Ball screw nut inspection device and ball screw nut inspection method
Patent Information
- Application Number
- PCT/JP2026/006625
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-21
- Filing Date
- 2026-02-24
- Publication Date
- 2026-09-24
Smart Images
Figure JP2026006625_24092026_PF_FP_ABST
Abstract
Description
Apparatus for inspecting ball screw nut and method for inspecting ball screw nut
[0001] The present invention relates to an apparatus for inspecting a ball screw nut and a method for inspecting a ball screw nut.
[0002] In a ball screw device, a large number of balls are rollably disposed in a ball rolling path formed by a thread groove formed on an inner peripheral surface of a nut and a thread groove formed on an outer peripheral surface of a screw shaft. The balls that have reached the end point of the ball rolling path are returned to the start point of the ball rolling path via the ball circulation path.
[0003] Some ball circulation paths are formed on a member separate from the nut body (for example, a piece member). In this case, a nut having a ball rolling path and a ball circulation path is completed by fixing the piece member to the nut. On the other hand, in recent years, a ball screw device has also been proposed in which a circulation groove functioning as a ball circulation path is directly formed on the inner peripheral surface of the nut, thereby reducing cost compared to a case where the circulation groove is formed on a member separate from the nut (for example, Patent Document 1 below).
[0004] The ball screw nut manufacturing apparatus described in Patent Document 1 includes a cam slider having a convex portion for processing a circulation groove, and a cam driver for pressing the cam slider in a radial direction. The circulation groove can be formed on the inner peripheral surface of the nut by inserting the cam slider into the inner diameter of the nut blank and pushing in the cam driver.
[0005] Japanese Patent No. 6015444
[0006] When the circulation groove is formed by the method described in Patent Document 1, if the depth of the circulation groove is insufficient due to, for example, insufficient pushing of the cam driver, smooth ball circulation may be hindered when the ball screw device is operated. For this reason, it is important to ensure a sufficient depth of the circulation groove. On the other hand, if the depth of the circulation groove is too large, the balls tend to be arranged in a staggered manner inside the circulation groove, which may make it difficult for the balls to circulate. Therefore, an appropriate groove depth for the circulation groove has an upper limit value and a lower limit value, and by inspecting whether the groove depth is within the range from the lower limit value to the upper limit value, it can be inspected whether the circulation groove functions properly.
[0007] When inspecting the depth of a circulation groove, measuring the depth using a measuring terminal is difficult because the terminal cannot easily reach the bottom of the groove. While cutting the nut allows for measuring the groove depth using a measuring terminal, the cut nut cannot be used as a product. Therefore, a non-destructive inspection method is needed to determine whether the depth of the circulation groove formed on the inner circumference of the nut is greater than or equal to a predetermined depth.
[0008] Therefore, the present invention provides an inspection device for ball screw nuts and a method for inspecting ball screw nuts that can non-destructively inspect the depth of the circulation groove formed on the inner circumferential surface of the nut.
[0009] The present invention provides an inspection device for ball screw nuts, wherein a helical groove and a circulation groove that returns the ball from the end to the start of the helical groove are formed on the inner circumferential surface of the ball screw nut, and the device acquires relative depth information with respect to a specified depth of the circulation groove to inspect the depth of the circulation groove, comprising: a first member having a plurality of divided bodies inserted into the inside of the nut and arranged in the circumferential direction, each divided body having a projection on its outer circumferential surface that fits into the circulation groove; and a second member being inserted axially inward from the axial end of the first member, so that each divided body of the first member moves toward the outer diameter side and the projection fits into the circulation groove. Here, "specified depth" is the depth of the circulation groove arbitrarily specified for the nut to be inspected, and is predetermined for each inspection. "Relative depth information" refers to information on the depth compared to the specified depth, with respect to the specified depth as the reference. Specifically, this is information that the depth exceeds the specified depth (is deeper than the specified depth), is the same as the specified depth, or is less than the specified depth (is shallower than the specified depth).
[0010] The ball screw nut inspection device of the present invention comprises a first member and a second member. The first member has a plurality of segments, each provided with a projection that fits into a circulation groove, and each segment is movable in the radial direction. With the first member inserted inside the nut, the second member is fitted axially inward from the axial end of the first member, causing each segment to move outward so that the projections fit into the circulation groove. When the projections contact the bottom of the circulation groove, the axial movement of the second member is restricted. Therefore, relative depth information with respect to a specified depth of the circulation groove can be obtained from the axial position when the insertion of the second member is restricted, and the groove depth of the circulation groove can be inspected.
[0011] Specifically, a predetermined depth (an arbitrarily specified groove depth) of the circulation groove is set in advance. When the second member is inserted, if the projection of the first member contacts the second member at the predetermined depth (i.e., the movement of the second member is restricted), the axial position of the second member becomes the boundary position indicating that the circulation groove is the same depth as the predetermined depth. In other words, if the second member can be inserted up to the boundary position (the insertion of the second member is restricted at the boundary position), the projection will contact the circulation groove at the predetermined depth. Therefore, it can be seen that the depth of the circulation groove is the same as the predetermined depth. Also, if the second member can be inserted axially inward from the boundary position (the insertion of the second member is restricted axially inward from the boundary position), the projection will contact the circulation groove at a position deeper than the predetermined depth. Therefore, it can be seen that the depth of the circulation groove exceeds the predetermined depth. On the other hand, if the second member cannot be inserted up to the boundary position (the insertion of the second member is restricted axially outward from the boundary position), the projection will contact the circulation groove at a position shallower than the predetermined depth. Therefore, it can be seen that the depth of the circulation groove is less than the specified depth.
[0012] The specified depth can be the lower limit or upper limit of the allowable range of the circulation groove depth. The "allowable range of the circulation groove depth" is a range of groove depths that is considered preferable for the circulation groove of the nut to be inspected, and is predetermined. For example, it is considered from the viewpoint of groove depth that does not hinder the smooth rolling of the balls, and can be set in various ways depending on the ball diameter, the shape of the circulation groove, etc., and is set for each nut to be inspected.
[0013] By setting the specified depth to the upper limit of the allowable range, it is possible to obtain information on whether the depth of the circulation groove exceeds, is the same as, or falls below the upper limit, and to check whether the depth of the circulation groove is too deep. Conversely, by setting the specified depth to the lower limit of the allowable range, it is possible to obtain information on whether the depth of the circulation groove exceeds, is the same as, or falls below the lower limit, and to check whether the depth of the circulation groove is too shallow.
[0014] In the above configuration, a positioning member may be provided, which is inserted inside the nut and, with the projection of the first member and the circulation groove aligned in phase, restricts the axial movement and circumferential rotation of the first member, while allowing the radial movement of the first member.
[0015] In this case, it is preferable that a flange is provided at the axial end of the positioning member, with one axial end face of the flange contacting the nut and the other axial end face of the flange contacting the first member. Furthermore, it is preferable that each segment of the first member is provided with a radially projecting projection, and that a fitting recess is provided on the other axial end face of the flange into which the projection fits. With the positioning member configured in this way, the first member is positioned by the positioning member, making it easier for the projection to fit accurately into the circulation groove, thereby improving inspection accuracy and speeding up inspection.
[0016] In the above configuration, the inner diameter surface of the axial end of the first member is tapered, expanding in diameter from the axial inner side to the outer side, and the second member may also have a tapered surface. This allows the second member to fit smoothly into the interior of the first member, making it easier to inspect.
[0017] The present invention provides a method for inspecting a ball screw nut, which involves using a ball screw nut inspection device to insert the first member into the nut, aligning the phase of the projection of the first member with the phase of the circulation groove, inserting the second member axially inward from the axial end of the first member, moving each segment of the first member toward the outer diameter to engage the projection with the circulation groove, and, when the insertion of the second member into the first member is restricted, obtaining relative depth information from the axial position of the second member with respect to a specified depth of the circulation groove, thereby inspecting the depth of the circulation groove.
[0018] The ball screw nut inspection device and ball screw nut inspection method of the present invention make it possible to non-destructively inspect the depth of the circulation groove formed on the inner circumferential surface of the nut.
[0019] This is a cross-sectional view of a ball screw device. This is a perspective view of a ball screw nut inspection device and a ball screw nut. This is a front view from the direction of arrow A in Figure 2, with the positioning member and the first member inserted into the nut, before the second member is fitted. This is a cross-sectional view along the line B-B in Figure 3. This is a front view from the direction of arrow A in Figure 2, with the positioning member and the first member inserted into the nut, after the second member has been fitted. This is a cross-sectional view along the line C-C in Figure 5. This shows the allowable range of the depth of the circulation groove, and illustrates the case when the depth of the circulation groove is within the allowable range. This shows the allowable range of the depth of the circulation groove, and illustrates the case when the depth of the circulation groove is less than the lower limit of the allowable range. This shows the allowable range of the depth of the circulation groove, and illustrates the case when the depth of the circulation groove exceeds the upper limit of the allowable range. This shows a method for inspecting the depth of the circulation groove, and illustrates the case when the circulation groove is at the specified depth. This shows a method for inspecting the depth of the circulation groove, and illustrates the case when the circulation groove is deeper than the specified depth. This shows a method for inspecting the depth of the circulation groove, and illustrates the case when the circulation groove is less than the specified depth.
[0020] Embodiments of the present invention will be described below with reference to the drawings. First, the configuration of the ball screw device will be described. As shown in Figure 1, the ball screw device 101 mainly comprises a nut 102, a screw shaft 103, and a number of balls 104.
[0021] A rolling groove 120 is formed on the inner circumferential surface of the nut 102, on which the ball 104 rolls, and a rolling groove 130 is formed on the outer circumferential surface of the screw shaft 103, on which the ball 104 rolls. The rolling groove 120 on the inner circumferential surface of the nut 102 is composed of a helical groove 121 and a circulation groove 122 that connects the start and end of each helical groove 121. The groove depth of the circulation groove 122 is deeper than the groove depth of the helical groove 121. The circulation groove 122 connects the ends of the helical grooves 121 located on both sides of the axial direction of the screw thread 131 of the screw shaft 103. A spiral ball rolling path 106 is formed by the helical groove 121 of the nut 102 and the rolling groove 130 of the screw shaft 103, and a ball circulation path 107 is formed by the circulation groove 122 of the nut 102 and the outer circumferential surface of the screw shaft 103 (rolling groove 130 and screw thread 131). Multiple balls 104 are rotatably housed in the ball passage 108 formed by the ball rolling path 106 and the ball circulation path 107. The axial direction of the nut 102 refers to the direction along the axial direction in which the nut 102 extends.
[0022] In Figure 1, the cross-sectional shapes of the helical groove 121 and circulation groove 122 of the nut 102, and the rolling groove 130 of the screw shaft 103, are shown as an example where they are formed in an arc shape. However, these cross-sectional shapes may be other shapes, such as a Gothic arch shape.
[0023] By rotating the nut 102 and the screw shaft 103 relative to each other, it becomes possible to move the nut 102 and the screw shaft 103 relative to each other in the axial direction through the rolling of the balls 104 in the ball passage 108. The balls 104 that have rolled along the ball rolling path 106 and reached its end are scooped up and moved to the ball circulation path 107, where they cross the threads 131 of the screw shaft 103. After that, the balls 104 are returned from the ball circulation path 107 to the beginning of the ball rolling path 106. As a result, the balls 104 circulate indefinitely in the ball passage 108 while the nut 102 and the screw shaft 103 are rotating relative to each other.
[0024] As described above, the inner circumferential surface of the nut 102 has a plurality of helical grooves 121 and a plurality of circulation grooves 122 that connect the start and end of each helical groove 121. As an example of a nut to be inspected in this embodiment, a nut 102 provided with four circulation grooves 122a, 122b, 122c, and 122d will be described. In Figure 1, three circulation grooves 122a, 122c, and 122d are shown, and circulation groove 122b is omitted from the illustration. The circulation grooves 122a to 122d are arranged so that each has a different circumferential phase (in this embodiment, the phases are shifted by 90° at equal pitches) and different axial positions (122a, 122b, 122c, and 122d in order from the right in Figure 1). The circumferential direction of the nut 102 refers to the direction along the arc of the nut 102, which is configured in an arc shape.
[0025] Figure 2 shows a perspective view of the inspection device for a ball screw nut and the nut 102 to be inspected according to this embodiment. As shown in Figure 2, the nut 102 is provided with a projection-shaped engaging portion 109 that protrudes axially outward from one end face. The engaging portion 109 is provided in a circumferential region of one end face of the nut 102 and has an arc shape when viewed in the axial direction. Note that the axial outward side of the nut 102 is the outward side with respect to the axial center of the nut 102 (not shown), and means the side away from the axial center of the nut 102.
[0026] Next, the ball screw nut inspection device of this embodiment will be described with reference to Figures 2 to 7C. The ball screw nut inspection device of this embodiment acquires relative depth information of the circulation groove 122 with respect to a predetermined depth (specified depth, described later) of the nut 102, and inspects the depth of the circulation groove 122. As shown in Figure 2, the ball screw nut inspection device comprises a first member 1 inserted into the nut 102, a second member 10 inserted into the first member 1, and a positioning member 20 that enables the positioning of the first member 1.
[0027] The first member 1 has a plurality of divided bodies 2 arranged in the circumferential direction. In this embodiment, the first member 1 is composed of four divided bodies 2a, 2b, 2c, and 2d. As shown in Figures 2 and 4, each divided body 2 is composed of a main body portion 3 that extends in the axial direction and has an arc shape with a curvature approximately the same as that of the nut 102, and a projection portion 4 that protrudes outward from one axial end of the main body portion 3. That is, the first member 1 comprises four main body portions 3a, 3b, 3c, and 3d and projection portions 4a, 4b, 4c, and 4d. The axial direction of the first member 1 refers to the direction along the axial direction in which the main body portion 3 extends. The circumferential direction of the first member 1 refers to the direction along the arc of the arc-shaped divided body 2.
[0028] The outer circumferential surfaces of the main body portions 3a to 3d of each divided body 2a to 2d are provided with projections 5 that fit into the circulation grooves 122a to 122d formed on the inner circumferential surface of the nut 102. That is, the first member 1 has four projections 5a, 5b, 5c, and 5d. These projections 5a to 5d are provided in accordance with the four circulation grooves 122a to 122d provided on the inner circumferential surface of the nut 102 to be inspected (so that their circumferential phase and axial position coincide). In other words, each projection 5a, 5b, 5c, and 5d is arranged so that their circumferential phase differs by 90° and their axial positions differ. As a result, as shown in Figure 4, when the first member 1 is inserted into the nut 102, the projections 5a to 5d are positioned on the inner diameter side of the four corresponding circulation grooves 122a to 122d.
[0029] As shown in Figure 4, the inner diameter surfaces at both axial ends of the first member 1 are tapered surfaces 6 that widen from the axial inner side to the outer side. The inclination angle of the tapered surface 6 is preferably the same as or approximately the inclination angle of the side wall 14 of the second member 10, which will be described later. Note that the axial inner side and axial outer side of the first member 1 refer to the inner and outer sides with respect to the axial center of the first member 1 (not shown). That is, the axial inner side of the first member 1 is the side closer to the axial center of the first member 1, and the axial outer side of the first member 1 is the side further away from the axial center of the first member 1.
[0030] As shown in Figures 2 and 4, the second member 10 is a frustoconical member 11 whose top surface 12 is a small circle in plan view, its bottom surface 13 is a large circle in plan view, and its side walls 14 are tapered surfaces. In this embodiment, the second member 10 is composed of two frustoconical members 11a and 11b. As shown by arrow D in Figure 4, when the second member 10 is fitted axially inward from both axial ends of the first member 1, as shown in Figure 6, the respective divided parts 2a to 2d of the first member 1 can be moved toward the outer diameter, and the respective projections 5a to 5d fit into the corresponding circulation grooves 122a to 122d.
[0031] As shown in Figures 2 and 4, the positioning member 20 consists of a shaft portion 21 that can be inserted into the nut 102 and a flange portion 22 provided at the axial end of the shaft portion 21. As shown in Figure 4, the shaft portion 21 is a hollow cylindrical body on the inner diameter side, and the flange portion 22 is a disc body with a hole on the inner diameter side. As shown in Figure 4, the outer diameter dimension of the shaft portion 21 is approximately the same as the inner diameter dimension of the nut 102. The inner diameter dimension of the shaft portion 21 is larger than the outer diameter dimension of the main body portions 3a to 3d of the divided bodies 2a to 2d when the divided bodies 2a to 2d of the first member 1 are each positioned towards the center (inner diameter side). This allows the main body portions 3a to 3d of the divided bodies 2a to 2d to be inserted into the positioning member 20. When the main body portions 3a to 3d of the divided bodies 2a to 2d are inserted into the positioning member 20, a sufficient gap is formed between the outer circumferential surfaces of the main body portions 3a to 3d of the divided bodies 2a to 2d and the inner circumferential surface of the shaft portion 21 of the positioning member 20. As a result, the divided bodies 2a to 2d can move radially within the positioning member 20. The axial direction of the positioning member 20 refers to the direction along the axial direction in which the shaft portion 21 extends. The radial direction of the first member 1 refers to the direction perpendicular to the axial direction of the first member 1.
[0032] As shown in Figure 2, the shaft portion 21 has four holes 23a, 23b, 23c, and 23d that penetrate radially. The four holes 23a to 23d are formed with a circumferential phase difference of 90° each and with different axial positions, and are provided at positions corresponding to the arrangement of the circulation grooves 122a to 122d of the nut 102 to be inspected. As a result, as shown in Figure 4, even when the positioning member 20 is inserted inside the nut 102, the circulation grooves 122a to 122d are not blocked by the shaft portion 21 of the positioning member 20, and furthermore, when the first member 1 is inserted inside the positioning member 20, the protrusions 5a to 5d face the circulation grooves 122a to 122d. Note that the radial direction of the positioning member 20 refers to the direction perpendicular to the axial direction of the positioning member 20. Furthermore, the circumferential direction of the positioning member 20 refers to the direction along the arc of the arc-shaped shaft portion 21 and flange portion 22.
[0033] As shown in Figure 2, an arc-shaped recess 24 is provided on one axial end face of the flange portion 22. The circumferential width of the arc-shaped recess 24 is such that the engaging portion 109 of the nut 102 can be fitted into it. When the engaging portion 109 of the nut 102 is fitted into the arc-shaped recess 24, the phases of the circulation grooves 122a to 122d of the nut 102 and the holes 23a to 23d formed in the shaft portion 21 of the positioning member 20 can be aligned.
[0034] Furthermore, a fitting recess 25 extending in the radial direction is provided on the other axial end face of the flange portion 22. In this embodiment, four fitting recesses 25a, 25b, 25c, and 25d are provided at equal pitches of 90° in the circumferential direction. The circumferential width of the fitting recesses 25a to 25d is such that the protrusions 4a to 4d of the divided bodies 2a2 to d of the first member 1 can be fitted into them. When the protrusions 4a to 4d are fitted into the fitting recesses 25a to 25d, the phases of the projections 5a to 5d of the first member 1 and the circulation grooves 122a to 122d are aligned, and the positioning member 20 restricts the axial movement and circumferential rotation of the first member 1, while allowing the radial movement of the first member 1.
[0035] A method for inspecting the depth of the circulation groove formed on the inner surface of a ball screw nut using an inspection device for ball screw nuts having the above configuration will be described. For the inspection, a specified depth d (see Figure 8A) is set for the circulation grooves 122a to 122d of the nut 102 to be inspected. The "specified depth" is an arbitrarily specified depth of the circulation groove for the nut to be inspected, and is predetermined for each inspection.
[0036] One example of a method for defining the specified depth d is to set it as the lower limit and / or upper limit of the allowable range of the depth of the circulation groove 122. The "allowable range of the depth of the circulation groove" is a range H of groove depth (from the lower limit L1 to the upper limit L2) that is considered preferable for the circulation groove 122, as shown in Figures 7A to 7C, and is set in advance. For example, it is considered from the viewpoint of a groove depth that does not hinder the smooth rolling of the balls, and can be set in various ways depending on the ball diameter, the shape of the circulation groove, etc., and is set for each nut to be inspected. As shown in Figure 7A, if the depth of the circulation groove 122 is within the allowable range, the balls will roll smoothly, and the depth of the circulation groove 122 can be said to be preferable. On the other hand, as shown in Figure 7B, if the depth of the circulation groove 122 is less than the lower limit L1 of the allowable range H (shallower than the lower limit L1), or as shown in Figure 7C, if the depth of the circulation groove 122 exceeds the upper limit L2 of the allowable range H (deeper than the upper limit L2), the smooth rolling of the balls is hindered, and the depth of the circulation groove 122 is undesirable.
[0037] As a first method for inspecting the depth of the circulation groove 122, we will describe the case where the specified depth d is set as the lower limit L1 of the allowable range H of the depth of the circulation groove 122. First, the shaft portion 21 of the positioning member 20 is inserted into the nut 102. In this case, when the engaging portion 109 of the nut 102 is fitted into the arc-shaped recess 24, one axial end face (right side in Figure 4) of the flange portion 22 of the positioning member 20 comes into contact with the end of the nut 102. As a result, the phases of the circulation grooves 122a to 122d of the nut 102 and the holes 23a to 23d formed in the shaft portion 21 of the positioning member 20 coincide, and the circulation grooves 122a to 122d are exposed without being blocked by the shaft portion 21 of the positioning member 20.
[0038] Furthermore, the main body portions 3a to 3d of the divided parts 2a to 2d of the first member 1 are inserted into the positioning member 20. In this case, when the protruding portions 4a to 4d of the divided parts 2a to 2d are fitted into the fitting recesses 25a to 25d, the other axial end face of the flange portion 22 (left side in Figure 4) comes into contact with the protruding portions 4a to 4d of the divided parts 2a to 2d. As a result, the phases of the projections 5a to 5d of the first member 1 and the circulation grooves 122a to 122d are aligned, and the positioning member 20 restricts the axial movement and circumferential rotation of the first member 1 while allowing the radial movement of the first member 1. In addition, the positioning member 20 causes the axial position of the first member 1 and the axial position of the inner circumferential surface of the nut 102 to coincide in approximately the same place. In this state, as shown in Figure 4, a gap is formed between the outer circumferential surfaces of the main body portions 3a to 3d of the divided bodies 2a to 2d and the inner circumferential surface of the positioning member 20, allowing the divided bodies 2a and 2d to move radially inside the positioning member 20.
[0039] Next, as shown by arrow D in Figure 4, the second member 10 (frustoconical members 11a, 11b) is fitted into the first member 1 from both axial ends inwards in the axial direction. As a result, as shown in Figures 5 and 6, each of the segments 2a to 2d of the first member 1 moves outwards, and each of the projections 5a to 5d fits into the circulation grooves 122a to 122d. When fitting the second member 10, it is preferable that the center position of the upper surface 12 of the frustoconical member 11 is as close as possible to the axis of the first member 1, and that the fitting direction of the frustoconical member 11 is aligned with the axis of the first member 1. As a result, the four segments 2a to 2d move outwards while maintaining a concentric state with the inner circumferential surface of the nut 102.
[0040] When the projection 5 contacts the bottom of the circulation groove 122, the axial movement of the second member 10 is restricted. Therefore, relative depth information with respect to the specified depth d (in this case, d = L1) of the circulation groove 122 can be obtained from the axial position of the second member 10 when the insertion of the second member 10 is restricted. Specifically, when the second member 10 is inserted, as shown in Figure 8A, if the projection 5 of the first member 1 contacts the specified depth d (i.e., the movement of the second member 10 is restricted), the axial position of the second member 10 becomes a boundary position P that indicates that the circulation groove 122 is at the same depth as the specified depth d (lower limit L1). Here, "relative depth information" refers to depth information compared to the specified depth d, with respect to the specified depth d as the reference. Specifically, it is information that exceeds the specified depth d (is deeper than the specified depth d), is the same as the specified depth d, or is less than the specified depth d (is shallower than the specified depth d).
[0041] As shown in Figure 8A, if the second member 10 can be fitted up to the boundary position P (the fitting of the second member 10 is restricted at the boundary position P), the projection 5 will come into contact with the circulation groove 122 at a specified depth d. Therefore, it can be seen that the groove depth of the circulation groove 122 is the specified depth d. Also, as shown in Figure 8B, if the second member 10 can be fitted axially inward from the boundary position P (the fitting of the second member 10 is restricted axially inward from the boundary position P), the projection 5 will come into contact with the circulation groove 122 at a position deeper than the specified depth d. Therefore, it can be seen that the groove depth of the circulation groove 122 is greater than or equal to the specified depth d. Note that the dashed line in Figure 8B indicates the axial position of the circulation groove 122 at the specified depth d and the second member 10 in that case, and indicates the boundary position P of the circulation groove 122 and the second member 10 in Figure 8A.
[0042] On the other hand, as shown in Figure 8C, if the second member 10 cannot be fitted up to the boundary position P (the fitting of the second member 10 is restricted axially outward from the boundary position P), the projection 5 will come into contact with the circulation groove 122 at a position shallower than the specified depth d. Therefore, it can be seen that the groove depth of the circulation groove 122 is less than the specified depth d. Note that the dashed line in Figure 8C indicates the axial position of the circulation groove 122 at the specified depth d and the second member 10 in that case, and indicates the boundary position P of the circulation groove 122 and the second member 10 in Figure 8A.
[0043] As described above, if the specified depth d is set to the lower limit L1 of the allowable range H, information can be obtained as to whether the depth of the circulation groove 122 exceeds the lower limit L1 (the inspection result is as shown in FIG. 8B), is equal to the lower limit L1 (the inspection result is as shown in FIG. 8A), or is less than the lower limit L1 (the inspection result is as shown in FIG. 8C), and it can be inspected whether the depth of the circulation groove 122 is too shallow. In this case, in FIG. 8A, the depth of the circulation groove 122 is equal to the lower limit L1 of the allowable range H, and in FIG. 8B, the depth of the circulation groove 122 exceeds the lower limit L1 of the allowable range H (is deeper than the lower limit L1), so the inspection is passed. On the other hand, in FIG. 8C, the depth of the circulation groove 122 is less than the lower limit L1 of the allowable range H, and the depth of the circulation groove 122 is too shallow, so the inspection is failed.
[0044] As a second method for inspecting the depth of the circulation groove 122, a case where the specified depth d is set to the upper limit L2 of the allowable range H of the depth of the circulation groove 122 will be described. Also in this case, as shown in FIG. 8A, when the projection 5 of the first member 1 abuts at the specified depth d (that is, the movement of the second member 10 is restricted), the axial position of the second member 10 is the boundary position P indicating that the circulation groove 122 has the same depth as the specified depth d (=L2).
[0045] In the second method, similarly to the first method described above, the second member 10 is fitted axially inward from both axial ends of the first member 1, and relative depth information with respect to the specified depth d (upper limit L2) of the circulation groove 122 is obtained based on the axial position of the second member 10 when the movement of the second member 10 is restricted. That is, information can be obtained as to whether the depth of the circulation groove 122 exceeds the upper limit L2 (the inspection result is as shown in FIG. 8B), is equal to the upper limit L2 (the inspection result is as shown in FIG. 8A), or is less than the upper limit L2 (the inspection result is as shown in FIG. 8C), and it can be inspected whether the depth of the circulation groove 122 is too deep. In this case, in FIG. 8A, the depth of the circulation groove 122 is equal to the upper limit L2 of the allowable range H, and in FIG. 8C, the depth of the circulation groove 122 is less than the upper limit L2 of the allowable range H (is shallower than the upper limit L2), so the inspection is passed. On the other hand, in FIG. 8B, the depth of the circulation groove 122 exceeds the upper limit L2 of the allowable range H, and the depth of the circulation groove 122 is too deep, so the inspection is failed.
[0046] By performing inspections using both the first method (where the specified depth d is the lower limit L1 of the allowable range H) and the second method (where the specified depth d is the upper limit L2 of the allowable range H) on a single nut 102, it is possible to obtain information on whether the depth of the circulation groove 122 is within the allowable range. That is, if the inspection is passed using both the first and second methods, it can be determined that the depth of the circulation groove 122 is within the allowable range of upper limit L1 and lower limit L2, and that the depth of the circulation groove 122 is within a desirable range. On the other hand, if the inspection is not passed using either the first or second method, it can be determined that the depth of the circulation groove 122 is outside the allowable range, and that the depth of the circulation groove 122 is not within a desirable range. In this way, by performing inspections using both the first and second methods, a highly accurate inspection can be performed.
[0047] When detecting the axial position of the second member 10, the position of the entire second member 10 may be detected, or the position of a part of the second member 10 may be detected. For example, the position of the base surface 13 of the frustoconical member 11 may be detected and compared with the position of the base surface at the boundary position P, or only the position of the top surface 12 of the frustoconical member 11 may be detected, or only a specific position of the side wall 14 may be detected. Furthermore, the position of the second member 10 can be detected by various methods, such as visual detection by a human, detection by image processing, or detection by a position sensor. In addition, the comparison between the detected position and the boundary position (pass / fail judgment of the inspection) may be performed by a human or a computer, and if a computer is used, the comparison may be performed by a dedicated program or AI.
[0048] As described above, the ball screw nut inspection apparatus and the ball screw nut inspection method of the present embodiment include the first member 1 and the second member 10, whereby the nut 102 can be inspected non-destructively to determine whether the depth of the circulation groove 122 is equal to or greater than a specified depth d. Further, in the present embodiment, by providing the positioning member 20, the first member is positioned by the positioning member 20, and the protrusion 5 is easily fitted accurately into the circulation groove 122, so that improvement in inspection accuracy and speeding up of inspection can be achieved. Furthermore, since the second member 10 has a tapered surface, the second member 10 can be smoothly fitted into the first member, facilitating inspection.
[0049] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways. The nut to be inspected is not limited to that of the embodiments, and various numbers and forms of circulation grooves can be employed. In that case, the first member and the positioning member having protrusions corresponding to the number and arrangement of the circulation grooves formed on the inner peripheral surface of the nut are used. That is, the number of divided bodies constituting the first member and the number of protrusions are not limited. In the embodiment, the second member is constituted by two truncated cone members, but may be constituted by one truncated cone member. In this case, the second member may be inserted from only one end of the first member, or after inserting the second member from one end of the first member, the second member may be inserted from the other end. In the embodiment, the second member has a truncated cone shape, but it is not limited to a truncated cone shape as long as the side wall has a tapered surface, and may be a truncated pyramid shape, or may be a conical shape or a pyramid shape having no upper surface (having an apex). In the embodiment, the positioning member is used, but the positioning member can be omitted, and the inspection of the present invention can be performed using only the first member and the second member.
[0050] The method for defining the specified depth is not limited to that of the embodiment; any method of defining the specified depth is acceptable. For example, if the depth of the circulation groove of an existing nut is defined as the specified depth, it is possible to inspect whether the depth of the circulation groove of the nut under inspection differs from that of an existing nut. Alternatively, a specific dimensional value may be specified as the groove depth, and this may be defined as the specified depth. In this way, the specified depth can be any depth as long as it is a specified depth.
[0051] This is an inspection device for checking the depth of the circulation groove in ball screw nuts. It can inspect the depth of the circulation groove non-destructively.
[0052] 1 First member 2 Divided body 4 Protruding part 5 Projection 10 Second member 20 Positioning member 22 Flange 25 Fitting recess 102 Nut 121 Rolling groove 122 Circulation groove d Specified depth H Allowable range L1 Lower limit L2 Upper limit
Claims
1. An inspection device for a ball screw nut, wherein a helical groove and a circulation groove for returning the ball from the end to the start of the helical groove are formed on the inner circumferential surface of the ball screw nut, and the device acquires relative depth information with respect to a specified depth of the circulation groove to inspect the depth of the circulation groove, comprising: a first member having a plurality of divided bodies inserted inside the nut and arranged in the circumferential direction, each divided body having a projection on its outer circumferential surface that fits into the circulation groove; and a second member being inserted axially inward from the axial end of the first member, such that each divided body of the first member moves toward the outer diameter side and the projection fits into the circulation groove.
2. The inspection device for ball screw nuts according to claim 1, characterized in that the specified depth is the lower limit of the allowable range of the depth of the circulation groove or the upper limit of the allowable range of the depth of the circulation groove.
3. An inspection device for a ball screw nut according to claim 1, characterized in that it is provided with a positioning member that is inserted inside the nut and restricts the axial movement and circumferential rotation of the first member while allowing the radial movement of the first member, with the projection of the first member and the circulation groove in phase.
4. The ball screw nut inspection device according to claim 3, characterized in that a flange is provided at the axial end of the positioning member, one axial end face of the flange contacts the nut, and the other axial end face of the flange contacts the first member.
5. The inspection device for ball screw nuts according to claim 4, characterized in that each segment of the first member is provided with a radially projecting projection, and the other axial end face of the flange is provided with a fitting recess into which the projection fits.
6. The inspection device for a ball screw nut according to claim 1, characterized in that the inner diameter surface of the axial end of the first member is tapered, expanding in diameter from the axial inner side to the outer side, and the second member has a tapered surface.
7. A method for inspecting the depth of a ball screw nut, comprising: using any of the ball screw nut inspection devices described in claims 1 to 6, inserting the first member into the nut, aligning the phase of the projection of the first member with the phase of the circulation groove, inserting the second member axially inward from the axial end of the first member, moving each divided part of the first member toward the outer diameter side to fit the projection into the circulation groove, and when the insertion of the second member into the first member is restricted, obtaining relative depth information with respect to a specified depth of the circulation groove from the axial position of the second member, thereby inspecting the depth of the circulation groove.