Ball screw device and actuator

Abstract

To provide a ball screw device capable of coupling a screw shaft and a shaft by fastening a nut, and capable of avoiding the breakage of circulation components.SOLUTION: A ball screw device is equipped with: a nut that has a female screw groove; a screw shaft that has a male screw groove, and a returning passage that extends in an axial direction parallel to an axis of the nut; a plurality of balls disposed in a rolling path composed of the female screw groove and the male screw groove; and a plurality of circulation components connecting the rolling path and the returning passage. The screw shaft has a shaft attaching hole made by penetrating center portions on both end surfaces of the screw shaft, and a first storage groove and a second storage groove that are made by depressing a part of both end surfaces of the screw shaft and located on the diametrically outer side of the shaft attaching hole. The returning passage is made by penetrating a part of a wall portion of the screw shaft between a bottom surface of the first storage groove and a bottom surface of a second storage groove, and the plurality of circulation components are stored in the first storage groove and the second storage groove.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a ball screw device and an actuator.

Background Art

[0002] A ball screw device is a device that converts rotational motion into linear motion, and comprises a nut, a screw shaft, and a plurality of balls disposed between the nut and the screw shaft. The ball screw device also includes a mechanism for circulating the balls. For example, the screw shaft disclosed in the following Patent Document 1 has a return passage passing through the central portion of the end face as viewed in the axial direction. The screw shaft has a groove formed by cutting radially inward from the outer circumferential surface, and a circulation component is accommodated in the groove. In addition, the circulation components in the following Patent Document 2 and Patent Document 3 are fixed to both end faces of the screw shaft.

Prior Art Literature

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problem to be Solved by the Invention

[0004] In recent years, the use of a ball screw device as an actuator by connecting a shaft to a screw shaft has been considered. One possible method of connecting the shaft to the screw shaft is to pass a portion of the shaft through the screw shaft and fasten the passed portion with a nut. However, the screw shaft in Patent Document 1 has a return passage in its center. Therefore, it is not possible to provide a mounting hole in the center of the screw shaft for passing a portion of the shaft through. Furthermore, in Patent Documents 2 and 3, since circulation components are arranged on both end faces, tightening the shaft with a nut will damage the circulation components.

[0005] This disclosure has been made in view of the above-mentioned problems, and aims to provide a ball screw device and actuator that enables connection between a screw shaft and a shaft by fastening a nut, and that can avoid damage to circulating parts. [Means for solving the problem]

[0006] To achieve the above objective, a ball screw device according to one aspect of the present disclosure comprises a screw shaft having a nut with a female screw groove, a male screw groove, and a return passage extending in an axial direction parallel to the axis of the nut, a plurality of balls arranged in a rolling path consisting of the female screw groove and the male screw groove, and a plurality of circulating parts connecting the rolling path and the return passage. The screw shaft has a shaft mounting hole formed by penetrating the center of both end faces of the screw shaft, and a first housing groove and a second housing groove formed by recessing a portion of both end faces of the screw shaft and located radially outward from the shaft mounting hole. The return passage is formed by penetrating a portion of the wall of the screw shaft between the bottom surface of the first housing groove and the bottom surface of the second housing groove. The plurality of circulating parts are housed in the first housing groove and the second housing groove.

[0007] The return passage is located radially outward from the center of the screw shaft, and a shaft mounting hole can be provided at the center of the screw shaft. The circulating components are housed in the first and second housing grooves. Therefore, when a portion of the shaft is inserted into the shaft mounting hole and fastened with a nut to connect the shaft to the screw shaft, the shaft and nut will tighten against both end faces of the screw shaft. Thus, the circulating components will not be damaged. Furthermore, since there are no circulating components interposed between the shaft and the screw shaft, the fixing strength of the shaft to the screw shaft is increased.

[0008] In one embodiment of the ball screw device described above, the nut and the screw shaft have a multi-start screw structure having a plurality of female screw grooves and a plurality of male screw grooves. The screw shaft has a plurality of first housing grooves arranged circumferentially apart from each other, a plurality of second housing grooves arranged circumferentially apart from each other, and a plurality of return passages arranged circumferentially apart from each other.

[0009] As the number of threads increases, the number of balls packed in the screw increases, and the load capacity of the ball screw device increases.

[0010] To achieve the above objective, an actuator according to one aspect of the present disclosure comprises the ball screw device described above, a shaft in which a portion is inserted into the shaft mounting hole, a shaft mounting nut for fastening the shaft, a motor having an output shaft, and a sealing member. The nut is a bottomed cylindrical shape with an opening at one end for incorporating the screw shaft. The sealing member closes the opening. The shaft extends outside the nut, passing through the sealing member. One of the nut and the shaft is connected to the output shaft and rotates by the drive of the output shaft, and the other of the nut and the shaft moves in the axial direction by the drive of the output shaft. The screw shaft has ventilation holes that pass through both end faces.

[0011] According to the actuator described above, the nut or shaft moves axially when the output shaft of the motor is driven, thereby moving the object. Furthermore, the opening of the nut is closed by the sealing member, sealing the inside of the nut. Therefore, it is difficult for foreign matter to enter the inside of the nut, and it is difficult for foreign matter to adhere to the male and female screw grooves. In addition, when the screw shaft moves away from the sealing member, the space between the screw shaft and the sealing member expands and the pressure is reduced. Then, the air in the space on the opposite side of the screw shaft from the sealing member flows into the space between the screw shaft and the sealing member through the air hole. As a result, the pressure reduction in the space between the screw shaft and the sealing member prevents foreign matter from being sucked in through the gap in the sealing member. [Effects of the Invention]

[0012] According to the ball screw device and actuator of this disclosure, a shaft can be connected to the screw shaft by fastening a nut. Furthermore, the circulating parts will not be damaged. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a side view of the actuator of Embodiment 1. [Figure 2] Figure 2 is an enlarged view of the screw shaft and its vicinity in Embodiment 1, extracted and enlarged. [Figure 3] Figure 3 is a cross-sectional view taken along the line III-III in Figure 1. [Figure 4] Figure 4 is a cross-sectional view taken along the line IV-IV in Figure 1. [Figure 5] Figure 5 is a cross-sectional view taken along the line III-III in Figure 1, with the lubrication components removed from the ball screw. [Figure 6] Figure 6 is a view of the circulating component of Embodiment 1 from the axial direction. [Figure 7] Figure 7 shows the circulating component of Embodiment 1 as viewed from the radially outer side. [Figure 8] Figure 8 shows a ball screw mechanism of a comparative example, viewed from the inner circumference. [Figure 9]Fig. 9 is a diagram showing an overall view of the ball screw device of a comparative example. [Figure 10] Fig. 10 is a side view of the actuator according to the second embodiment. [Figure 11] Fig. 11 is an enlarged view obtained by extracting and enlarging the screw shaft and the vicinity thereof according to the second embodiment. [Figure 12] Fig. 12 is a view of the second end surface of the screw shaft as seen from the motor side. [Figure 13] Fig. 13 is a side view of the actuator according to the third embodiment. [Figure 14] Fig. 14 is a view of the screw shaft according to the third embodiment as seen from the cover side. [Figure 15] Fig. 15 is a view of the screw shaft according to the third embodiment as seen from the seal member side. [Figure 16] Fig. 16 is a side view of the actuator according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited by the following modes for carrying out the invention (hereinafter referred to as "embodiments"). In addition, constituent elements in the following embodiments include those that can be easily conceived by those skilled in the art, those that are substantially identical, and those that fall within the so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be appropriately combined.

[0015] Fig. 1 is a side view of the actuator according to the first embodiment. Fig. 2 is an enlarged view obtained by extracting and enlarging the screw shaft and the vicinity thereof according to the first embodiment. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 1. Fig. 5 is a cross-sectional view taken along line III-III in Fig. 1 in a state where a lubricating component is removed from the ball screw. Fig. 6 is a view of the circulation component according to the first embodiment as seen from the axial direction. Fig. 7 is a view of the circulation component according to the first embodiment as seen from the radially outer side. Fig. 8 is a view of a top of the ball screw device of a comparative example as seen from the inner peripheral side. Fig. 9 is a diagram showing an overall view of the ball screw device of a comparative example.

[0016] (Embodiment 1) As shown in Figure 1, the actuator 100 comprises a motor 101, a ball screw device 1, a shaft 110, and a shaft mounting nut 120. The motor 101 has an output shaft 101a that rotates about axis X. The motor 101 is mounted on a base 102. The output shaft 101a of the motor 101 is parallel to the surface 102a of the base 102. Hereinafter, the direction parallel to axis X will be referred to as the axis X direction. Furthermore, within the axis X direction, the direction pointed to by the output shaft 101a will be referred to as the first direction X1, and the direction opposite to the direction pointed to by the output shaft 101a will be referred to as the second direction X2.

[0017] The ball screw device 1 comprises a nut 10, a screw shaft 20, a plurality of balls 30 positioned between the nut 10 and the screw shaft 20, and two circulating parts 40, 40 (see Figure 2). The nut 10 has a cylindrical portion 11 that forms a cylindrical shape around an axis X, a cover portion 12 that closes the end of the cylindrical portion 11 in a second direction X2, and a shaft portion 13 that extends from the cover portion 12 in the second direction X2.

[0018] A single female screw groove 14 is provided on the inner circumferential surface of the cylindrical portion 11. An opening 15 is provided at the end of the cylindrical portion 11 in the first direction X1. The screw shaft 20 is assembled inside the cylindrical portion 11 through the opening 15. A sealing member 16 is provided in the opening 15 of the cylindrical portion 11. This seals the inside of the cylindrical portion 11.

[0019] The shaft portion 13 is supported by a bearing device 2 installed on the base 102. The bearing device 2 comprises two rows of bearings 3, 3 and a fixing portion 4 that supports the two rows of bearings 3, 3. The two rows of bearings 3, 3 are arranged in a back-to-back configuration. A connecting hole 13a is provided on the end face of the shaft portion 13 in the second direction X2. The output shaft 101a is fitted into the connecting hole 13a, and the nut 10 and the output shaft 101a are integrated. A bearing device nut 13b is screwed onto the outer circumference of the shaft portion 13. The inner rings of the two rows of bearings 3, 3 are fastened to the cover portion 12 of the nut 10 and the bearing device nut 13b. This applies preload to the inner rings of the two rows of bearings 3, 3. The nut 10 is fixed to the bearing device 2 so as not to move in the direction of the axis X. When the motor 101 starts and the output shaft 101a rotates, the nut 10 also rotates around the axis X.

[0020] The screw shaft 20 is a cylindrical component whose length in the axial X direction is shorter than that of the cylindrical portion 11 of the nut 10. The screw shaft 20 has a first end face 21 facing a first direction X1 and a second end face 22 facing a second direction X2. The outer circumferential surface of the screw shaft 20 is provided with a single male screw groove 23 corresponding to the female screw groove 14. Multiple balls 30 are arranged in a rolling path 24 consisting of the female screw groove 14 and the male screw groove 23. As a result, when the nut 10 rotates, the balls 30 roll. The screw shaft 20 then moves inside the cylindrical portion 11 in the first direction X1 or the second direction X2.

[0021] As shown in Figure 2, the screw shaft 20 includes a shaft mounting hole 25 that penetrates the first end face 21 and the second end face 22, a first housing groove 26 formed by recessing a part of the first end face 21, a second housing groove 27 formed by recessing a part of the second end face 22, and a return passage 28 that penetrates in the direction of the axis X.

[0022] The shaft mounting hole 25 is a circular hole centered on axis X. Therefore, as shown in Figure 3, the shaft mounting hole 25 is located in the center of the second end face 22. Similarly, as shown in Figure 4, the shaft mounting hole 25 is located in the center of the first end face 21.

[0023] The first and second storage grooves 26 and 27 are grooves for accommodating common circulating components 40 and share a common configuration. Therefore, the common configuration will be explained using the second storage groove 27 as a representative example. The first storage groove 26 will be explained by listing only the differences from the second storage groove 27.

[0024] As shown in Figure 2, the depth of the second housing groove 27, in other words, the length from the second end face 22 to the bottom surface 27a of the second housing groove 27, is L1. As shown in Figure 5, the second housing groove 27 is located radially outward from the shaft mounting hole 25. The second housing groove 27 has an arc shape when viewed from the axial X direction and has the same shape as the circulating component 40. On the bottom surface 27a of the second housing groove 27, there is a female screw hole 26b, a return passage 28, and a fitting portion 29. The female screw hole 26b is a hole into which a screw 32 for fixing the circulating component 40 is screwed.

[0025] The return passage 28 penetrates the bottom surface 26a of the first housing groove 26 and the bottom surface 27a of the second housing groove 27. As shown in Figure 5, the return passage 28 is located on the bottom surface 27a of the second housing groove 27, near the end in the counterclockwise direction (arrow A direction) when viewed from the motor 101. The female screw hole 26b is located on the bottom surface 27a of the second housing groove 27, near the end in the clockwise direction (arrow B direction) when viewed from the motor 101. Hereafter, the counterclockwise and clockwise directions will be based on the view from the motor 101. The fitting portion 29 is a circular recess that is concentric with the return passage 28 and has a larger diameter than the return passage 28.

[0026] As shown in Figure 4, the first accommodating groove 26 is offset approximately 90 degrees counterclockwise (in the direction of arrow A) relative to the second accommodating groove 27. Therefore, the return passage 28 is located near the end in the clockwise direction (in the direction of arrow B) on the bottom surface 26a of the first accommodating groove 26. Also, the female screw hole (not shown in Figure 4) into which the screw 32 is threaded is located near the end in the counterclockwise direction (in the direction of arrow A) on the bottom surface 26a of the first accommodating groove 26.

[0027] The circulating component 40 is a resin component. The same circulating component 40 is housed in the first housing groove 26 and the second housing groove 27. As shown in Figures 6 and 7, the circulating component 40 comprises an arc-shaped main body portion 41 housed in the first housing groove 26 or the second housing groove 27, and a bulging portion 42 that bulges radially outward from the outer circumferential surface 41a of the main body portion 41.

[0028] The main body 41 has a recessed portion of its outer circumferential surface 41a, a concave surface 43 that is continuous with the male screw groove 23 of the screw shaft 20, a radial passage 44 that guides the ball 30 radially inward from the concave surface 43, and an axial passage 45 that is continuous with the radial passage 44 and guides the ball 30 in the axial X direction. The radial passage 44 is a straight passage. The radial passage 44 is positioned gradually radially inward as it moves from the concave surface 43 toward the axial passage 45.

[0029] The main body portion 41 is provided with a hole 47 that penetrates in the axial direction X. As shown in Figures 3 and 4, the main body portion 41 is fastened and secured by a screw 32 that is inserted into the hole 47 and screwed into the female screw hole 26b.

[0030] As shown in Figure 7, the main body portion 41 has a contact surface 41b that abuts against the bottom surface 26a of the first housing groove 26 (see Figure 2) or the bottom surface 27a of the second housing groove 27 (see Figure 2). The main body portion 41 has a projection 48 that protrudes from the contact surface 41b. The projection 48 is inserted into the fitting portion 29 (see Figure 5), and the projection 48 is fitted into the fitting portion 29. The axial passage 45 passes through the inside of the projection 48.

[0031] As shown in Figure 7, the bulging portion 42 has an arc shape when cut in the direction of the axis X. The bulging portion 42 is located radially outward of the concave surface 43 and has a scooping portion 46 facing the concave surface 43. As shown in Figures 3 and 4, the bulging portion 42 fits into the female screw groove 14 of the nut 10. The scooping portion 46 is designed to scoop up the balls 30 on the rolling path 24 radially inward with its inner circumferential surface 46a. As shown in Figure 2, the thickness L2 in the direction of the axis X of the main body portion 41 of the circulating part 40 is smaller than the depth L1 of the second housing groove 27. Therefore, the circulating part 40 does not protrude beyond the second end face 22 in the second direction X2. Similarly, the circulating part 40 does not protrude beyond the first end face 21 in the first direction X1.

[0032] As shown in Figure 1, the shaft 110 is a cylindrical solid component. The shaft 110 has a first end face 111 facing a first direction and a second end face 112 facing a second direction. The first end face 111 has a connecting portion 113 that protrudes in the first direction X1. The connecting portion 113 is a part for connecting to a power transmission component. The connecting portion 113 is provided with a male threaded portion 113a for screwing on a nut (not shown) for tightening an object.

[0033] As shown in Figure 2, the second end face 112 has a cylindrical fixing portion 114 that protrudes in the second direction X2. The fixing portion 114 has a male threaded portion 115 at its end in the second direction X2. The fixing portion 114 is inserted into the shaft mounting hole 25 of the screw shaft 20. The male threaded portion 115 protrudes in the second direction X2 beyond the second end face 22 of the screw shaft 20. A shaft mounting nut 120 is screwed onto the male threaded portion 115. Thus, the screw shaft 20 is fastened to the shaft mounting nut 120 and the second end face 112 of the shaft 110, connecting the shaft 110.

[0034] Here, since the circulating parts 40, 40 are located inward in the axial X direction from the first end face 21 and the second end face 22, they are not subjected to tightening loads from the shaft mounting nut 120 and the second end face 112 of the shaft 110. Therefore, damage to the circulating parts 40, 40 is avoided. Furthermore, according to this embodiment, since the resin circulating parts 40 are not interposed between the screw shaft 20 and the shaft 110, or between the screw shaft 20 and the shaft mounting nut, the fixing strength of the shaft 110 to the screw shaft 20 is high.

[0035] Next, the effects of Embodiment 1 will be explained by giving a comparative example. As shown in Figures 8 and 9, the comparative example is a circulating type ball screw device 201 employing a ball 210, which circulates the ball 240 in one lead. The inner circumferential surface of the ball 210 has a return passage 211 for returning the ball 240 to the adjacent rolling path 225, and a pair of wall portions 212, 212 that sandwich the return passage 211.

[0036] The pair of wall sections 212, 212 need to have sufficient strength to guide the ball 240, and are designed to have thickness in a direction perpendicular to the return passage 211, in other words, roughly in the axial X direction. When the ball 210 is assembled to the ball screw device 201, as shown in Figure 9, a portion of the ball 210 protrudes into the adjacent rolling passage 225. As a result, as shown in Figure 9, there are rolling passages 225 that cannot be filled with balls 240, and the number of balls 240 that can be filled is reduced.

[0037] From the above, when using the 210 balls, the number of balls to be filled is reduced, and the load capacity is reduced. On the other hand, the ball screw device 1 of Embodiment 1 is designed so that there are no rolling paths 225 in which the balls 240 cannot be filled. Therefore, it has the effect of having a large number of balls 240 and a large load capacity.

[0038] As described above, the ball screw device 1 of Embodiment 1 comprises a screw shaft 20 having a nut 10 having an internal screw groove 14, an internal screw groove 23, and a return passage 28 extending in a direction parallel to the axis X of the nut 10, a plurality of balls 30 arranged in a rolling path 24 consisting of the internal screw groove 14 and the internal screw groove 23, and a plurality of circulating parts 40, 40 connecting the rolling path 24 and the return passage. The screw shaft 20 has a shaft mounting hole 25 that penetrates the center of both end faces of the screw shaft 20, and a first housing groove 26 and a second housing groove 27 that are recessed in a part of both end faces of the screw shaft 20 and located radially outward from the shaft mounting hole 25. The return passage 28 penetrates a part of the wall portion of the screw shaft 20 located between the bottom surface 26a of the first housing groove 26 and the bottom surface 27a of the second housing groove 27. Multiple circulating components 40, 40 are housed in the first housing groove 26 and the second housing groove 27.

[0039] The circulating parts 40, 40 are housed in the first housing groove 26 and the second housing groove 27, and are not subjected to the tightening load of the shaft mounting nut 120 and the shaft 110. Therefore, the circulating parts 40, 40 are not damaged. Since the circulating parts 40, 40 are not interposed between the shaft 110 and the screw shaft 20, the fixing strength of the shaft 110 to the screw shaft 20 is high.

[0040] Although Embodiment 1 has been described above, the present invention is not limited to the example described in the embodiment. For example, the thickness L2 of the circulating part 40 in the axial X direction may be the same as the depth L1 of the first housing groove 26 and the second housing groove 27. In such an example, the circulating part 40 does not protrude outward in the axial X direction from the first end face 21 and the second end face 22 and is not subjected to the tightening load of the nut and shaft. Therefore, the circulating part 40 is not damaged.

[0041] (Embodiment 2) Figure 10 is a side view of the actuator of Embodiment 2. Figure 11 is an enlarged view of the screw shaft and its vicinity in Embodiment 2. Figure 12 is a view of the second end face of the screw shaft as seen from the motor side. As shown in Figure 10, the actuator 100A of Embodiment 2 differs from the actuator 100 of Embodiment 1 in that it has a screw shaft 20A instead of the screw shaft 20. The differences will be explained below in detail.

[0042] As shown in Figure 11, the screw shaft 20A has ventilation holes 35 that penetrate in the axial X direction. Three ventilation holes 35 are provided. The ventilation holes 35 penetrate both end faces of the screw shaft 20A. As shown in Figure 12, on the second end face 22, the ventilation holes 35 are offset circumferentially from the second housing groove 27. Although not specifically shown, on the first end face 21, the ventilation holes 35 are also offset circumferentially from the first housing groove 26. The ventilation holes 35 are located radially outward from the shaft mounting nut 120 and the shaft 110 (see Figure 11). Therefore, they are not blocked by the shaft mounting nut 120 or the shaft 110.

[0043] From the above, the actuator 100A of Embodiment 2 comprises a ball screw device 1A, a shaft 110 in which a portion is inserted into a shaft mounting hole 25, a shaft mounting nut 120 for fastening the shaft 110, a motor 101 having an output shaft 101a, and a sealing member 16. The shaft mounting nut 120 is a bottomed cylindrical shape with an opening 15 at one end for incorporating a screw shaft 20A. The sealing member 16 closes the opening 15. The shaft 110 extends outside the nut 10, passing through the sealing member 16. One of the nut 10 and shaft 110 is connected to the output shaft 101a and rotates when driven by the output shaft 101a. The other of the nut 10 and shaft 110 moves in the axial X direction when driven by the output shaft 101a. The screw shaft 20A has ventilation holes 35 that pass through both end faces.

[0044] According to Embodiment 2, when the nut 10 rotates due to the drive of the output shaft 101a and the screw shaft 20A moves in the second direction X2, the air between the screw shaft 20A and the cover 12 is compressed by the screw shaft 20. Therefore, the compressed air passes through the vent hole 35 and moves into the space between the screw shaft 20A and the seal member 36. In other words, even when the screw shaft 20A moves in the second direction X2, the space between the screw shaft 20A and the seal member 36 expands and the air pressure does not decrease. As a result, foreign matter is not sucked in through the gap between the seal member 16 and the shaft 110.

[0045] On the other hand, when the screw shaft 20A moves in the first direction X1, the air between the screw shaft 20A and the sealing member 36 is compressed. Therefore, the compressed air passes through the vent hole 35 and moves into the space between the screw shaft 20A and the cover 12. As a result, the air pressure between the screw shaft 20A and the sealing member 36 does not increase. This prevents the air pressure between the screw shaft 20A and the sealing member 36 from increasing and causing the sealing member 16 to detach in the first direction X1.

[0046] (Embodiment 3) Figure 13 is a side view of the actuator of Embodiment 3. Figure 14 is a view of the screw shaft of Embodiment 3 from the lid side. Figure 15 is a view of the screw shaft of Embodiment 3 from the seal member side. The actuator 100B of Embodiment 3 differs from the actuator 100 of Embodiment 1 in that the ball screw device 1B has a multi-start screw structure. The differences will be explained below.

[0047] As shown in Figure 13, the inner circumferential surface of the cylindrical portion 11B of the nut 10B is provided with two female screw grooves 14A and 14B. The outer circumferential surface of the screw shaft 20B is provided with two male screw grooves 23A and 23B corresponding to the female screw grooves 14A and 14B. A ball 30A is arranged in the rolling path 24A, which consists of the female screw groove 14A and the male screw groove 23A. A ball 30B is arranged in the rolling path 24B, which consists of the female screw groove 14B and the male screw groove 23B. From the above, the ball screw device 1B of Embodiment 3 has a double-thread structure.

[0048] As shown in Figure 14, the screw shaft 20B has two return passages 28A and 28B. The screw shaft 20B also has two second housing grooves 27A and 27B formed by recessing the second end face 22. The second housing grooves 27A and 27B are positioned circumferentially offset by 180 degrees around the axis X. The second housing groove 27A houses a circulation device 40A that sends balls 30A rolling in the rolling passage 24A to the return passage 28A. The second housing groove 27B houses a circulation device 40B that sends balls 30B rolling in the rolling passage 24B to the return passage 28B. The return passages 28A and 28B are positioned circumferentially offset by 180 degrees around the axis X. The return passage 28A penetrates the bottom surface of the second housing groove 27A. The return passage 28B penetrates the bottom surface of the second storage groove 27B.

[0049] As shown in Figure 15, the screw shaft 20B has two first housing grooves 26A and 26B formed by recessing the first end face 21. The first housing groove 26A is offset approximately 90 degrees counterclockwise (in the direction of arrow A) from the second housing groove 27A. The first housing groove 26B is offset approximately 90 degrees counterclockwise (in the direction of arrow A) from the second housing groove 27B. The first housing groove 26A houses a circulation device 40A that sends the balls 30A rolling in the rolling path 24A to the return passage 28A. The first housing groove 26B houses a circulation device 40B that sends the balls 30B rolling in the rolling path 24B to the return passage 28B. The return passage 28A penetrates the bottom surface of the first housing groove 26A. The return passage 28B penetrates the bottom surface of the first housing groove 26B.

[0050] As described above, the ball screw device 1B of Embodiment 3 has a multi-start screw structure in which the nut 10B and screw shaft 20B have a plurality of female screw grooves 14A, 14B and a plurality of male screw grooves 23A, 23B. The screw shaft 20B has a plurality of first housing grooves 26A, 26B arranged circumferentially apart from each other, a plurality of second housing grooves 27A, 27B arranged circumferentially apart from each other, and a plurality of return passages 28A, 28B arranged circumferentially apart from each other.

[0051] According to the above configuration, the number of threads is increased compared to the ball screw device 1 of Embodiment 1, and therefore the load capacity of the ball screw device 1B is larger. Although Embodiment 3 shows a two-thread case as an example of a multi-thread screw structure, the present invention may also be a screw structure with three or more threads, and is not particularly limited.

[0052] (Embodiment 4) Figure 16 is a side view of the actuator of Embodiment 4. Embodiments 1 to 3 show examples in which nuts 10 and 10B are connected to the output shaft 101a of the motor 101, but the ball screw device of the present invention is not limited to this. Embodiment 4 describes an actuator 100C in which the shaft 110C is connected to the output shaft 101a of the motor 101.

[0053] The actuator 100C of Embodiment 4 comprises a motor 101, a ball screw device 1C, a shaft 110C, and a shaft mounting nut 120.

[0054] The ball screw device 1C differs from the ball screw device 1 of Embodiment 1 in that it is equipped with a nut 10C instead of a nut 10. Therefore, in the ball screw device 1C, the screw shaft 20, the plurality of balls 30 arranged between the nut 10 and the screw shaft 20, and the two circulating parts (not shown) provided on the first end face 21 and the second end face 22 of the screw shaft 20 are the same as those in the ball screw device 1 of Embodiment 1, and their description is omitted.

[0055] The nut 10C is a bottomed cylindrical component having a cylindrical portion 11C that forms a cylindrical shape around an axis X, and a cap portion 12C that closes the end of the cylindrical portion 11 in a first direction X1. A single female screw groove 14 is provided on the inner circumferential surface of the cylindrical portion 11. An opening 15C is provided at the end of the cylindrical portion 11 in a second direction X2. A sealing member 16C is provided in the opening 15C of the cylindrical portion 11C. A screw hole 17 is provided in the cap portion 12C. An eyebolt 18 for connecting to a power transmission component is screwed into the screw hole 17.

[0056] The shaft 110C has a fixing portion 114 that protrudes from its first end face 111 in a first direction X1 and is inserted into the shaft mounting hole 25 of the screw shaft 20. The end of the fixing portion 114 in the first direction X1 protrudes further in the first direction X1 than the first end face 21 of the screw shaft 20, and a shaft mounting nut 120 is screwed onto it. The first end face 111 of the shaft 110C and the shaft mounting nut 120 then tighten the screw shaft 20, making the shaft 110C and the screw shaft 20 a single unit.

[0057] Furthermore, the shaft 110C passes through the seal member 16C, and the second end face 112 of the shaft 110C is located outside the cylindrical portion 11C of the nut 10. The shaft 110C has a shaft portion 117 that protrudes in the second direction X2 from the second end face 112 and is supported by the bearing device 2. A bearing device nut 13b is screwed onto the shaft portion 117. The inner rings of the two rows of bearings 3, 3 are tightened by the bearing device nut 13b and the second end face 112. This applies preload to the inner rings of the two rows of bearings 3, 3. A connecting hole 117a is provided on the end face of the shaft portion 117. The output shaft 101a is fitted into the connecting hole 117a, and the shaft 110C and the output shaft 101a are integrated.

[0058] As described above, with the actuator 100C of Embodiment 4, when the motor 101 is started and the output shaft 101a is driven, the shaft 110C rotates around axis X. Then the ball 30 rolls, and the nut 10C moves in the first direction X1 or the second direction X2. As a result, the object connected to the eyebolt 18 can be moved. [Explanation of Symbols]

[0059] 1, 1B, 1C Ball screw device 2 Bearing device 10, 10B nuts 11, 11C Cylindrical section 12, 12C Lid 13. Shaft 14, 14A, 14B Female thread grooves 15, 15C opening 16, 16C sealing member 18 Eyebolts 20, 20A screw shaft 21 First end surface 22 Second end face 23, 23A, 23B Male thread groove 24, 24A, 24B rolling track 25 shaft mounting holes 26, 26A, 26B First housing groove 26a Bottom 27, 27A, 27B Second storage groove 27a Bottom 28, 28A, 28B Return passage 30 balls 32 screws 35 ventilation holes 40 Circulation Parts 41 Main body 42 Bulge 43 Concave 44 Radial passage 45 Axial passage 46. ​​Rescue Department 100, 100A, 100B, 100C actuators 101 Motor 110, 110C shaft 111 First end face 112 Second end face 120 Shaft mounting nut 201 Ball screw device 210 pieces 211 Return passage 212 Wall section

Claims

1. A nut having a female thread groove, A screw shaft having a male screw groove and a return passage extending in an axial direction parallel to the axis of the nut, A plurality of balls arranged in a rolling path consisting of the female screw groove and the male screw groove, Multiple circulating components connecting the aforementioned rolling path and return passage, Equipped with, The aforementioned screw shaft is A shaft mounting hole formed by penetrating the center of both end faces of the screw shaft, The screw shaft has a portion of both end faces recessed and a first and second housing groove located radially outward from the shaft mounting hole, It has, The return passage is formed by passing through a portion of the wall portion of the screw shaft located between the bottom surface of the first housing groove and the bottom surface of the second housing groove. Multiple of the aforementioned circulating components are housed in the first housing groove and the second housing groove, A portion of both end faces of the screw shaft is a tightening region that is tightened in the axial direction. The aforementioned tightening region is tightened in the axial direction by the shaft inserted into the shaft mounting hole and the shaft mounting nut that fastens the shaft. A portion of the clamping area overlaps with the first and second housing grooves in the axial direction. The axial thickness of the circulating component housed in the first housing groove is less than or equal to the axial depth of the first housing groove. The axial thickness of the circulating component housed in the second housing groove is less than or equal to the axial depth of the second housing groove. Ball screw device.

2. The nut and the screw shaft have a multi-start screw structure having a plurality of female screw grooves and a plurality of male screw grooves, The aforementioned screw shaft is A plurality of the first receiving grooves are arranged to be spaced apart from each other in the circumferential direction, A plurality of the second accommodating grooves are arranged to be spaced apart from each other in the circumferential direction, A plurality of return passages arranged to be spaced apart from each other in the circumferential direction, has The ball screw device according to claim 1.

3. A ball screw device comprising a screw shaft having a shaft mounting hole formed therein, A shaft, part of which is inserted into the shaft mounting hole, A shaft mounting nut for fastening the aforementioned shaft, A motor having an output shaft, sealing member and Equipped with, The aforementioned ball screw device is A nut having a female thread groove, The screw shaft having a male screw groove and a return passage extending in an axial direction parallel to the axis of the nut, A plurality of balls arranged in a rolling path consisting of the female screw groove and the male screw groove, Multiple circulating components connecting the aforementioned rolling path and return passage, Equipped with, The aforementioned screw shaft is The shaft mounting hole is formed by penetrating the center of both end faces of the screw shaft, The screw shaft has a portion of both end faces recessed and a first and second housing groove located radially outward from the shaft mounting hole, It has, The return passage is formed by passing through a portion of the wall portion of the screw shaft located between the bottom surface of the first housing groove and the bottom surface of the second housing groove. Multiple of the aforementioned circulating components are housed in the first housing groove and the second housing groove, The nut has a bottomed cylindrical shape with an opening at one end for incorporating the screw shaft, The sealing member closes the opening, The shaft extends through the sealing member and outward from the nut. One of the nut and the shaft is connected to the output shaft and rotates by the drive of the output shaft. The other of the nut and the shaft moves in the axial direction by the drive of the output shaft. The screw shaft has ventilation holes that penetrate both end faces. Actuator.

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