Ball screws and linear actuators

Abstract

To provide a ball screw which can suppress a deformation of a screw shaft and a fall of rotation prohibition means from the screw shaft.SOLUTION: In a ball screw 4 having a screw shaft 20, a nut 15, a rotation prohibition ring 30 attached to a tip circumferential part 24 of a tip side of the screw shaft 20, and movement regulation means 40 for regulating the movement of the rotation prohibition ring 30 in an axial direction, and used in a linear motion actuator 1 in which a rotational motion of the nut 15 is converted to a linear motion of the screw shaft 20, the rotation prohibition ring 30 comprises: a ring member 31; an outside protrusion 32 protruding from an external peripheral face of the ring member 31; and an inside protrusion 33 protruding from an internal peripheral face of the ring member 31. The outside protrusion 32 has parallel two guide faces 34 protruding from the external peripheral face 26 of the ring member 31, and chamfered parts 35 are formed at both end parts of the guide faces 34 in the axial direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0006] , ,

[0001] The present invention relates to a ball screw that converts the rotational motion transmitted to a rotational motion element into a linear motion, and a linear actuator provided with the ball screw.

Background Art

[0002] This type of linear actuator has a ball screw mechanism having a ball screw shaft and a ball screw nut that is screwed to the ball screw shaft via a large number of balls, and uses one of the ball screw shaft and the ball screw nut as a rotational motion element that rotationally drives the other, and uses the other as a linear motion element that linearly moves the other. At this time, in order for the linear motion element to linearly move, it is necessary to prevent it from rotating together with the rotational motion element. Usually, a guide projection formed on the linear motion element is engaged with a guide groove formed in the axial direction in a fixed portion to prevent rotation.

[0003] For example, in the electric actuator disclosed in Patent Document 1, a nut rotatably and non-axially movably attached to a housing, and a screw shaft screwed to the nut are provided, and a locking pin protruding radially is provided at an end of the screw shaft as a rotation preventing means for the screw shaft. A concave groove extending in the axial direction is formed in the housing, and the locking pin is engaged with the concave groove so that the screw shaft is non-rotatable and axially movable with respect to the housing.

[0004] The locking pin provided at the end of the screw shaft shown in Patent Document 1 is provided with a pin hole in the screw shaft, and the locking pin is press-fitted and fixed to the pin hole to prevent it from coming off.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a structure in which a locking pin is fixed to a screw shaft by press-fitting, as shown in Patent Document 1, if the screw shaft is hollow, the engagement area between the locking pin and the screw shaft is small, and there is a concern that the pin hole may widen or become elliptical due to repeated sliding of the pin, causing the locking pin to come out. In addition, when press-fitting the locking pin onto the screw shaft, a load is applied in the radial direction of the screw shaft, which may cause the cross-section of the screw shaft to deform into an ellipse.

[0007] Furthermore, when electric actuators are used in applications such as electric brakes in automobiles, compactness is desirable because they are installed inside the tire wheel. However, the structure in which the locking pin is fixed to the screw shaft by press-fitting requires a certain amount of engagement between the locking pin and the tip surface of the screw shaft. This limits the axial reduction, making compactness difficult.

[0008] In view of the above problems, the present invention provides a ball screw and a linear actuator that are compact and can suppress deformation of the screw shaft and detachment of the rotation-preventing means from the screw shaft. [Means for solving the problem]

[0009] One aspect of the present invention is a ball screw used in a linear actuator in which the rotational motion of the nut is converted into linear motion of the screw shaft, comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove formed on its inner circumference corresponding to the screw groove of the screw shaft; a tip circumferential portion formed on the tip side of the screw shaft with a circular outer circumference; a rotation-restricting means attached to the tip circumferential portion; and a movement-restricting means that restricts the axial movement of the screw shaft of the rotation-restricting means, wherein the rotation-restricting means comprises a ring-shaped ring member attached to the outer circumference of the tip circumferential portion, and a ring The ball screw comprises an outer projection that protrudes radially outward from the outer circumferential surface of the ring member and an inner projection that protrudes radially inward from the inner circumferential surface of the ring member. An insertion groove is formed in the tip circumference, extending from the tip end face to the outer circumferential surface. The rotation prevention means is mounted so as not to rotate relative to the tip circumference by inserting the inner projection into the insertion groove. The outer projection protrudes radially from the outer circumferential surface of the ring member and has two planes that are parallel to each other and parallel to the axis of the ring member, with chamfers formed on both axial ends of the two parallel planes.

[0010] Another aspect of the present invention is a linear actuator equipped with a ball screw according to one aspect, comprising: a housing; a bearing supported by the housing and supporting a nut rotatably but immovably in the axial direction relative to the housing; a motor mounted on the housing and transmitting rotational motion to the nut; and a guide groove formed within the housing and extending in the axial direction of the screw shaft to slide-support an outer projection of a rotation-preventing means, wherein the rotational motion of the nut causes the screw shaft to move axially but immovably relative to the housing. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a ball screw and a linear actuator that are compact and can suppress deformation of the screw shaft and detachment of the rotation-preventing means from the screw shaft. [Brief explanation of the drawing]

[0012] [Figure 1]This is a longitudinal cross-sectional view of the linear actuator according to the embodiment, showing the screw shaft moved to the left relative to the nut. [Figure 2] This is a longitudinal cross-sectional view of the linear actuator according to the embodiment, showing the screw shaft moved to the right relative to the nut. [Figure 3] This is a perspective view showing the linear actuator according to the embodiment with the housing removed. [Figure 4] This is a perspective view showing the linear actuator according to the embodiment with the housing removed and the rotation-preventing ring removed. [Figure 5] These figures show the front, side, and top views of the rotation-preventing ring of the ball screw according to this embodiment. [Figure 6] This diagram shows the front and side views of the screw shaft of the ball screw according to the embodiment. [Figure 7] This is a longitudinal cross-sectional view showing a movement-preventing means as a first embodiment of the ball screw according to the embodiment. [Figure 8] This is a longitudinal cross-sectional view showing a movement-preventing means as a second embodiment of the ball screw according to the embodiment. [Figure 9] This is a longitudinal cross-sectional view showing a movement-preventing means as a third embodiment of the ball screw according to the embodiment. [Figure 10] This is a longitudinal cross-sectional view showing a movement-preventing means as a fourth embodiment of the ball screw according to the embodiment. [Figure 11] This is a longitudinal cross-sectional view showing a movement-preventing means as a fifth embodiment of the ball screw according to the embodiment. [Figure 12] This is a longitudinal cross-sectional view showing a movement-preventing means as a sixth embodiment of the ball screw according to the embodiment. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described in detail while referring to the drawings. Note that the embodiments of the present invention shown below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the configuration, arrangement, etc. of the components as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

Example

[0014] FIG. 1(a) is a longitudinal sectional view of the linear actuator 1 according to the present embodiment, and FIG. 1(b) is a front view of the linear actuator 1 according to the present embodiment. Note that the longitudinal sectional view of FIG. 1(a) is a longitudinal sectional view taken along the B-B arrow view shown in FIG. 1(b). Further, FIG. 1(a) is a longitudinal sectional view in a state where the screw shaft 20 has moved to the left side with respect to the nut 15. Further, FIG. 2 is a longitudinal sectional view in a state where the screw shaft 20 of the linear actuator 1 according to the present embodiment has moved to the right side with respect to the nut 15. Note that the longitudinal sectional view described in the present embodiment refers to a sectional view of a plane along the axial direction.

[0015] The linear actuator 1 showing an embodiment of the present invention includes a cylindrical housing 2 having one end face open and the other end closed, a ball screw 4 attached to the housing 2 inside the housing 2, and a radial bearing 3 that supports the ball screw 4 with respect to the housing 2. The housing 2 is made of an aluminum alloy and includes a large cylindrical portion 10 on one end face side and a small cylindrical portion 11 joined to the end face of the large cylindrical portion 10. A large-diameter hole portion 12 is formed inside the large cylindrical portion 10, and a small-diameter hole portion 13 having a smaller diameter than the large-diameter hole portion 12 is formed inside the small cylindrical portion 11.

[0016] The outer ring of the bearing 3 is held on the inner peripheral surface of the large-diameter hole portion 12, and the outer ring of the bearing 3 is held so as not to be rotatable with respect to the housing 2 and not to be movable in the axial direction of the housing 2.

[0017] The ball screw 4 comprises a screw shaft 20 having a helical screw groove 22 formed on its outer circumference, a nut 15 fitted onto the screw shaft 20 and having a helical screw groove 16 formed on its inner circumference corresponding to the screw groove 22 of the screw shaft 20, and a plurality of balls 17 housed in a rolling path 18 formed between the screw groove 22 of the screw shaft 20 and the screw groove 16 of the nut 15. Therefore, in the ball screw 4, if the screw shaft 20 is supported in a way that prevents rotation, the rotational motion of the nut 15 is converted into linear motion of the screw shaft 20. Also, if the nut 15 is supported in a way that prevents rotation, the rotational motion of the screw shaft 20 is converted into linear motion of the nut 15. In this embodiment, the ball screw 4 is configured such that the screw shaft 20 is supported in a way that prevents rotation, and the rotational motion of the nut 15 is converted into linear motion of the screw shaft 20.

[0018] The inner ring of the bearing 3 is held on the outer surface of the nut 15, and the inner ring of the bearing 3 is held so as not to rotate relative to the nut 15 and so as not to move the nut 15 in the axial direction. Therefore, the nut 15 is supported by the housing 2 via the bearing 3 so as to be rotatable relative to the housing 2, but not so as to move in the axial direction of the housing 2. The ball screw 4 is attached to the housing 2 via the bearing 3, and with the ball screw 4 attached to the housing 2 via the bearing 3, the axes of the screw shaft 20, the nut 15, and the bearing 3 coincide, and the axes of the screw shaft 20, the nut 15, and the bearing 3 also coincide with the axes of the large diameter hole 12 and the small diameter hole 13 of the housing 2 (hereinafter referred to as the axis of the housing 2).

[0019] An electric motor (not shown) is attached to the housing 2, and the nut 15 rotates via a reduction mechanism (not shown) driven by the electric motor.

[0020] A guide groove 14 is formed on the inner circumferential surface of the small-diameter hole 13 of the housing 2, extending in the axial direction of the housing 2 and providing sliding support for a rotation-preventing ring 30, which will be mounted on the tip of the screw shaft 20. The rotation-preventing ring 30 is the rotation-preventing means in this invention. The guide groove 14 is formed concavely on the inner circumferential surface of the small-diameter hole 13 in a cross section perpendicular to the axis of the housing 2, and has planar guide groove surfaces 19 that are parallel to each other and provide sliding support for the rotation-preventing ring 30. As will be described in detail later, the rotation-preventing ring 30 is mounted on the screw shaft 20 so as to be unable to rotate and unable to move in the axial direction of the screw shaft 20. Therefore, by providing sliding support for the rotation-preventing ring 30 mounted on the screw shaft 20 with respect to the guide groove 14, the screw shaft 20 can move in the axial direction without rotating. Furthermore, as will be described in detail later, in Figure 1, a crimping portion 40 is provided at a position on the tip side of the screw shaft 20 relative to the rotation-preventing ring 30, serving as a movement-restricting means to restrict the axial movement of the rotation-preventing ring 30 relative to the screw shaft 20.

[0021] In the linear actuator 1, the nut 15 rotates when driven by an electric motor. Due to the rotation of the nut 15, the screw shaft 20, which is supported in a way that prevents rotation by a guide groove 14 formed in the housing 2, can move linearly in the axial direction. Figure 1(a) shows the state in which the screw shaft 20 of the linear actuator 1 has moved to the left relative to the nut 15. Figure 2 shows the state in which the screw shaft 20 of the linear actuator 1 has moved to the right relative to the nut 15 due to the rotation of the nut 15.

[0022] Next, the details of the ball screw 4 will be explained using Figures 3 and 4. Figure 3 is a perspective view showing the linear actuator 1 without its housing 2 and with the rotation-preventing ring 30 removed. Figure 4 is a perspective view showing the linear actuator 1 with its housing 2 removed and the rotation-preventing ring 30 installed. Both Figures 3 and 4 show the bearing 3 attached to the nut 15 of the ball screw 4.

[0023] As described above, the ball screw 4 comprises a nut 15 and a screw shaft 20. In Figures 3 and 4, a bearing 3 is attached to the outer circumference of the nut 15. The screw shaft 20 is hollow at the center and has a hollow portion 28. The screw shaft 20 has a screw portion 21 with screw grooves 22 formed on its outer circumference and a tip circumferential portion 24 at the tip of the screw shaft 20 where screw grooves 22 are not formed on the outer circumference. The outer diameter of the tip circumferential portion 24 is smaller than the root diameter of the screw grooves 22. An insertion groove 27 is formed on the tip circumferential portion 24, extending from the tip end face 25 to the outer circumferential surface 26. The rotation-preventing ring 30 comprises a ring-shaped ring member 31 mounted on the outer circumferential surface 26 of the tip circumferential portion 24, an outer projection 32 protruding radially outward from the outer circumferential surface of the ring member 31, and an inner projection 33 protruding radially inward from the inner circumferential surface of the ring member 31. The inner projection 33 of the rotation-preventing ring 30 is inserted into the insertion groove 27. By inserting the inner projection 33 into the insertion groove 27 and mounting the rotation-preventing ring 30 on the outer surface 26 of the tip circumference 24, the rotation-preventing ring 30 does not rotate relative to the tip circumference 24. Figure 4 shows the state in which the inner projection 33 of the rotation-preventing ring 30 is inserted into the insertion groove 27 and the rotation-preventing ring 30 is mounted on the outer surface 26 of the tip circumference 24.

[0024] Next, the rotation-preventing ring 30 as a rotation-preventing means will be described using Figure 5. In Figure 5, (a) is a front view of the rotation-preventing ring 30, (b) is a side view of the rotation-preventing ring 30, and (c) is a top view of the rotation-preventing ring 30. The rotation-preventing ring 30 is made of resin and includes a ring-shaped ring member 31 that is attached to the outer circumferential surface 26 of the tip circumference 24, an outer projection 32 that protrudes radially outward from the outer circumferential surface of the ring member 31, and an inner projection 33 that protrudes radially inward from the inner circumferential surface of the ring member 31.

[0025] The outer projections 32 are provided at two locations on the ring member 31 at positions 180 degrees apart in the circumferential direction. Similarly, the inner projections 33 are also provided at two locations on the ring member 31 at positions 180 degrees apart in the circumferential direction. The outer projections 32 and inner projections 33 are positioned in the same phase in the circumferential direction of the ring member 31. Therefore, the rotation-preventing ring 30 is symmetrical left and right, symmetrical up and down, and has the same structure on both sides. This prevents incorrect assembly when mounting the rotation-preventing ring 30 on the outer circumferential surface 26 of the tip circumference 24. The axial width a of the outer projections 32 is smaller than the radial width b of the ring member 31. Furthermore, when the outer projections 32 and inner projections 33 are positioned in the same phase in the circumferential direction of the ring member 31, the time lag in torque transmission is reduced. If the outer projection 32 and the inner projection 33 are positioned at different phases in the circumferential direction of the ring member 31, the rotation-preventing ring 30, being made of resin, will undergo elastic deformation, causing the screw shaft 20 to rotate by the amount of that elastic deformation.

[0026] The outer projection 32 protrudes radially from the outer circumferential surface of the ring member 31 and has two guide surfaces 34 which are parallel to each other and parallel to the axis of the ring member 31. The guide surfaces 34 are slidably supported on the guide groove surface 19 of the guide groove 14 formed on the inner circumferential surface of the housing 2. Chamfered portions 35 are formed on both ends of the two parallel guide surfaces 34 in the axial direction. Although the guide surfaces 34 are slidably supported on the guide groove surface 19 of the guide groove 14, the surface pressure on the guide surfaces 34 can be reduced because the guide surfaces 34 are flat. In addition, since chamfered portions 35 are formed on both ends of the guide surfaces 34 in the axial direction, sliding resistance when the guide surfaces 34 are slidably supported on the guide groove surface 19 can be suppressed. In this embodiment, the chamfered portions 35 formed on both ends of the guide surfaces 34 in the axial direction may be R-chamfered. In this embodiment, the rotation-preventing ring 30 is made of resin, but it does not have to be made of resin and may be made of metal such as press-formed spring steel.

[0027] Next, the screw shaft 20 will be described using Figure 6. In Figure 6, (a) is a side view of the screw shaft 20, and (b) is a front view of the screw shaft 20. The screw shaft 20 has a hollow center and is provided with a hollow section 28. The screw shaft 20 has a screw section 21 with screw grooves 22 formed on its outer circumference, and a tip circumferential section 24 at the tip of the screw shaft 20 where screw grooves 22 are not formed on the outer circumference. The outer diameter of the tip circumferential section 24 is smaller than the root diameter of the screw grooves 22. The screw shaft 20 is a two-stage shaft in which the screw section end face 23, which is the end face of the screw section 21, and the outer circumferential surface 26 of the tip circumferential section 24 are formed at a 90-degree angle in the axial cross-section. An insertion groove 27 is formed in the tip circumferential section 24, extending from the tip end face 25 to the outer circumferential surface 26 and the inner circumferential surface of the hollow section 28. There are two insertion grooves 27 provided at positions 180 degrees apart in the circumferential direction of the tip circumferential section 24. Since the two insertion grooves 27 are located at positions 180 degrees apart in the circumferential direction of the tip circumference 24, the insertion grooves 27 can be formed in a single end milling operation.

[0028] Two inner protrusions 33 on the rotation-preventing ring 30 are inserted into the two insertion grooves 27. With the two inner protrusions 33 inserted into the two insertion grooves 27, the rotation-preventing ring 30 is mounted on the outer surface 26 of the tip circumference 24, so that the rotation-preventing ring 30 does not rotate relative to the tip circumference 24.

[0029] Furthermore, the two insertion grooves 27 are formed to extend into the threaded portion 21. That is, the ends of the two insertion grooves 27 on the threaded portion 21 side extend into the threaded portion 21. Because the two insertion grooves 27 are formed to extend into the threaded portion 21, even if a radius (R) is formed in the corners of the ends of the insertion grooves 27 on the threaded portion 21 side, the axial end face of the rotation-preventing ring 30 can be brought into close contact with the threaded portion end face 23. The threaded portion end face 23 serves as a movement-restricting means that restricts the movement of the rotation-preventing ring 30 in the axial direction of the screw shaft 20 toward the threaded portion 21 side.

[0030] Next, using Figures 7 to 12, a movement restricting means for restricting the movement of the rotation-preventing ring 30 in the axial direction of the screw shaft 20 toward the tip end face 25 of the tip circumference portion 24 will be explained.

[0031] Figure 7 is a longitudinal cross-sectional view showing a movement-restricting means as a first embodiment of the ball screw 4 according to this embodiment. On the outer circumferential surface 26 of the tip circumference 24 of the ball screw 4, a crimped portion 40 is provided at a position adjacent to the tip end face 25, which is formed by rising radially from the outer circumferential surface 26. The crimped portion 40 is located on the tip end face 25 side of the rotation-restricting ring 30 attached to the tip circumference 24. The crimped portion 40 is a movement-restricting means that restricts the axial movement of the rotation-restricting ring 30 in the present invention. This is a movement-restricting means as a first embodiment. The crimped portion 40 is formed by pressing the tip end face 25 from the direction indicated by the white arrow in Figure 7.

[0032] Figure 8 is a longitudinal cross-sectional view showing a movement-restricting means as a second embodiment of the ball screw 4 according to this embodiment. A crimping portion 40 is provided on the inner surfaces of the insertion groove 27 formed in the tip circumference 24, at a position adjacent to the tip end face 25, where they face each other and are raised from the inner surfaces. The crimping portion 40 is located on the tip end face 25 side of the rotation-restricting ring 30 mounted on the tip circumference 24. The crimping portion 40 is a movement-restricting means that restricts the axial movement of the rotation-restricting ring 30 in the present invention. The crimping portion 40, which is the movement-restricting means as a second embodiment, is formed when a jig that enters the insertion groove 27 presses the corner formed between the tip end face 25 and the inner circumference of the insertion groove 27 from the direction indicated by the white arrow in Figure 8.

[0033] Figure 9 is a longitudinal cross-sectional view showing a movement-restricting means as a third embodiment of the ball screw 4 according to this embodiment. A crimped portion 40 is formed at the corners formed by the opposing inner surfaces of the insertion groove 27, the tip end face 25 of the tip circumference 24, and the outer circumferential surface 26, rising from the opposing inner surfaces and outer circumferential surface 26 of the insertion groove 27. A crimped portion 40 is also formed at the corners formed by the opposing inner surfaces of the insertion groove 27, the tip end face 25 of the tip circumference 24, and the inner circumferential surface of the hollow portion 28, rising from the opposing inner surfaces of the insertion groove 27 and the inner circumferential surface of the hollow portion 28. The crimped portion 40 is located on the tip end face 25 side of the rotation-restricting ring 30 mounted on the tip circumference 24. The crimped portion 40 is a movement-restricting means that restricts the axial movement of the rotation-restricting ring 30 in the present invention. Furthermore, it is not necessary to provide crimping portions 40 at the corners formed by the opposing inner surfaces of the insertion groove 27, the tip end face 25 of the tip circumference portion 24, and the inner circumferential surface of the hollow portion 28.

[0034] Figure 10 is a longitudinal cross-sectional view showing a movement-restricting means as a fourth embodiment of the ball screw 4 according to this embodiment. On the outer circumferential surface 26 of the tip circumference 24 of the ball screw 4, a crimped portion 40 is formed that rises from the outer circumferential surface 26 at a position adjacent to the tip end face 25. The crimped portion 40 is located on the tip end face 25 side of the rotation-restricting ring 30 attached to the tip circumference 24. The crimped portion 40 is a movement-restricting means that restricts the axial movement of the rotation-restricting ring 30 in the present invention. The crimped portion 40, which is the movement-restricting means as a fourth embodiment, is formed by pressing the outer circumferential edge of the tip end face 25 with a jig from the direction indicated by the white arrow in Figure 10.

[0035] Figure 11 is a longitudinal cross-sectional view showing a movement-restricting means as a fifth embodiment of the ball screw 4 according to this embodiment. The rotation-restricting ring 30 attached to the tip circumference 24 of the ball screw 4 is restricted from moving in the axial direction by a fixing nut 41 attached to the outer circumferential surface 26 of the tip circumference 24. A screw groove for attaching the fixing nut 41 is formed on the outer circumferential surface 26 of the tip circumference 24. The fixing nut 41 is a movement-restricting means that restricts the axial movement of the rotation-restricting ring 30 in the present invention.

[0036] Figure 12 is a longitudinal cross-sectional view showing a movement-restricting means as a sixth embodiment of the ball screw 4 according to this embodiment. The rotation-restricting ring 30 mounted on the tip circumference 24 of the ball screw 4 is restricted from moving in the axial direction by a fixing retaining ring 42 attached to the outer circumferential surface 26 of the tip circumference 24. A groove for attaching the fixing retaining ring 42 is formed on the outer circumferential surface 26 of the tip circumference 24. The fixing retaining ring 42 is a movement-restricting means that restricts the axial movement of the rotation-restricting ring 30 in the present invention.

[0037] The manufacturing methods for the insertion groove 27 formed in the tip circumference 24 and the crimped portion 40 shown in the first to fourth embodiments will now be described. In the first manufacturing method, the outer diameter of the screw shaft 20 is ground and the insertion groove 27 is cut, and the screw groove 22 is rolled or cut. After that, the screw groove 22 is subjected to heat treatment such as high-frequency induction hardening. Then, the rotation-preventing ring 30 is inserted into the screw shaft 20 and the crimped portion 40 is formed using a jig.

[0038] The second manufacturing method involves grinding the outer diameter of the screw shaft 20 and then rolling or cutting the screw groove 22. After that, the screw groove 22 is subjected to heat treatment such as high-frequency induction hardening. After the heat treatment, the outer diameter of the tip circumference 24 is ground and the insertion groove 27 is cut. Then, the rotation-preventing ring 30 is inserted onto the screw shaft 20 and the crimped portion 40 is formed using a jig.

[0039] In this embodiment, the outer projections 32 are provided at two locations on the ring member 31 at 180-degree apart positions in the circumferential direction, but are not limited to this. There may be one outer projection 32, or three or more outer projections. Also, if there are two outer projections, they do not have to be at 180-degree apart positions in the circumferential direction of the ring member 31. However, in that case, the arrangement of the guide grooves 14 formed on the inner circumferential surface of the small-diameter hole 13 of the housing 2 must match the circumferential arrangement of the outer projections 32. Also, in this embodiment, the inner projections 33 are provided at two locations on the ring member 31 at 180-degree apart positions in the circumferential direction, but are not limited to this. There may be one inner projection 33, or three or more inner projections. Also, if there are two inner projections, they do not have to be at 180-degree apart positions in the circumferential direction of the ring member 31. Furthermore, in this embodiment, the outer projection 32 and the inner projection 33 are positioned in the same phase in the circumferential direction of the ring member 31, but this is not necessarily the case. The outer projection 32 and the inner projection 33 do not have to be positioned in the same phase in the circumferential direction of the ring member 31. If there are multiple inner projections 33 provided on the insertion groove 27 and the rotation-preventing ring 30, it is sufficient that the circumferential position of the insertion groove 27 and the circumferential position of the inner projections 33 provided on the rotation-preventing ring 30 are in the same phase. In addition, although the inner projections 33 are provided at two locations 180 degrees apart in the circumferential direction of the ring member 31, these two inner projections 33 may extend toward the center and be connected to each other.

[0040] In this embodiment, the screw shaft 20 has a hollow portion 28, but is not necessarily limited to this. A solid screw shaft without a hollow portion 28 is also acceptable.

[0041] Furthermore, in this embodiment, the insertion groove 27 is formed to extend into the threaded portion 21, but the insertion groove 27 may be formed without extending into the threaded portion 21.

[0042] In this embodiment, the screw shaft 20 was a two-stage shaft comprising a screw portion 21 with a helical screw groove 22 formed on its outer circumferential surface 26, and a tip circumferential portion 24 whose outer diameter is smaller than the root diameter of the screw groove 22 and which does not have a screw groove 22 formed on its outer circumferential surface. However, it is not necessarily limited to this, and the screw shaft 20 does not have to be a two-stage shaft.

[0043] Although the above description has been made with reference to a limited number of embodiments, the scope of the rights is not limited to those embodiments, and modifications of the embodiments based on the above disclosure will be obvious to those skilled in the art. [Explanation of symbols]

[0044] 1…Linear actuator, 2…Housing, 3…Bearing, 4…Ball screw, 10a…Shaft, 10…Large cylindrical section, 11…Small cylindrical section, 12…Large diameter hole section, 13…Small diameter hole section, 14…Guide groove, 15…Nut, 16…Screw groove, 17…Ball, 18…Rolling path, 19…Guide groove surface, 20…Screw shaft, 21…Screw section, 22…Screw groove, 23…Screw section end face, 24…Tip circumference section, 25…Tip side end face, 26…Outer circumference surface, 27…Insertion groove, 28…Hollow section, 30…Rotation prevention ring, 31…Ring member, 32…Outer projection, 33…Inner projection, 34…Guide surface, 35…Chamfered section, 40…Crimping section, 41…Fixing nut, 42…Fixing retaining ring

Claims

1. A ball screw used in a linear actuator, comprising a screw shaft having a helical screw groove formed on its outer circumference, a nut having a helical screw groove on its inner circumference corresponding to the screw groove of the screw shaft, a tip circumferential portion formed on the tip side of the screw shaft with a circular outer circumference, a rotation-preventing means attached to the tip circumferential portion, and a movement-restricting means that restricts the axial movement of the rotation-preventing means of the screw shaft, wherein the rotational motion of the nut is converted into linear motion of the screw shaft, The rotation-preventing means comprises a ring-shaped ring member attached to the outer circumferential surface of the tip circumference, an outer projection protruding radially outward from the outer circumferential surface of the ring member, and an inner projection protruding radially inward from the inner circumferential surface of the ring member. An insertion groove is formed in the circumferential portion of the tip, extending from the tip side end face to the outer circumferential surface. The rotation-preventing means is mounted so that the inner projection is inserted into the insertion groove and is immobile relative to the tip circumference. The outer projection protrudes radially from the outer surface of the ring member and has two planes that are parallel to each other and parallel to the axis of the ring member. Chamfers are formed at both ends in the axial direction of the two planes that are parallel to each other. A ball screw characterized in that the outer projection and the inner projection are provided at positions in the same phase in the circumferential direction of the ring member.

2. A ball screw used in a linear actuator, comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove on its inner circumference corresponding to the screw groove of the screw shaft; a tip circumferential portion formed on the tip side of the screw shaft with a circular outer circumference; a rotation-preventing means attached to the tip circumferential portion; and a movement-restricting means for restricting the axial movement of the screw shaft of the rotation-preventing means, wherein the rotational motion of the nut is converted into linear motion of the screw shaft, The rotation-preventing means comprises a ring-shaped ring member attached to the outer circumferential surface of the tip circumference, an outer projection protruding radially outward from the outer circumferential surface of the ring member, and an inner projection protruding radially inward from the inner circumferential surface of the ring member. An insertion groove is formed in the circumferential portion of the tip, extending from the tip side end face to the outer circumferential surface. The rotation-preventing means is mounted so that the inner projection is inserted into the insertion groove and is immobile relative to the tip circumference. The outer projection protrudes radially from the outer surface of the ring member and has two planes that are parallel to each other and parallel to the axis of the ring member. Chamfers are formed at both ends in the axial direction of the two planes that are parallel to each other. The aforementioned tip circumference has an outer diameter smaller than the root diameter of the screw groove, and the screw groove is not formed on its outer surface. The screw shaft has a screw portion on its outer circumference where a helical screw groove is formed, and a tip circumference portion on its outer circumference where the screw groove is not formed, and the end face of the screw portion and the outer circumference of the tip circumference portion are formed at a 90-degree angle in the axial cross-section, forming a two-stage shaft. The ball screw is characterized in that the insertion groove is formed to extend into the threaded portion.

3. A ball screw used in a linear actuator, comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove on its inner circumference corresponding to the screw groove of the screw shaft; a tip circumferential portion formed on the tip side of the screw shaft and having a circular outer circumference; a rotation-preventing means attached to the tip circumferential portion; and a movement-restricting means for restricting the axial movement of the screw shaft of the rotation-preventing means, wherein the rotational motion of the nut is converted into linear motion of the screw shaft, The rotation-preventing means comprises a ring-shaped ring member attached to the outer circumferential surface of the tip circumference, an outer projection protruding radially outward from the outer circumferential surface of the ring member, and an inner projection protruding radially inward from the inner circumferential surface of the ring member. An insertion groove is formed in the circumferential portion of the tip, extending from the tip side end face to the outer circumferential surface. The rotation-preventing means is mounted so that the inner projection is inserted into the insertion groove and is immobile relative to the tip circumference. The outer projection protrudes radially from the outer surface of the ring member and has two planes that are parallel to each other and parallel to the axis of the ring member. Chamfers are formed at both ends in the axial direction of the two planes that are parallel to each other. The movement restricting means is a crimping portion formed on the tip side of the rotation preventing means at the tip circumference, The crimped portion is a crimp formed by pressing the corner formed by the tip end face of the tip circumference and the opposing inner surfaces of the insertion groove from the tip end face side, causing it to bulge out from the opposing inner surfaces of the insertion groove, resulting in a ball screw.

4. A ball screw used in a linear actuator, comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove on its inner circumference corresponding to the screw groove of the screw shaft; a tip circumferential portion formed on the tip side of the screw shaft and having a circular outer circumference; a rotation-preventing means attached to the tip circumferential portion; and a movement-restricting means for restricting the axial movement of the rotation-preventing means of the screw shaft, wherein the rotational motion of the nut is converted into linear motion of the screw shaft, The rotation-preventing means comprises a ring-shaped ring member attached to the outer circumferential surface of the tip circumference, an outer projection protruding radially outward from the outer circumferential surface of the ring member, and an inner projection protruding radially inward from the inner circumferential surface of the ring member. An insertion groove is formed in the circumferential portion of the tip, extending from the tip side end face to the outer circumferential surface. The rotation-preventing means is mounted so that the inner projection is inserted into the insertion groove and is immobile relative to the tip circumference. The outer projection protrudes radially from the outer surface of the ring member and has two planes that are parallel to each other and parallel to the axis of the ring member. Chamfers are formed at both ends in the axial direction of the two planes that are parallel to each other. The movement restricting means is a crimping portion formed on the tip side of the rotation preventing means at the tip circumference, The crimped portion is a crimp formed by pressing the corner formed by the outer circumferential surface and the tip end face of the tip circumference in the insertion groove from the side of the tip end face, causing it to protrude from the opposing inner surfaces of the insertion groove and the outer circumferential surface of the tip circumference.

5. A linear actuator comprising a ball screw according to any one of claims 1 to 4, Housing and A bearing supported by the housing, which supports the nut so that it is rotatable and immovable in the axial direction relative to the housing, A motor is attached to the housing and transmits rotational motion to the nut, The housing includes a guide groove formed within it, extending in the axial direction of the screw shaft and providing sliding support for the outer projection of the rotation-preventing means, A linear actuator characterized in that, due to the rotational motion of the nut, the screw shaft moves axially and immobilely relative to the housing.

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