is press-fitted inside the elliptical wave core 122. The thread 138 of the flex spline 126 deflected in an elliptical shape via the bearing 124 meshes with the thread groove 140 at two points on the major axis of the ellipse. When the wave core 122 rotates together with the rotor 116, the meshing position moves in the circumferential direction. As a result, the circular spline 128 and the output shaft 132 move in the axial direction.

A cylindrical cavity 152 is coaxially formed in the output shaft 132, and one end of the central shaft 114 enters the cavity 152. A plurality of rolling elements 150 made of steel are fitted between the central shaft 114 and the cavity 152 as shown in FIG. Accordingly, when the output shaft 132 moves linearly with respect to the central shaft 114, the inner peripheral surface of the output shaft 132 moves while being in contact with the central shaft 114 via the rolling elements 150, so that the output shaft 132 is moved smoothly. be able to. Further, since the center shaft 114 fitted with the heavy stator 118 is supported by both ends, the center shaft 114 can be stabilized.
A plurality of annular rolling paths may be formed on the outer periphery of the center shaft 114, and rolling elements that move in the rolling path may be fitted. Alternatively, a spiral groove such as a ball screw may be formed on the outer periphery of the central shaft 114 and the inner periphery of the output shaft 132, and the rolling elements may be disposed on the rolling path formed by these grooves. In this manner as well, smooth movement of the output shaft 132 and stability of the central shaft 114 can be realized.

  By integrating the motor 112 and the wave generator 120, the linear actuator can be further shortened in the axial direction by the width of the wave generator 20, compared to the linear actuator 10 of the first embodiment. Thus, further downsizing of the entire linear actuator can be realized. At this time, the output shaft support span and the stroke allowance for stabilizing the output shaft 32 can be sufficiently secured. Instead of press-fitting the rotor 116 inside the wave core 122, the rotor 116 itself may be formed in an elliptical shape, and the bearing 124 may be fitted on the outer periphery thereof.

  Also in the second embodiment, since the flex spline 126 does not move in the axial direction, the wave generator 120 does not move in the axial direction. Thereby, the structure of the linear motion actuator 110 can be simplified. Further, since the linear motion actuator 110 is provided with the strain gauge 142 and the stopper 146, ratcheting can be suppressed as in the first embodiment.

  In the second embodiment, the circular spline 128 and the output shaft 132 are supported by two bushes, but three or more bushes for supporting these may be provided. Also by this, the output shaft 132 can be stabilized.

It is sectional drawing of the axial direction of the linear motion actuator concerning 1st Embodiment. It is the figure which expanded a part of FIG. It is a control block diagram for demonstrating the control for avoiding ratcheting using a strain gauge. It is a flowchart which shows the process of the rotation control of the motor for avoiding ratcheting. It is sectional drawing of the axial direction of the linear motion actuator concerning 2nd Embodiment. It is sectional drawing of the axial direction of the conventional linear motion actuator.

Explanation of symbols

  10 Linear Actuator, 12 Motor, 14 Rotating Shaft, 16 Rotor, 18 Stator, 20 Wave Generator, 22 Wave Core, 24 Bearing, 26 Flex Spline, 28 Circular Spline, 30 Housing, 32 Output Shaft, 34 Bush, 36 Bush , 38 thread, 40 thread groove, 42 strain gauge, 46 stopper, 50 strain amplifier, 52 control unit, 54 load calculation unit, 56 threshold holding unit, 58 judgment unit, 60 actuating unit, 150 rolling element, 152 cavity.

Claims (4)

Circular spline having a thread groove on the inner peripheral surface, flex spline having a screw thread on the outer peripheral surface disposed inside the circular spline, and wave generation that partially flexes the flex spline into a circular spline A wave gear device in which the thread groove and the thread are formed so as to cause axial displacement of the circular spline by relative rotation of the circular spline and the flexspline;
A motor for rotationally driving the wave generator;
An output shaft coupled to one end of the circular spline and held axially slidable on the same axis as the circular spline;
A linear motion actuator comprising:   The linear motion actuator according to claim 1, further comprising a rotation restricting member that is provided on at least a part of an outer periphery of the circular spline, and that allows movement in an axial direction while restricting rotation of the circular spline.   The linear motion actuator according to claim 1, further comprising a strain gauge that is attached to a surface of the flexspline and detects strain of the flexspline.   The linear motion actuator according to any one of claims 1 to 3, further comprising a stopper that rotates together with the wave generator and restricts a deflection of a predetermined amount or more in the inner diameter direction of the flexspline.

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