Inspection apparatus, inspection method, and manufacturing method for ball screw nuts

Abstract

Ball screw nuts having rolling grooves and circulation grooves are suitably inspected. [Solution] The inspection device 8 for the ball screw nut 3 comprises an inspection ball screw shaft 9 having inspection rolling grooves 17 formed on its outer circumference, a plurality of inspection balls 10 arranged between the inspection rolling grooves 17 of the inspection ball screw shaft 9 and the rolling grooves 3a of the ball screw nut 3, a drive device 12 that rotates the inspection ball screw shaft 9 and the ball screw nut 3 relative to each other, and a torque detection device 13 that detects the torque of the drive device 12.

Description

Technical Field

[0001] The present invention relates to an inspection apparatus, an inspection method, and a manufacturing method for a ball screw nut used in a ball screw device. Background Art

[0002] In a ball screw device, a large number of balls are rollably disposed in a ball rolling path formed by a rolling groove formed on the inner peripheral surface of the ball screw nut and a rolling groove formed on the outer periphery of the ball screw shaft. 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] The ball circulation path that returns balls from the end point to the start point of the ball rolling path is generally formed on a member separate from the nut body (for example, a deflector member). In this case, fixing the deflector member to the nut completes the nut having the ball rolling path and the ball circulation path.

[0004] On the other hand, in recent years, ball screw devices have been proposed in which a circulation groove functioning as a ball circulation path is directly formed on the inner peripheral surface of the ball screw nut, thereby achieving cost reduction compared to a case where the circulation groove is formed on a member separate from the ball screw nut (see, for example, Patent Document 1).

[0005] Patent Document 1 discloses a method for manufacturing a ball screw nut used in such a ball screw device. This method includes a circulation groove forming step and a rolling groove forming step (see paragraphs 0041 to 0051 of the same document).

[0006] In the circulation groove forming step, the circulation groove is formed on the inner peripheral surface of a cylindrical blank by plastic working (see paragraph 0041 of the same document). In the rolling groove forming step, after the circulation groove forming step, a rolling groove connected to the circulation groove formed on the inner peripheral surface of the blank is formed by cutting (see paragraph 0049 of the same document).

[0007] Subsequently, the ball screw nut undergoes various processes such as finishing and heat treatment (see paragraphs 0052 and 0053 of the same document). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6015444 [Overview of the project] [Problems that the invention aims to solve]

[0009] In ball screw nuts manufactured as described above, the circulation groove is deeper than the rolling groove, resulting in a step at the connection point between the two. If this connection point is not formed with sufficient precision, the smooth movement of balls from the circulation groove to the rolling groove may be hindered. Therefore, it is desirable to inspect the circulation groove and rolling groove formed in the ball screw nut at an early stage of the manufacturing process.

[0010] One possible inspection method involves bringing a measuring probe (contact probe) into contact with the bottom of the circulation groove and the bottom of the rolling groove to check the condition of each groove. However, bringing a measuring probe into contact with the bottom of the circulation groove and rolling groove formed on the inner surface of a cylindrical ball screw nut is difficult and cumbersome.

[0011] While it is possible to inspect the circulation groove and rolling groove by cutting the ball screw nut, this would render the ball screw nut unusable as a product; therefore, non-destructive inspection is preferred.

[0012] The present invention has been made in view of the above circumstances, and its technical objective is to suitably inspect a ball screw nut having rolling grooves and circulation grooves. [Means for solving the problem]

[0013] The present invention is for solving the above problems and is an inspection device for a ball screw nut having a circulation groove and a rolling groove on its inner circumferential surface, characterized in that it comprises an inspection ball screw shaft having an inspection rolling groove formed on its outer circumferential surface, a plurality of inspection balls disposed between the inspection rolling groove of the inspection ball screw shaft and the rolling groove of the ball screw nut, a drive device for relative rotation of the inspection ball screw shaft and the ball screw nut, and a torque detection device for detecting the torque of the drive device.

[0014] With this configuration, multiple inspection balls can be placed between the rolling groove of the ball screw nut to be inspected and the inspection rolling groove of the ball screw shaft to be inspected, and an inspection device that can function as a ball screw device can be assembled. In this inspection device, the inspection balls can move in a circulating manner between the rolling paths formed by the respective rolling grooves and the circulation paths formed by the circulation grooves.

[0015] The torque detection device can detect the torque acting on the drive mechanism while the ball screw shaft for inspection and the ball screw nut to be inspected are rotating relative to each other. By comparing the torque value detected by the torque detection device with a reference value, the quality of the ball screw nut can be determined.

[0016] This makes it possible to inspect the rolling grooves and circulation grooves of the ball screw nut efficiently and promptly without damaging the nut.

[0017] In an inspection device for a ball screw nut having the above configuration, it is preferable that the rolling groove of the ball screw nut is formed by rough machining and is a groove before finish machining is performed.

[0018] In a ball screw nut inspection device having the above configuration, it is preferable that the inspection rolling groove of the inspection ball screw shaft has a smaller diameter than the rolling groove of the ball screw shaft incorporated into the finished ball screw device.

[0019] A ball screw nut having a rolling groove formed by rough machining is turned into a finished product by performing finishing on the rolling groove. This finishing process increases the depth of the rolling groove. That is, the depth of the rolling groove when the ball screw nut is inspected is shallower than the depth of the rolling groove when completed.

[0020] In the present invention, as described above, by making the diameter of the inspection rolling groove of the inspection ball screw shaft smaller than that of the rolling groove of the ball screw shaft related to the finished product, the depth of the inspection rolling groove can be made greater than the depth of the rolling groove of the ball screw shaft related to the finished product.

[0021] This makes it possible to form a ball rolling path that suitably allows the inspection balls to roll through the shallower rolling groove of the ball screw nut and the deeper inspection rolling groove of the inspection ball screw shaft.

[0022] In the ball screw nut inspection device having the above configuration, it is preferable that the outermost diameter of the inspection ball screw shaft is the same as the outermost diameter of the ball screw shaft incorporated in the finished ball screw device.

[0023] According to this configuration, by using an inspection ball screw shaft having the same outermost diameter as that of the finished product, inspection can be performed under the same conditions as when the ball screw nut is incorporated into the finished ball screw device.

[0024] The present invention is intended to solve the above problem, and is a ball screw nut inspection method for inspecting the ball screw nut using the above inspection device, characterized in that when the drive device causes the inspection ball screw shaft and the ball screw nut to rotate relative to each other, the quality of the ball screw nut is determined by detecting the torque of the drive device.

[0025] According to this configuration, the quality of the ball screw nut can be determined by comparing the torque value detected by the torque detection device with a reference value. Thereby, the rolling groove of the ball screw nut can be suitably inspected without destroying the ball screw nut.

[0026] A method for manufacturing a ball screw nut according to the present invention is provided to solve the above problem, and is characterized by comprising: a circulation groove forming step of forming the circulation groove on an inner peripheral surface of a cylindrical blank; a rolling groove forming step as a rough machining step of forming the rolling groove on the inner peripheral surface of the blank; and an inspection step of inspecting the ball screw nut after the rolling groove forming step by the above ball screw nut inspection method.

[0027] According to this configuration, by performing the inspection step after the rolling groove forming step which is a rough machining step, the circulation groove and the rolling groove can be appropriately inspected at an early stage without damaging the ball screw nut. Effects of the Invention

[0028] According to the present invention, a ball screw nut having a rolling groove and a circulation groove can be suitably inspected. Brief Description of the Drawings

[0029] [Figure 1] It is a partial longitudinal sectional view of a ball screw device. [Figure 2] It is a cross-sectional view of a main part of the ball screw nut in FIG. 1. [Figure 3] It is an enlarged longitudinal sectional view of the ball circulation path in FIG. 1. [Figure 4] It is a side view showing an inspection apparatus for a ball screw nut. [Figure 5] It is a flowchart showing a method for manufacturing a ball screw nut. Mode for Carrying Out the Invention

[0030] Hereinafter, modes for carrying out the present invention will be described with reference to the drawings. FIGS. 1 to 3 show an embodiment of a ball screw device as a finished product. FIGS. 4 and 5 show an embodiment of an inspection apparatus and a manufacturing method (inspection method) for a ball screw nut according to the present invention.

[0031] As shown in Figure 1, the finished ball screw device 1 comprises a ball screw shaft 2 with a helical rolling groove 2a formed on its outer circumference, a ball screw nut 3 with a helical rolling groove 3a formed on its inner circumference opposite to the rolling groove 2a of the ball screw shaft 2, a plurality of balls 5 that are rotatably loaded in a helical ball rolling path 4 formed by both rolling grooves 2a and 3a, and a ball circulation path 6 that circulates the balls 5 back from the end point to the starting point of the ball rolling path 4.

[0032] The ball 5 moves within the ball rolling path 4, rotates around the ball screw shaft 2, and reaches the end of the ball rolling path 4. There, it is picked up from one end of the ball circulation path 6, passes through the ball circulation path 6, and is returned to the starting point of the ball rolling path 4 from the other end of the ball circulation path 6.

[0033] The ball screw device 1 is configured such that when the ball screw nut 3, which is screwed onto the ball screw shaft 2 via the balls 5, is rotated relative to the ball screw shaft 2, the ball screw shaft 2 and the ball screw nut 3 move relative to each other in the axial direction via the rolling motion of the balls 5.

[0034] An endless ball passage is formed by the ball rolling path 4 and the ball circulation path 6, and the balls 5 rolling in the ball rolling path 4 circulate infinitely within the endless ball passage. Therefore, the ball screw shaft 2 and the ball screw nut 3 can move relative to each other continuously. The cross-sectional shape of the ball rolling path 4 may be either an arc or a Gothic arch.

[0035] The materials of the ball screw shaft 2, ball screw nut 3, and ball 5 are not particularly limited, and common materials such as metal, steel, and ceramics can be used.

[0036] As shown in Figures 2 and 3, a portion of the cylindrical inner surface of the ball screw nut 3 is concave to form a circulation groove 7, and this concave circulation groove 7 serves as the ball circulation path 6. Therefore, unlike known ball circulation types such as tube type and spindle type, no separate component constituting the ball circulation path is attached to the ball screw nut 3. The cross-sectional shape of the circulation groove 7 may be either an arc or a Gothic arch.

[0037] One end of the circulation groove 7 is connected to the end of the ball rolling path 4, and the other end of the circulation groove 7 is connected to the starting point of the ball rolling path 4.

[0038] As shown in Figures 1 and 2, the depth DP2 of the circulation groove 7 is deeper than the depth DP1 of the rolling groove 3a of the ball screw nut 3. The depth DP2 of the circulation groove 7 is deeper than the depth DP3 of the rolling groove 2a of the ball screw shaft 2.

[0039] As shown in Figure 3, the ball 5 that has rolled to the end of the ball rolling path 4 is scooped up from one end of the ball circulation path 6 and sinks into the inside of the ball screw nut 3, that is, radially outward (towards the bottom of the circulation groove 7). Then, it passes through the ball circulation path 6, over the threads 2b between the rolling grooves 2a of the ball screw shaft 2, and is returned to the starting point of the ball rolling path 4 from the other end of the ball circulation path 6.

[0040] Figure 4 shows an inspection device 8 for a ball screw nut 3. The inspection device 8 comprises an inspection ball screw shaft 9, a plurality of inspection balls 10, a support member 11, a drive device 12, and a torque detection device 13. The ball screw nut 3 to be inspected, which has undergone rough machining and before finishing, is mounted on the inspection device 8.

[0041] The inspection ball screw shaft 9 has a first end 14a, a second end 14b, and a threaded portion 15 formed between the first end 14a and the second end 14b. The first end 14a is cylindrical and rotatably supported by a bearing 16. The second end 14b is cylindrical and connected to the drive unit 12 via a connecting member 20.

[0042] The threaded portion 15 is formed in the middle of the inspection ball screw shaft 9. The threaded portion 15 has an inspection rolling groove 17 on its outer circumferential surface. The inspection rolling groove 17 is configured to have a smaller diameter than the rolling groove 2a of the ball screw shaft 2 (see Figure 1) that will be incorporated into the finished ball screw device 1. That is, the root diameter D2 (see Figure 4) of the inspection rolling groove 17 is smaller than the root diameter D1 (see Figure 1) of the rolling groove 2a of the ball screw shaft 2 in the finished product (D2 <D1)。

[0043] The depth DP4 of the inspection rolling groove 17 in the inspection ball screw shaft 9 (see Figure 4) is deeper than the depth DP3 of the rolling groove 2a in the ball screw shaft 2 of the finished product (DP4 > DP3). The depth DP4 of the inspection rolling groove 17 is deeper than the depth DP1a of the rolling groove 3a of the ball screw nut 3 to be inspected (DP4 > DP1a).

[0044] The outermost diameter DM2 (see Figure 4) of the ball screw shaft 9 used for inspection is the same diameter as the outermost diameter DM1 (see Figure 1) of the ball screw shaft 2 that will be incorporated into the finished ball screw device 1 (DM2 = DM1).

[0045] Multiple inspection balls 10 are arranged in an inspection rolling path 18, which is formed by the inspection rolling groove 17 of the inspection ball screw shaft 9 and the rolling groove 3a of the ball screw nut 3 to be inspected. The diameter of the inspection balls 10 is equal to the diameter of the balls 5 that will be incorporated into the finished ball screw device 1.

[0046] The support member 11 is for supporting the ball screw nut 3 to be inspected in a way that prevents it from rotating. The support member 11 has a clamping structure that grips the outer circumferential surface of the ball screw nut 3, but the structure of the support member 11 is not limited to this embodiment and may be a flange portion integrally formed on the outer circumferential surface of the ball screw nut 3.

[0047] The drive unit 12 is used to rotate the inspection ball screw shaft 9 and the ball screw nut 3 relative to each other. In this embodiment, the drive unit 12 is composed of, for example, an electric motor, but is not limited to this configuration. The rotating shaft 19 of the drive unit 12 is concentrically connected to the second end 14b of the inspection ball screw shaft 9 by a connecting member 20.

[0048] The torque detection device 13 is for detecting the torque acting on the rotating shaft 19 of the drive unit 12. In this embodiment, the torque detection device 13 is a torque meter attached to the rotating shaft 19 of the drive unit 12. The torque meter has a display unit that displays the measured torque value.

[0049] The manufacturing method (inspection method) for the ball screw nut 3 will be described below. As shown in Figure 5, this method comprises a preparation step S1, a circulation groove formation step S2, a rolling groove formation step (rough machining step) S3, an inspection step S4, a heat treatment step S5, and a finishing step S6.

[0050] In preparation step S1, a cylindrical blank material is formed by performing plastic deformation such as cold forging on a cylindrical steel material.

[0051] Next, in the circulation groove formation process S2, circulation grooves 7 are formed on the inner circumferential surface of the blank material. That is, recesses, which serve as circulation grooves 7, are formed on the inner circumferential surface of the blank material by plastic deformation such as cold forging.

[0052] In the subsequent rolling groove formation process S3, rolling grooves 3a are formed on the inner circumferential surface of the blank material as a rough machining process. Specifically, rolling grooves 3a that connect to the circulation grooves 7 are formed on the inner circumferential surface of the blank material by cutting. This forms the ball screw nut 3, which will be the object of inspection in the next inspection process S4.

[0053] The inspection process S4 is for inspecting the ball screw nut 3, which has rolling grooves 3a and circulation grooves 7 formed on its inner circumferential surface, before the heat treatment process S5 and the finishing process S6.

[0054] In inspection step S4, inspection balls 10 are placed between the rolling groove 3a of the ball screw nut 3 to be inspected (the ball screw nut 3 after the rolling groove forming step S3 and before the heat treatment step S5) and the inspection rolling groove 17 of the inspection ball screw shaft 9, thereby assembling an inspection device 8 that can function as a ball screw device.

[0055] Subsequently, the drive unit 12 rotates the inspection ball screw shaft 9 and the ball screw nut 3 relative to each other, and the torque acting on the drive unit 12 is measured to determine whether the ball screw nut 3 is good or bad.

[0056] Specifically, in inspection step S4, while the inspection ball screw shaft 9 is being rotated by the drive unit 12, the torque acting on the rotating shaft 19 of the drive unit 12 is measured by the torque detection device 13. Furthermore, by comparing this measured torque value with a pre-prepared reference value, the quality of the ball screw nut 3 being inspected is determined.

[0057] In other words, if the measured torque value is below the standard value, the ball screw nut 3 is judged to be acceptable (good product), and if the measured torque value exceeds the standard value, the ball screw nut 3 is judged to be unacceptable (defective product).

[0058] In inspection step S4, the reference torque value is preferably set to 1.5 times the torque value detected by the torque detection device 13 when the ball screw device 1 of the finished product (good product) is driven by the drive device 12. For example, if the step at the connection point between the rolling groove 3a and the circulation groove 7 of the ball screw nut 3 to be inspected is not formed with sufficient precision, an excessive torque will act on the ball screw nut 3 when the inspection ball 10 rolls between the rolling groove 3a and the circulation groove 7. In inspection step S4, the defect in the ball screw nut 3 can be detected by detecting this excessive torque with the torque detection device 13.

[0059] In heat treatment step S5, a hardened layer is formed on the surface (outer and inner surfaces) of the ball screw nut 3 by carburizing, quenching, and tempering. The heat treatment in heat treatment step S5 is not limited to this, and various heat treatments such as high-frequency induction hardening and carbonitriding can be used.

[0060] The finishing process S6 is a process of finishing the rolling grooves 3a formed on the inner circumferential surface of the ball screw nut 3. Specifically, a known grinding process is performed on the rolling grooves 3a. The depth DP1 (see Figure 1) of the rolling grooves 3a of the ball screw nut 3 after the finishing process S6 is deeper than the depth DP1a (see Figure 4) of the rolling grooves 3a before the finishing process S6. Note that the grinding process in the finishing process S6 is not performed on the circulation grooves 7 of the ball screw nut 3. Therefore, the depth DP2 of the circulation grooves 7 does not change before and after the finishing process S6.

[0061] According to the ball screw nut 3 inspection device 8 and manufacturing method (inspection method) of this embodiment described above, in inspection step S4, the torque detection device 13 can detect the torque acting on the drive device 12 while the ball screw shaft 9 for inspection and the ball screw nut 3 to be inspected are rotating relative to each other. By comparing the torque value detected by the torque detection device 13 with a reference value, the quality of the ball screw nut 3 can be determined. This makes it possible to suitably inspect the rolling groove 3a and the circulation groove 7 without damaging the ball screw nut 3.

[0062] In inspection step S4, the rolling groove 3a of the ball screw nut 3 being inspected is in the state before the finishing process S6, so its depth DP1a is shallower than the depth DP1 of the rolling groove 3a of the finished product. In this regard, the depth DP4 of the inspection rolling groove 17 on the inspection ball screw shaft 9 of the inspection device 8 is made deeper than the depth DP3 of the rolling groove 2a on the ball screw shaft 2 of the finished product. In this way, the shallow rolling groove 3a in the ball screw nut 3 and the deep inspection rolling groove 17 on the inspection ball screw shaft 9 make it possible to configure an inspection rolling path 18 suitable for the rolling of inspection balls 10 having the same diameter as the balls 5 in the finished ball screw device 1.

[0063] The rolling groove 3a of the ball screw nut 3, formed in the rough machining process (rolling groove formation process S3), is in the state before the finishing process S6. Therefore, when the inspection ball 10 is rolled along this rolling groove 3a, a larger torque is applied to the inspection ball screw shaft 9 compared to when the ball 5 is rolled in the rolling groove 3a of the finished ball screw nut 3. For this reason, it is desirable to set the reference value for inspecting the torque detected by the torque detection device 13 in the inspection process S4 to be greater than the torque applied when the ball screw device 1 of the finished product (good product) is driven by the drive device 12. For example, regarding the reference value of torque in the inspection process S4, it is preferable to use a value of 1.5 times or less as the pass / fail judgment reference value when the pass / fail reference value of the torque of the finished product (good product) is set to 1 times.

[0064] Furthermore, the present invention is not limited to the configuration of the above embodiments, nor is it limited to the effects described above. The present invention can be modified in various ways without departing from the spirit of the invention.

[0065] In the above embodiment, a method for manufacturing a ball screw nut was illustrated in which the heat treatment step S5 is performed after the inspection step S4, but the present invention is not limited thereto. For example, the inspection step S4 may be performed after the heat treatment step S5 and before the finishing step S6. [Explanation of Symbols]

[0066] 1. Finished ball screw device 2 Ball screw shaft 2a Rolling grooves of the ball screw shaft 3. Ball screw nut 3a Rolling grooves of ball screw nut 7 Circulation groove 8. Inspection equipment 9. Ball screw shaft for inspection 10 Inspection Balls 12 Drive unit 13 Torque detection device 17 Rolling groove for inspection S2 Circulation groove formation process S3 Rolling groove forming process (rough machining process) S4 Inspection Process

Claims

1. An inspection device for a ball screw nut having a circulation groove and a rolling groove on its inner circumferential surface, An inspection ball screw shaft having inspection rolling grooves formed on its outer surface, A plurality of inspection balls are arranged between the inspection rolling groove of the inspection ball screw shaft and the rolling groove of the ball screw nut, A drive device for rotating the inspection ball screw shaft and the ball screw nut relative to each other, An inspection device for a ball screw nut, comprising a torque detection device for detecting the torque of the drive device.

2. The ball screw nut inspection device according to claim 1, wherein the rolling groove of the ball screw nut is formed by rough machining and is a groove before finish machining is performed.

3. The ball screw nut inspection device according to claim 2, wherein the inspection rolling groove of the inspection ball screw shaft is smaller in diameter than the rolling groove of the ball screw shaft incorporated into the finished ball screw device.

4. The ball screw nut inspection device according to claim 3, wherein the outermost diameter of the ball screw shaft used for inspection is the same as the outermost diameter of the ball screw shaft incorporated into the finished ball screw device.

5. A method for inspecting a ball screw nut, comprising inspecting the ball screw nut using an inspection device described in any one of claims 1 to 4, A method for inspecting a ball screw nut, wherein the drive device rotates the inspection ball screw shaft and the ball screw nut relative to each other, and the torque of the drive device is detected to determine whether the ball screw nut is good or bad.

6. A circulation groove forming step in which the circulation groove is formed on the inner circumferential surface of a cylindrical blank material, A rolling groove forming step is a rough machining step in which the rolling grooves are formed on the inner circumferential surface of the blank material, A method for manufacturing a ball screw nut, comprising: an inspection step of inspecting the ball screw nut after the rolling groove forming step by the ball screw nut inspection method described in claim 5.

Images