Ball screw device

Abstract

To provide a ball screw device capable of maintaining a satisfactory rolling state of a ball for a long time by preventing the ball, which rolls inside of a non-load passage, from being in contact with a corner of a nut member which is exposed in the passage.SOLUTION: A nut member comprises: a nut main body which includes a pair of ball circulation holes penetrating in a radial direction corresponding to both ends of a load passage and in which a ball return groove is formed between the pair of ball circulation holes; a pair of circulation members which is mounted in the pair of ball circulation holes of the nut main body and in which a first direction conversion groove is formed; and a lid member which is mounted to the nut main body to cover the ball return groove and the pair of circulation members, includes a guide groove constituting the return passage while overlapping the ball return groove and includes a second direction conversion groove which constitutes a direction conversion path while overlapping the first direction conversion groove of the circulation members continuously from the guide groove. A groove width of the ball return groove is set larger than a groove width of the guide groove.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a ball screw device capable of converting rotary motion into linear motion and vice versa. [Background technology]

[0002] Ball screw devices are mechanical elements capable of converting rotational motion and linear motion, and are widely used in various machine tools, conveying devices, industrial robots, etc. to convert rotational motion generated by servo motors into linear motion. Ball screw devices consist of a screw shaft and a cylindrical nut member threadedly engaged with each other via a large number of balls. The outer circumferential surface of the screw shaft is formed with a spiral rolling groove with a predetermined lead, along which the balls roll. Therefore, when the screw shaft is rotated once, the nut member moves in the axial direction of the screw shaft by the lead of the rolling groove. Therefore, for a given number of rotations applied to the screw shaft, the greater the lead of the rolling groove, the faster the nut member moves in the axial direction of the screw shaft.

[0003] The nut member has an infinite circulation path formed therein in which the numerous balls are arranged. This infinite circulation path is composed of a spiral load path in which the balls roll while bearing a load between the screw shaft and the nut member, and an unload path that connects both ends of the load path and in which the balls roll in a released state. The balls roll in the infinite circulation path as the screw shaft and the nut member rotate relative to each other.

[0004] In conventional ball screw devices, many different structures for the unloaded passage in the nut member have been proposed, and for example, the larger the lead of the rolling groove, the greater the movement of the ball in the axial direction of the nut member within the unloaded passage is required when returning the ball from the end to the start of the spirally formed loaded passage.

[0005] A ball screw device having such an unloaded passage is disclosed in Literature 1. In the ball screw device disclosed in Literature 1, the unloaded passage is constructed by attaching a pair of circulation pieces and a return passage member that connects the circulation pieces to each other to a nut member. The pair of circulation pieces have connecting passages that allow balls that have finished rolling in the loaded passage to leave the rolling grooves of the screw shaft, releasing the balls from the load and guiding them from the inside to the outside of the nut member. Meanwhile, the return passage member has a linear return passage that connects the pair of circulation pieces and extends in the axial direction of the nut member. By attaching the return passage member to the nut member, the connecting passage of the circulation pieces and the return passage are joined, completing the unloaded passage. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2017-137953 Summary of the Invention [Problem to be solved by the invention]

[0007] In a ball screw device with a large rolling groove lead, the unloaded path for the balls is constructed by attaching a pair of circulation pieces and a return path member to the nut member. In this case, the connection parts of the members are exposed in the unloaded path, and if there are any steps at these connection parts, this will hinder the smooth circulation of the balls in the unloaded path.

[0008] In particular, since the balls bear a load between the screw shaft and the nut member, the nut member is usually made of a metal material such as bearing steel, etc. Therefore, if a step occurs at the connection between the nut member and the circulation piece or the return passage member, there is a concern that the balls rolling in the no-load passage will come into contact with the corners of the metal nut member at the connection, causing abnormal wear on the surface of the balls. [Means for solving the problem]

[0009] The present invention has been made in consideration of these problems, and its object is to provide a ball screw device that, when combining multiple components to form an unloaded ball passage for a nut member, prevents the balls rolling in the unloaded passage from contacting the corners of the nut member that are exposed in the passage, and can maintain a good rolling state of the balls for a long period of time.

[0010] The ball screw device of the present invention includes a large number of balls, a screw shaft having a spirally formed rolling groove for the balls on its outer circumferential surface, and a nut member having a through hole through which the screw shaft is inserted and which threadably engages with the screw shaft via the large number of balls and which has an infinite circulation path for the large number of balls. The infinite circulation path is composed of a load passage through which the large number of balls roll spirally between the screw shaft and the nut member, a pair of direction change passages located at both ends of the load passage, and a return passage connecting the pair of direction change passages. The nut member has the through hole, and the load passage is formed between it and the screw shaft. It has a pair of ball circulation holes that penetrate radially corresponding to both ends of the load passage, and further comprises: a nut body having a ball return groove formed on its outer surface between the pair of ball circulation holes; a pair of circulation members that are attached to the pair of ball circulation holes of the nut body and have a first direction change groove formed therein; and a cover member that is attached to the nut body to cover the ball return groove and the pair of circulation members, has a guide groove that overlaps with the ball return groove to form the return passage, and has a second direction change groove that continues from the guide groove and overlaps with the first direction change groove of the circulation member to form the direction change path.

[0011] As a first feature, the groove width of the ball return groove is set to be larger than the groove width of the guide groove.

[0012] As a second feature, the depth of the ball return groove is set to be greater than the depth of the first direction change groove. [Effects of the Invention]

[0013] According to the present invention, when a plurality of components are combined to construct an unloaded passage for the ball relative to the nut component, it is possible to prevent the corners of the nut component from protruding as steps into the unloaded passage, thereby preventing scratches from occurring on the surface of the ball and enabling the ball to maintain a good rolling condition for a long period of time. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing an example of a ball screw device to which the present invention is applied; [Figure 2] FIG. 4 is an enlarged perspective view showing a state in which a circulation member is attached to a nut body. [Figure 3] FIG. 2 is a perspective view showing the front surface side of the circulation member. [Figure 4] FIG. 4 is a perspective view showing the rear side of the circulation member. [Figure 5] FIG. [Figure 6] FIG. 4 is an enlarged perspective view showing a connection portion between a ball circulation hole and a ball return groove of the nut body. [Figure 7] 10 is a perspective view showing a connection state between a direction change path and a return path provided in the nut member. FIG. [Figure 8] 10 is a diagram showing a cross section of a direction change path formed by overlapping a circulation member and a cover member. FIG. [Figure 9] 10 is a view showing a cross section of a return passage formed by overlapping the nut body and the cover member. FIG. [Figure 10] 10 is a cross-sectional view of the connection between the direction change path and the return path, observed from a direction perpendicular to the rolling direction of the balls. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] The ball screw device of the present invention will be described in detail below with reference to the accompanying drawings.

[0016] Fig. 1 shows an example of a ball screw device to which the present invention is applied. This ball screw device 1 is composed of a screw shaft 2 having a ball rolling groove 20 formed helically on its outer circumferential surface, and a cylindrical nut member 3 that threads onto the periphery of the screw shaft 20 via a large number of balls 5. The nut member 3 also has an infinite circulation path for the balls. The balls 5 are interposed between the screw shaft 2 and the nut member 3, and for example, by rotating the screw shaft 2 relative to the nut member 3, the nut member 3 moves in the axial direction of the screw shaft 2, or by rotating the nut member 3 relative to the screw shaft 2, the screw shaft 2 moves in the axial direction of the nut member 3.

[0017] A single rolling groove 20 is formed on the outer peripheral surface of the screw shaft 2 with a predetermined lead, and the rolling groove 20 exists at a constant pitch along the axial direction of the screw shaft 2. A thread portion 21 is formed between adjacent rolling grooves 20, and the thread portion 21 indicates the outer diameter of the screw shaft 2. In this embodiment, the lead of the rolling groove 20 is set larger than the outer diameter of the screw shaft 2.

[0018] The nut member 3 is formed in a cylindrical shape and has a through hole through which the screw shaft 2 is inserted. A spiral load rolling groove having the same lead as the rolling groove 20 of the screw shaft 2 is formed on the inner peripheral surface of the nut member 3. The balls 5 roll between the rolling groove of the screw shaft and the load rolling groove of the nut member, and a load is applied between the screw shaft 2 and the nut member 3.

[0019] The nut member 3 has a cylindrical shape with no irregularities on its outer circumferential surface. The nut member 3 is composed of a metal nut body 30 having the through hole and the load rolling groove formed on the inner circumferential surface of the through hole, a pair of circulation members 31 attached to the nut body 30, and a cover member 32 fixed to the nut body 30 so as to cover the pair of circulation members 31. The rolling grooves 20 of the screw shaft 2 and the load rolling grooves of the nut body 30 face each other to form a load passage for balls 5, and the balls 5 roll spirally within the load passage while bearing the load acting between the screw shaft 2 and the nut member 3.

[0020] The pair of circulation members 31 and the cover member 32 are made of synthetic resin, and by attaching the pair of circulation members 31 and the cover member 32 to the nut body 30, an unloaded passage 50 is formed in the nut member 3, in which the balls 5 roll when released from the load, and both ends of the loaded passage are connected by the unloaded passage. Note that Figure 1 shows a state in which the cover member 32 has been removed from the nut body 30, exposing the unloaded passage 50 for the balls 5.

[0021] The nut body 30 has a flat mounting surface 34 formed by cutting out a portion of the outer circumferential surface, and the nut member 3 is cylindrical when the cover member 32 is fixed to this mounting surface 34. A ball return groove extending linearly in the axial direction of the nut body 30 is formed in the mounting surface 34 of the nut body 30, and constitutes part of the no-load passage 50. The mounting surface 34 also has a pair of ball circulation holes into which the pair of circulation members 31 respectively fit. The pair of ball circulation holes are located at both ends of the ball return groove.

[0022] 2 is an enlarged perspective view showing the state in which the circulation member 31 is attached to the ball circulation hole. The ball circulation hole 35 penetrates the nut body 30 in the radial direction and is provided at a position corresponding to an end of the load rolling groove formed on the inner circumferential surface of the nut body 30. The circulation member 31 is provided with a first direction change groove 40, and when the circulation member 31 is attached to the ball circulation hole 35 of the nut body 30, one end of the first direction change groove 40 is connected to the ball return groove 36.

[0023] The ball return groove 36 has a rectangular cross section perpendicular to its longitudinal direction, and the depth of the ball return groove 36 is the same as or slightly deeper than the radius of the ball 5. The width of the ball return groove 36 is set slightly larger than the diameter of the ball 5.

[0024] 3 and 4 are views showing the circulation member 31, with FIG. 3 being a view of the front side of the circulation member, i.e., the circulation member 31 observed from the radially outer side of the nut member 3, and FIG. 4 being a view of the back side of the circulation member 31, i.e., the circulation member 31 observed from the radially inner side of the nut member 3. The circulation member 31 is composed of a guide portion 310 positioned to close the end of the load rolling groove, and a fitting portion 311 provided to protrude around the guide portion 310 and contribute to fixing the circulation member 31 to the nut body 30. As shown in FIG. 3, the first direction changing groove 40 is formed across the guide portion 310 and the fitting portion 311. The cross section of the first direction changing groove 40 is formed in a semicircular shape that approximates the spherical surface of the ball 5, and the radius of the first direction changing groove 40 is set to be slightly larger than the radius of the ball 5.

[0025] A scooping portion 312 is provided at the end of the first direction changing groove 40 on the guide portion 310 side to transfer the balls 5 between the first direction changing groove 40 and the rolling groove 20 of the screw shaft 2. This scooping portion 312 is provided by cutting out the first direction changing groove 40 in a substantially U-shape. Also, as shown in FIG. 4, the guide portion 310 is provided with a protrusion 313 that fits into the rolling groove 20 of the screw shaft 2 while maintaining a gap. Therefore, as shown in FIG. 3, the scooping portion 312 has a substantially M-shape as a whole.

[0026] 5 shows the cover member 32 fixed to the nut body 30, and shows the back side of the cover member 32, i.e., the surface that comes into contact with the nut body 30. As shown in the figure, a guide groove 321 that corresponds to the ball return groove 36 of the nut body 30 is formed in the cover member 32. The cross section of this guide groove 321 perpendicular to its longitudinal direction is formed in a semicircle that approximates the spherical surface of the ball 5, and its radius is set slightly larger than the radius of the ball 5. When the cover member 32 is attached to the nut body 30, the guide groove 321 overlaps with the ball return groove 36 of the nut body 30 to form a ball return passage.

[0027] The cover member 32 is also provided with a pair of guide protrusions 322 located at both ends of the guide groove 321. When the cover member 32 is attached to the nut body 30, these guide protrusions 322 overlap the circulation member 31, fit into the ball circulation hole 35, and cover the circulation member 31. Each guide protrusion 322 is formed with a second direction change groove 323 continuing from the guide groove 321. Similar to the guide groove 321 and the first direction change groove 40 formed in the circulation member 31, the cross section of this second direction change groove 323 is formed in a semicircle approximating the spherical surface of the ball 5, and the radius of the second direction change groove 323 is set slightly larger than the radius of the ball 5. When the cover member 32 is attached to the nut body 30, the second direction change groove 323 overlaps with the first direction change groove 40 of the circulation member 31 and forms a direction change path that transfers the ball 5 between the load passage and the return passage.

[0028] The balls 5 rolling along the spiral loaded rolling path provided between the screw shaft 2 and the nut body 30 reach the ball circulation hole 35 of the nut body 30, enter the direction change path formed by the circulation member and the cover member, and are released from the load. The balls 5 also change their traveling direction by approximately 90 degrees within the direction change path, and are sent into the linear return path formed by the ball return groove 36 of the nut body 30 and the guide groove 321 of the cover member 32. The balls 5 rolling through the return path in an unloaded state are sent back into the spiral loaded rolling path via the direction change path on the opposite side. In this way, the balls 5 circulate endlessly inside the nut member 3.

[0029] 6 shows the connection between the ball circulation hole 35 and the ball return groove 36 formed in the nut body 30. A receiving portion 351 into which the fitting portion 311 of the circulation member 31 fits is provided around the ball circulation hole 35, and an end of the ball return groove 36 opens into the receiving portion 311.

[0030] 7 shows the state in which the circulation member 31 is attached to the ball circulation hole 35 and the cover member 32 is fixed to the attachment surface 34 of the nut body 30. However, the cover member 32 is partially cut away so that the connection state between the first direction change groove 40 of the circulation member 31 and the ball return groove 36 of the nut body 30 can be seen. As can be seen from this figure, the ball return groove 36 of the nut body 30 and the guide groove 321 of the cover member 32 overlap each other, forming the linear return passage 51 in which the balls 5 roll in an unloaded state, as described above. In addition, the first direction change path 40 of the circulation member 31 is continuous with the ball return groove 36 of the nut body 30, allowing the balls 5 to move back and forth between the ball return groove 36 and the first direction change path 40.

[0031] 8 is a cross-sectional view showing a direction change path 52 for a ball 5 formed by overlapping the first direction change groove 40 of the circulation member 31 and the second direction change groove 323 of the cover member 32. The cross sections of the first direction change groove 40 and the second direction change groove 323 are formed in a semicircular shape with the same inner diameter D1, which is set slightly larger than the diameter D0 of the ball 5. Therefore, the direction change path 52 is a passage with a circular cross section and an inner diameter D1 larger than the diameter D0 of the ball 5, and the ball 5 rolls inside the direction change path 52 in an unloaded state.

[0032] 9 is a cross-sectional view showing a return passage 51 for the ball 5 formed by overlapping the ball return groove 36 of the nut body and the guide groove 321 of the cover member 32. The cross section of the guide groove 321 is formed in a semicircular shape with an inner diameter D1, similar to the second direction change groove 323 that is continuous with the guide groove 321. Meanwhile, the ball return groove 36 facing the guide groove 321 is formed in a channel shape having a pair of side walls and a bottom surface, and the groove width of the ball return groove 36 is set to W1, which is slightly larger than the diameter D0 of the ball 5. Furthermore, the depth of the ball return groove 36 is set to H1, which is slightly larger than the diameter D0 / 2 of the ball 5. Therefore, the ball 5 rolls in an unloaded state inside the return passage 51 formed by overlapping the guide groove 321 and the ball return groove 36.

[0033] When the inner diameter D1 of the guide groove 321 is compared with the groove width W1 of the ball return groove 36, the groove width W1 of the ball return groove 36 is formed to be slightly larger than the inner diameter D1 of the guide groove 321. For this reason, within the return passage 51, the corner of the upper edge of the ball return groove 36, i.e., the corner where the mounting surface 34 of the nut body 30 and the side wall of the ball return groove 36 intersect, is slightly recessed with respect to the side edge of the guide groove 321 in the cover member 32, and the cover member 32 covers the corner of the upper edge of the ball return groove 36.

[0034] Because the ball return groove 36 is formed in the metal nut body 30, if the ball 5 rolling in the return passage 51 comes into contact with a corner at the upper end edge of the ball return groove 36, there is a concern that scratches will be generated on the surface of the ball 5, which may cause poor lubrication or abnormal wear of the ball 5. However, in the nut member 3 of this embodiment, the corner at the upper end edge of the ball return groove 36 is covered by the cover member 32, and the ball 5 rolling in the return passage 51 will not come into contact with the corner, making it possible to maintain a good rolling state of the ball 5 for a long period of time.

[0035] 10 is a cross-sectional view of the connection between the direction change path 52 and the return path 51, viewed from a direction perpendicular to the traveling direction of the balls 5. The direction change path 52 is configured such that the second direction change groove 323 of the cover member 32 and the first direction change groove 40 of the circulation member 31 face each other. The return path 51 is configured such that the guide groove 321 of the cover member 32 and the ball return groove 36 of the nut body face each other. As described above, the first direction change groove 40 is formed in a semicircular shape with an inner diameter D1, and the depth of the first direction change groove 40 shown in the figure is 1 / 2 of D1. On the other hand, the ball return groove 36 is formed in a channel shape, and its depth is H1.

[0036] When the depth of the first direction change groove 40 is compared with the depth of the ball return groove 36, the depth H1 of the ball return groove 36 is set to be slightly larger than the depth D1 / 2 of the first direction change groove 40. Therefore, when the circulation member 31 is fitted into the ball circulation hole 35 of the nut body 30 and the cover member 32 is fixed to the mounting surface 34 of the nut body 30 and the cover member 32 and the circulation member 31 are in contact with each other, the deepest part of the first direction change groove 40 is slightly higher than the bottom surface of the ball return groove 36, and a slight step is generated between the return passage 51 and the direction change path 52.

[0037] Because the ball return groove 36 is formed in the metal nut body 30, if the bottom surface of the ball return groove 36 were higher than the deepest part of the first direction change groove 40, there would be a concern that the ball 5 would collide with the edge of the ball return groove when entering the return passage 51 from the direction change passage 52, causing scratches on the surface of the ball 5. However, in the nut member 3 of this embodiment, the deepest part of the first direction change groove 40 is slightly higher than the bottom surface of the ball return groove 36, so the ball 5 will not collide with the edge of the ball return groove 36 when entering the return passage 51 from the direction change passage 52. On the other hand, there is a concern that the ball 5 will collide with the edge of the first direction change groove 40 when entering the direction change passage 52 from the return passage 51. However, because the circulation member 31 in which the first direction change groove 40 is formed is made of synthetic resin, it is possible to prevent scratches on the surface of the ball 5 from being caused by such a collision.

[0038] As described above, according to the ball screw device 1 of this embodiment, the groove width of the ball return groove 36 formed in the nut body 30 is set larger than the groove width of the guide groove 321 formed in the cover member 32, and further, the groove depth of the ball return groove 36 is set larger than the depth of the deepest part of the first direction change groove 40 formed in the circulation member 31. Therefore, when the balls 5 roll in the return passage 51 or enter and exit the direction change passage 52 from this return passage 51, they do not come into contact with the edge of the ball return groove formed in the metal nut body, so that the surface of the balls can be kept in good condition for a long period of time, and the balls can be maintained in a smooth circulation state in the endless circulation passage. [Explanation of symbols]

[0039] 1...ball screw device, 2...screw shaft, 3...nut member, 5...ball, 30...nut body, 31...circulation member, 32...lid member, 35...ball circulation hole, 36...ball return groove, 40...first direction change groove, 50...unloaded passage, 51...return passage, 52...direction change passage

Claims

1. Many balls and a screw shaft having a rolling groove for the balls formed in a spiral shape on an outer peripheral surface thereof; A nut member having a through hole through which the screw shaft is inserted, screwed onto the screw shaft via the plurality of balls, and having an infinite circulation path for the plurality of balls, The infinite circulation path is a load passage in which the large number of balls roll spirally between the screw shaft and the nut member; a pair of turning paths located at both ends of the load path; a return passage connecting the pair of direction change passages, The nut member is a nut body having the through hole, the load passage formed between the nut body and the screw shaft, a pair of ball circulation holes penetrating radially corresponding to both ends of the load passage, and a ball return groove formed on the outer circumferential surface between the pair of ball circulation holes; a pair of circulation members that are attached to the pair of ball circulation holes of the nut body and have first direction change grooves; a cover member that is attached to the nut body to cover the ball return groove and the pair of circulation members, the cover member having a guide groove that overlaps with the ball return groove to form the return passage, and a second direction change groove that continues from the guide groove and overlaps with the first direction change groove of the circulation member to form the direction change path, A ball screw device, characterized in that the groove width of the ball return groove is larger than the groove width of the guide groove.

2. 2. The ball screw device according to claim 1, wherein the depth of the ball return groove is set to be greater than the depth of the first direction change groove.

3. 3. The ball screw device according to claim 2, wherein the guide groove, the first direction change groove, and the second direction change groove are formed in a semicircular shape with an inner diameter larger than the diameter of the ball, while the ball return groove has a cross section perpendicular to its longitudinal direction that is rectangular.

4. Many balls and a screw shaft having a rolling groove for the balls formed in a spiral shape on an outer peripheral surface thereof; A nut member having a through hole through which the screw shaft is inserted, screwed onto the screw shaft via the plurality of balls, and having an infinite circulation path for the plurality of balls, The infinite circulation path is a load passage in which the large number of balls roll spirally between the screw shaft and the nut member; a pair of turning paths located at both ends of the load path; a return passage connecting the pair of direction change passages, The nut member is a nut body having the through hole, the load passage formed between the nut body and the screw shaft, a pair of ball circulation holes penetrating radially corresponding to both ends of the load passage, and a ball return groove formed on the outer circumferential surface between the pair of ball circulation holes; a pair of circulation members that are attached to the pair of ball circulation holes of the nut body and have first direction change grooves; a cover member that is attached to the nut body to cover the ball return groove and the pair of circulation members, the cover member having a guide groove that overlaps with the ball return groove to form the return passage, and a second direction change groove that continues from the guide groove and overlaps with the first direction change groove of the circulation member to form the direction change path, A ball screw device, characterized in that the depth of the ball return groove is set to be greater than the depth of the first direction change groove.

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