Linear actuator

Abstract

To provide a linear motion actuator which has a simple structure, can perform reciprocation motion of a linear member and locking motion during a pause a drive unit, is power-saving and compact in size.SOLUTION: A linear actuator A comprises: a cylindrical ball holder 1a; one or more balls 3 held on a wall part of the ball holder 1a; a screw 2a having a screw groove 2b with which the balls 3 engage and being inserted in the ball holder 1a; a drive unit 7 for driving the ball holder 1a or the screw 2a for rotation around a rotation axis X; a housing H holding these components; and linear motion guide parts 5 provided on one of the ball holder 1a and the screw 2 that does not rotate, and on the housing H, the linear motion guide parts 5 thrust-moving a linear member 2. The screw groove 2b includes a first region having a first lead angle in which the screw 2a is reciprocally moved, and a second region having a second lead angle in which relative reciprocation movement is paused.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a linear actuator in which a linear member provided with a screw is arranged in an engaged state via balls inside, for example, a cylindrical rotating member, and the linear member is reciprocated by driving the rotating member.

Background Art

[0002] Conventionally, as such a linear actuator, for example, there is one shown in Patent Document 1 (see

[0006] ,

[0011] ,

[0034] to

[0037] and FIGS. 1 to 4).

[0003] This prior art rotates a ball screw nut 8 by an electric motor 4 and reciprocates a ball screw shaft 7, which is a linear member, via balls 9. A plurality of position holding portions are provided at multiple locations in the middle of the stroke of the ball screw shaft 7, and even when an axial external force acts on the ball screw shaft 7 while the drive of the electric motor 4 is stopped, the position along the reciprocating movement direction of the ball screw shaft 7 is held.

[0004] Specifically, a pin 7c protruding in the radial direction is provided at one end of the ball screw shaft 7, and this end is a cylindrical sleeve 5 fixed to the housing 2. A concave groove 5a having a plurality of stepped portions 5c and 5d formed therein is formed in the sleeve 5. Further, a torsion coil spring 12 is provided at the other end of the ball screw shaft 7, and the ball screw shaft 7 is always torsionally biased to one side.

[0005] One wall portion of the concave groove 5a is linear along the reciprocating movement direction, and stepped portions 5c and 5d having different heights are sequentially formed in a portion facing this. The width of the concave groove 5a is formed narrower on the inner side along the direction of the external force acting on the ball screw shaft 7.

[0006] Regardless of whether the ball screw nut 8 is driven to the left or right, the ball screw shaft 7 undergoes some rotational movement due to the effect of its helical shape. When the ball screw shaft 7 moves inward, it rotates so that the pin 7c contacts the straight wall of the groove 5a, and the ball screw shaft 7 moves linearly while maintaining its rotational phase. On the other hand, when the ball screw shaft 7 moves outward, it rotates slightly in the opposite direction so that the pin 7c contacts the stepped wall of the groove 5a, and as it moves linearly, the pin 7c moves step by step, step by step, down to step 5c and step 5d.

[0007] When the electric motor 4 is idle, the motor's position-holding force is lost, and if an external force is applied to the protruding end of the ball screw shaft 7, the ball screw nut 8 rotates via the ball, causing the ball screw shaft 7 to attempt to move inward. However, the rotational biasing force of the torsion coil spring 12 causes the ball screw shaft 7 to rotate slightly, and the pin 7c is pressed against the wall on the side with the stepped portions 5c and 5d, and pushed inward. Subsequently, when the pin 7c is pushed to the position of the stepped portion 5c or 5d, the two come into contact, preventing further pushing of the ball screw shaft 7.

[0008] In other words, in this conventional technology, one side of the groove that stops the rotation during the reciprocating movement of the ball screw shaft 7 is formed in a stepped shape, and the ball screw shaft 7 is constantly twisted and biased toward this stepped side, thereby providing a restricting section in the middle of the stroke of the ball screw shaft 7. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2017-57931 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, in the conventional technology described above, when the electric motor 4 starts to drive, the ball screw shaft 7 always rotates in either the left or right direction, causing the pin 7c to collide with the wall of the groove 5a. Furthermore, as the pin 7c descends the steps 5c and 5d in sequence, the rotational biasing force of the torsion coil spring 12 causes the pin 7c to forcefully collide with the wall of the lower step. As a result, large vibrations and noise are continuously generated.

[0011] Furthermore, the rotational motion that always occurs during the reciprocating movement of the ball screw shaft 7 becomes an obstacle when connecting the output shaft of the ball screw shaft 7 to the position-controlled object. To resolve this, a separate configuration is required, for example, by connecting the position-controlled object to the end of the ball screw shaft 7 via a freely rotating member or the like.

[0012] Furthermore, in the case of the ball screw shaft 7, since the output shaft and the position holding part are provided on both sides of the helical screw region, the ball screw shaft 7 becomes longer, and the size of the linear actuator increases.

[0013] Thus, conventional linear actuators have various issues that need to be addressed, and there has been a need for a linear actuator that has a simple configuration, allows for reciprocating motion of the linear member and locking operation when the drive unit is idle, and is power-efficient and compact. [Means for solving the problem]

[0014] (Feature composition) The characteristic configuration of the linear actuator according to the present invention is: A ball holder formed in a cylindrical shape, At least one ball is held rotatably on the wall of the ball holder, The screw has a screw groove on its outer surface into which the ball engages, and is inserted into the ball holder. A drive unit that rotates one of the ball holder and the screw (rotating member) around the axis of rotation, A housing provided with the ball holder, the screw, and the drive unit, The system comprises a linear motion guide extending from the ball holder and the screw (a component that is not rotationally driven, i.e., a linear motion component) to the housing, which moves the linear motion component by thrust, The screw groove comprises a first region having a first lead angle that causes the screw and the ball holder to reciprocate relative to each other along the axis of rotation when the drive unit is rotated, and a second region having a second lead angle that pauses the relative reciprocating movement regardless of the rotational drive.

[0015] (effect) Linear actuators use screws with balls. This reduces friction in each part of the drive unit during operation, resulting in a more efficient linear actuator.

[0016] Furthermore, the screw groove provided in the screw includes a first region having a first lead angle used for predetermined linear motion and a second region having a second lead angle for stopping the linear motion. In particular, by including the second region, the screw can self-lock when, for example, a reverse input is applied to the screw when the linear actuator is stopped at a predetermined position. With this configuration, linear reciprocating motion of the linear member and locking operation when the drive unit is idle are possible with a simple configuration, and a linear actuator with low power consumption and a small size can be obtained.

[0017] (Feature composition) In the linear actuator according to the present invention, the second region may be provided with a concave portion in which the direction of the lead angle with respect to the rotation axis is reversed.

[0018] (effect) By providing a concave portion in the second region, the ball's resting position relative to the concave portion becomes stable. Therefore, the control of the resting position of the drive unit is simplified, and a simple linear actuator can be constructed.

[0019] Also, when forming the second region at the end of the screw groove, since the ball stops at the bottom of the concave portion when the drive part is stationary, the collision of the ball against the end of the screw groove can be eliminated. Therefore, it is possible to prevent the generation of vibration and noise particularly when the drive part stops.

[0020] (Characteristic configuration) In the linear actuator according to the present invention, it is advantageous that a biasing member abuts against at least one of the ball holder and the screw so that the ball is pressed toward the bottom of the concave portion.

[0021] (Effect) By providing the biasing member, the position holding function of the ball in the second region is further enhanced. Also, when the drive part is driven, the ball rolls while always abutting against one wall portion of the screw groove. Therefore, it is difficult for play to occur between the ball holder and the screw, and a silent and high-quality linear actuator can be obtained.

[0022] (Characteristic configuration) In the linear actuator according to the present invention, it is advantageous that a cylindrical sleeve that abuts against the ball while holding the ball is externally inserted into the ball holder and is configured to be movable along the rotation axis of the sleeve with respect to the ball holder and to be rotatable around the rotation axis.

[0023] (Effect) By providing the sleeve, the ball can be reliably held at a predetermined position of the ball holder, and for example, play between the ball and the screw groove can be reduced.

[0024] Also, the sleeve can move parallel to and rotate with respect to the ball holder. Therefore, when the ball rotates due to contact with the screw groove, the sleeve also moves due to contact with this ball. For this reason, the rotational resistance of the ball is reduced and the drive of the screw becomes smooth, and the drive efficiency of the linear actuator can be further enhanced.

[0025] (Feature composition) In the linear actuator according to the present invention, a spiral second screw groove can be provided on the inner surface of the sleeve, which contacts the ball that rolls by contact with the screw and extends in the direction of the ball's rolling motion.

[0026] (effect) By providing a second screw groove in the sleeve, where the ball rolls, the relative position of the sleeve to the ball becomes more limited compared to a configuration without the second screw groove. This suppresses the movement of the sleeve due to inertia, for example, when a vehicle equipped with the linear actuator accelerates or decelerates. As a result, vibrations and noise caused by the sleeve colliding with the moving end point are prevented.

[0027] Furthermore, if the inner surface of the second screw groove is substantially cylindrical, it is possible to bring the ball into line contact with the inner surface of the second screw groove, thereby reducing stress concentration on the surface of the screw groove and the surface of the ball. As a result, wear and plastic deformation of these components become less likely, and a linear actuator with superior durability can be obtained.

[0028] (Feature composition) In the linear actuator according to the present invention, the linear guide portion comprises at least two linear balls distributed around the rotation axis, The first engaging portion provided on the linear motion member and the second engaging portion provided on the housing engage with the linear motion ball, thereby preventing the rotation of the linear motion member around the rotation axis. It is preferable that at least one of the first engaging portion and the second engaging portion has a linear groove portion on which the linear ball can roll parallel to the axis of rotation.

[0029] (effect) This configuration provides smoother support by installing linear balls in the support sections of the ball holder and screw components that are not rotationally driven (linear components). By installing linear balls between the linear component and the housing, the reciprocating movement of the linear component along the rotation axis becomes smoother.

[0030] Furthermore, in this configuration, since the linear motion ball can roll parallel to the rotation axis within the linear motion groove, friction with respect to the linear motion ball is suppressed at least in either the first engagement part or the second engagement part. As a result, the linear motion of the linear motion member becomes extremely smooth, and a linear motion actuator with extremely low overall driving resistance can be obtained. [Brief explanation of the drawing]

[0031] [Figure 1] Cross-sectional view showing the configuration of a linear actuator according to the first embodiment. [Figure 2] Exploded perspective view showing the configuration of a linear actuator according to the first embodiment. [Figure 3] External view showing the screw of the linear actuator according to the first embodiment. [Figure 4] Developed view showing the shape of the groove formed in the screw according to the first embodiment. [Figure 5] Developed view showing the shape of the groove formed in the screw according to the third embodiment. [Figure 6] Cross-sectional view showing the configuration of a linear actuator according to the fourth embodiment. [Modes for carrying out the invention]

[0032] [First Embodiment] (overview) As shown in Figures 1 and 2, the linear actuator A according to the present invention comprises a drive unit 7 equipped with an electric motor or the like, and a linear member 2 that performs linear reciprocating motion based on the rotational motion of the drive unit 7. It can be used, for example, to operate a vehicle's parking brake or transmission. In particular, the linear member 2 uses a screw 2a via a ball 3, which can efficiently convert the driving force of the drive unit 7 into linear reciprocating motion.

[0033] Furthermore, the screw groove 2b provided in the screw 2a has regions with different lead angles, allowing the ball 3 to be fixed at a specific position in the screw groove 2b when the drive unit 7 is stopped. As a result, a linear actuator A that is not affected by reverse input to the screw 2a was obtained. The linear actuator A according to the first embodiment will now be described with reference to Figures 1 to 4.

[0034] (Drive unit) Figure 1 is a cross-sectional view showing the configuration of linear actuator A. In Figure 1, the area above the rotation axis X shows the screw 2a, which is the linear member 2, retracted into the housing H, while the area below the rotation axis X shows the end of the screw 2a protruding from the housing H. As the drive unit 7, a brushed or brushless DC motor, a stepping motor, or a servo motor with an encoder can be used. In particular, using a servo motor that can accurately control the rotation angle will result in accurate position control of the screw 2a.

[0035] The motor 7a, which serves as the drive unit 7, consists of a stator 7a1 fixed to the housing H and a rotor 7a2 integrally fitted onto a cylindrical ball holder 1a. The ball holder 1a is located inside the housing H and is supported by a first shaft support 8a and a second shaft support 8b, both of which use bearings. The bearing of the first shaft support 8a is fixed to the ball holder 1a by a first stage 1c formed on the ball holder 1a and a C-shaped first retaining member 9a fixed to the outer surface of the ball holder 1a. The second shaft support 8b is fixed in position by a second stage 1d formed on the ball holder 1a and a C-shaped second retaining member 9b fixed to the inner surface of the housing H.

[0036] (Extensible part) In this embodiment, the rotating shaft of the motor 7a is configured as a hollow ball holder 1a, with a screw 2a inserted inside it. In this embodiment, the ball holder 1a becomes the rotating member 1. At least one ball 3 is held in the wall portion of the ball holder 1a and engages with a screw groove 2b having a partially circular cross-sectional shape formed on the surface of the screw 2a.

[0037] A ball-holding hole 1b is formed in the wall of the ball holder 1a, for example, near the center along the rotation axis X, to rotatably hold a ball 3. The number of balls 3 matches the number of screw grooves 2b, and the number of balls 3 changes from one to three depending on whether the screw grooves 2b are configured as one, two, or three grooves. When there are multiple balls 3, the ball-holding holes 1b are evenly distributed around the rotation axis X at positions in the wall of the ball holder 1a that intersect with a plane perpendicular to the rotation axis X. The example shown in Figures 1 and 2 has two screw grooves 2b and uses two balls 3.

[0038] The ball-holding hole 1b is a circular hole having an inner diameter slightly larger than the diameter of the ball 3. The ball 3 held in the ball-holding hole 1b is held so that its surface protrudes by a predetermined distance from the inner and outer surfaces of the wall portion of the ball holder 1a.

[0039] A cylindrical sleeve 4 is provided on the outside of the ball holder 1a and the ball 3, which contacts the ball 3 and is fitted onto the ball holder 1a. The sleeve 4 restricts the displacement of the ball 3 away from the rotation axis X, eliminating play between the ball 3 and the screw groove 2b and ensuring secure engagement between the two.

[0040] The sleeve 4 is capable of relative rotation with respect to the ball holder 1a and relative movement along the rotation axis X. In other words, the sleeve 4 rotates and moves along the rotation axis X due to the balls 3 rolling in contact with the screw groove 2b. This reduces the rotational resistance of the balls 3, resulting in smoother driving of the screw 2a and improving the driving efficiency of the linear actuator A.

[0041] Inside the housing H, a space is formed that allows the sleeve 4 to move a predetermined distance along the rotation axis X. The sleeve 4 is reciprocally movable between a third stage portion 1e provided on the outer surface of the ball holder 1a and a C-shaped third retaining member 9c.

[0042] The screw 2a comprises a main body portion 21 having a screw groove 2b and a rod portion 22 protruding from the main body portion 21 in the direction of the rotation axis X. The screw 2a, which is the linear motion member 2, is located inside the ball holder 1a and is supported by two balls 3 in a non-contact state with the inner surface of the ball holder 1a.

[0043] The rod portion 22 forms a linear motion guide portion 5 with a cylindrical linear motion holding portion 51 provided in the housing H. The surface of the rod portion 22 is provided with, for example, three first engagement portions 22a that extend parallel to the rotation axis X. The first engagement portions 22a are essentially thrust grooves, and are provided in a manner that they are evenly distributed in the circumferential direction when viewed along the rotation axis X. The groove shape of the first engagement portions 22a is also partially circular, similar to the screw groove 2b. At least one linear motion ball 50 is arranged in each of these first engagement portions 22a.

[0044] Meanwhile, the linear motion holding portion 51, which is provided on the outside of the rod portion 22, also has three second engagement portions 51a that extend parallel to the rotation axis X. The linear motion ball 50 engages with the second engagement portions 51a, thereby causing the screw 2a to reciprocate non-rotatably relative to the housing H. The linear motion holding portion 51 has an inwardly facing flange 51b on the inner side to define the rolling range of the linear motion ball 50, and a cover member 52 is attached to the other end.

[0045] As shown in this configuration, by making both the first engaging portion 22a and the second engaging portion 51a linear grooves along the rotation axis X, the linear ball 50 rolls against both the first engaging portion 22a and the second engaging portion 51a during the reciprocating movement of the rod portion 22. Therefore, friction between the linear ball 50 and the first engaging portion 22a, and friction between the linear ball 50 and the second engaging portion 51a are reduced, resulting in extremely smooth reciprocating movement of the screw 2a.

[0046] (Detailed structure of the screw groove) The screw groove 2b of this embodiment has two regions, each having a different lead angle. Specifically, there is a first region R1 having a first lead angle α that causes the screw 2a to reciprocate along the rotation axis X when the ball holder 1a is rotated by the drive unit 7, and a second region R2 having a second lead angle β that pauses the reciprocating movement of the screw 2a regardless of the rotational drive of the ball holder 1a.

[0047] In this embodiment, for example, as shown in Figures 3 and 4, a first region R1 is provided in the central region of the screw groove 2b, and second regions R2 are provided at both ends of this first region R1. In Figure 4, the horizontal axis shows the circumferential position due to the rotation of the screw 2a, and the vertical axis shows the position in the linear direction along the rotation axis X. Here, the second lead angle β is set to approximately zero. Strictly speaking, "approximately zero" means that, as shown in Figures 3 and 4, a concave portion 2b1 is formed that is slightly offset in the direction along the rotation axis X, and the ball 3 is configured to be stable at the bottom of the concave portion 2b1.

[0048] In this configuration, for example, if an external force is applied to the rod portion 22 of the screw 2a in a direction that pushes the screw 2a in the direction of the rotation axis X, the ball 3 is pressed against the bottom of the concave portion 2b1, and the position of the screw 2a is stably fixed.

[0049] (Biasing member) For example, the biasing member 6 is brought into contact with the rod portion 22 of the screw 2a so that the ball 3 is pressed toward the bottom of the concave portion 2b1. As shown in Figures 1 and 2, a coil spring is provided as the biasing member 6 between a part of the housing H and the rod portion 22.

[0050] By providing a concave portion 2b1 in the second region R2 and pressing the screw 2a with the biasing member 6, the stationary state of the ball 3 relative to the concave portion 2b1 is stabilized. Therefore, the control of the stationary position of the drive unit 7 is simplified, and a simple linear actuator A can be constructed.

[0051] Furthermore, even if a reverse input such as pushing the screw 2a is applied while the motor 7a is idle, the screw 2a can be self-locked. In addition, since power consumption is not required when the motor 7a is idle, a power-saving linear actuator A can be obtained.

[0052] In addition, when a second region R2 is formed at the end of the screw groove 2b, the ball 3 will rest at the bottom of the concave portion 2b1 when the drive unit 7 comes to a stop. Therefore, the ball 3 will not collide with the end of the screw groove 2b, and the generation of vibration and noise at the start and end of the reciprocating movement can be prevented.

[0053] Furthermore, if the biasing member 6 is configured to press against the screw 2a, the ball 3 is always pressed against one wall of the screw groove 2b. Therefore, play between the ball holder 1a and the screw 2a is less likely to occur, resulting in a quiet and high-quality linear actuator A.

[0054] In addition to the above embodiment, a second region R2 can also be provided such that the screw groove 2b is located in a planar plane perpendicular to the rotation axis X, without providing a concave portion 2b1 as the second region R2.

[0055] The motor 7a used for driving typically has some rotational resistance, and some types of motor 7a also generate cogging torque. Therefore, even if the second lead angle β in the second region R2 is so-called zero degrees, as long as the direction of the reverse input to the screw 2a is aligned with the rotation axis X, the rotational resistance of the motor 7a ensures that the screw 2a remains reliably stopped.

[0056] Although not shown in the diagram, the first lead angle α in the first region R1 does not necessarily have to be constant, as shown in Figure 4. For example, if the load changes depending on the reciprocating position of the linear motion member 2 due to the characteristics of the object being linearly operated, the first lead angle α may be changed according to the load fluctuations. This ensures that the rotational speed of the drive unit 7 remains constant, resulting in smoother rotational operation of the drive unit 7. As a result, the required torque value of the motor 7a becomes clear, allowing for a more rational selection of the motor 7a. Furthermore, the reduced fluctuation in drive torque can improve the durability of the motor 7a.

[0057] [Second Embodiment] Regarding the configuration of the screw groove 2b, for example, as shown in Figure 5, three second regions R2 may be provided. Therefore, three concave portions 2b1 are provided along the direction of the rotation axis X. Thus, the number of concave portions 2b1 is arbitrary.

[0058] With this configuration, the fixed position of the ball 3 on the screw 2a can be arbitrarily set. This configuration is effective, for example, when used as an actuator to switch shift positions in an automatic transmission that requires multiple fixed positions. Power is not consumed when holding the shift position at each position, resulting in an energy-saving shift device.

[0059] [Third Embodiment] The sleeve 4, which prevents the ball 3 from flying out of the ball holder 1a, can be provided with a spiral second screw groove 2c on its inner surface that extends in the direction of the ball 3's rolling, as shown in the sleeve 4a in Figure 2.

[0060] By providing such a second screw groove 2c and allowing the ball 3 to roll in it, the relative position of the sleeve 4a with respect to the ball 3 is more restricted compared to the case where the second screw groove 2c is not provided. As a result, the movement of the sleeve 4a due to inertia is suppressed, for example, when a vehicle equipped with the linear actuator A accelerates or decelerates. Consequently, vibration and noise are prevented from occurring when the sleeve 4a collides with the third stage portion 1e or the third stopper member 9c at the moving end point.

[0061] Furthermore, if the shape of the second screw groove 2c, that is, the contour of the second screw groove 2c in a cross-section perpendicular to the longitudinal direction of the second screw groove 2c, is substantially circular, then line contact between the ball 3 and the surface of the second screw groove 2c becomes possible, reducing stress concentration on the surface of the screw groove 2b and the surface of the ball 3. As a result, wear and plastic deformation are less likely to occur in these components, and a linear actuator A with excellent durability can be obtained.

[0062] [Fourth Embodiment] As shown in Figure 6, the overall length of the linear actuator A of the present invention can be further reduced. In this configuration, the sleeve 4 and the linear ball 50 do not move along the direction of the rotation axis X.

[0063] The sleeve 4 is configured to have a short length along the direction of the rotation axis X. The sleeve 4 is held in place by the third stage 1e and the third retaining member 9c so that it can only rotate relative to the ball holder 1a. Therefore, when the ball holder 1a rotates, the frictional force between the ball 3 and the sleeve 4 becomes somewhat large. However, with this configuration, the movement area of ​​the screw 2a can be overlapped with the inside of the first shaft support 8a, and the overall length along the rotation axis X can be reduced.

[0064] Furthermore, the linear motion ball 50 is fixed in position relative to the linear motion holding part 51. As a result, although the linear motion ball 50 rotates relative to the first engagement part 22a of the rod part 22, some friction occurs between it and the second engagement part 51a of the linear motion holding part 51. However, by using the linear motion ball 50, the friction generated is extremely small compared to ordinary sliding bearings, and smooth reciprocating motion characteristics can be obtained.

[0065] Furthermore, in this configuration, the length of the linear motion holding section 51 along the rotation axis X is significantly reduced, making the linear motion actuator A even more compact. [Industrial applicability]

[0066] The linear actuator of the present invention can be widely used in mechanisms that require linear reciprocating motion controlled by a drive unit, and that need to lock the reciprocating motion when the drive unit is idle. [Explanation of symbols]

[0067] 1 Rotating member 1a Ball holder 2 Linear motion member 2a Screw 2b Screw groove 2b1 Concave part 2c Second screw groove 22a First engaging part 3 balls 4 sleeves 5 Linear motion guide unit 50 Linear Ball 51a Second engaging part 6. Biasing member 7 Drive Unit α First lead angle β Second lead angle A Linear Actuator H Housing R1 1st area R2 2nd area X Rotation axis

Claims

1. a cylindrically formed ball holder; At least one ball rotatably held on a wall of the ball holder; a screw having a screw groove on its outer surface with which the ball engages, the screw being inserted into the ball holder; a driving unit that drives one of the ball holder and the screw (rotating member) to rotate around a rotation axis; a housing in which the ball holder, the screw, and the drive portion are provided; a linear motion guide portion that is provided between the housing and a member (linear motion member) of the ball holder and the screw that is not rotationally driven, and that thrust-moves the linear motion member, A linear actuator, wherein the screw groove has a first region having a first lead angle that causes the screw and the ball holder to move back and forth relative to each other along the rotation axis when the drive unit is rotationally driven, and a second region having a second lead angle that causes the relative reciprocating movement to stop regardless of the rotational drive.

2. 2. The linear actuator according to claim 1, wherein the second region has a recessed portion whose lead angle with respect to the rotation axis is reversed.

3. 3. The linear actuator according to claim 2, wherein a biasing member is in contact with at least one of the ball holder and the screw so as to press the ball toward the bottom of the recessed portion.

4. 4. The linear actuator according to claim 1, wherein a cylindrical sleeve that holds the ball and abuts against the ball is fitted onto the ball holder, and the sleeve is configured to be able to move along the rotation axis and rotate around the rotation axis relative to the ball holder.

5. 5. The linear actuator according to claim 4, wherein a second spiral screw groove is provided on the inner surface of the sleeve, the second screw groove abutting against the ball that rolls in contact with the screw and extending in the rolling direction of the ball.

6. the linear guide portion includes at least two linear balls distributed around the rotation axis, a first engaging portion provided on the linear motion member and a second engaging portion provided on the housing engage with the linear motion ball to prevent rotation of the linear motion member around the rotation axis; 6. The linear actuator according to claim 1, wherein at least one of the first engagement portion and the second engagement portion has a linear groove portion formed therein, in which the linear ball can roll parallel to the rotation axis.

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