Ball screw

Abstract

To provide a ball screw which can replace a circulation component while preventing the erroneous insertion of balls into a circuit external rolling path by a simple structure.SOLUTION: A plurality of circuits C1, C2 are formed of portions of a ball circulation passage 41 of circulation components 40A, 40B and a ball rolling path 25 between both end parts 42, 43 of the circulation components 40A, 40B. The ball rolling path 25 is partitioned into a plurality of circuit internal rolling paths 25a in which balls 26 can roll, and a circuit external rolling path 25b which is arranged outside the plurality of circuits C1, C2, and in which the balls 26 do not exist. An intrusion prohibition part 45 protruding into the circuit external rolling path 25b at a tip 45a, and prohibiting the intrusion of the balls 26 into the circuit external rolling path 25b is arranged in the vicinity 25c of an inlet of the circuit external rolling path 25b at a connecting part of the circuit internal rolling paths 25a and the circuit external rolling path 25b.SELECTED DRAWING: Figure 2A

Description

Technical Field

[0001] The present invention relates to a ball screw, and more particularly to a ball screw that prevents a ball from being erroneously inserted into a ball rolling path outside the circuit.

Background Art

[0002] A ball screw is used as a mechanical element in, for example, semiconductor manufacturing equipment, compression molding machines, injection molding machines, general transfer devices, etc. This ball screw has a path through which the balls circulate. As the structure of the circulation path, a structure in which a ball circulation tube or a ball circulation piece is disposed in the body portion of the nut, and ball circulation passages are disposed at both front and rear ends of the nut is known. The circulation path (circuit) using a ball circulation tube or a ball circulation piece is provided in one or more series for each nut. When there are a plurality of series of circuits, there is a groove portion (rolling path outside the circuit) where the balls do not circulate, that is, the balls do not pass, between one circuit and another adjacent circuit.

[0003] Normally, there is no ball in the rolling path outside the circuit between the plurality of circuits. However, if the ball screw is operated in a state where a ball is erroneously inserted during the ball filling operation or the like, the ball cannot circulate, so there is a risk of serious damage such as locking of the ball screw.

[0004] Normally, the ball screw is in an assembled state when delivered to the customer and is assembled without being disassembled when assembled to the mechanical device. However, when used for a long time, the ball screw often needs to be completely replaced. In the case of ball circulation parts, etc., it may be possible to recover by replacing the parts. Also, in the case of part replacement, it is rare to remove the ball screw from the mechanical device, and it is common to perform part replacement with the ball screw mounted on the mechanical device.

[0005] While factory manufacturing processes employ assembly techniques to prevent balls from entering the external rotation pathways of the circuit, the same methods used in factory manufacturing cannot typically be applied when replacing circulating components or other parts while they are installed in machinery, potentially leading to the accidental insertion of balls into the external rotation pathways.

[0006] Patent documents 1 and 2 disclose a ball screw that prevents balls from entering the non-circulating part of the nut's screw groove by making the angled diameter of the screw groove portion that constitutes the non-circulating part of the ball (outside the circuit) smaller than the angled diameter of the screw groove portion that constitutes the circuit (inside the circuit). Patent document 3 also describes a ball screw equipped with a sensor capable of detecting a ball when it enters the outside of the circuit. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 7-253146 [Patent Document 2] Japanese Patent Publication No. 2015-218755 [Patent Document 3] Japanese Patent Publication No. 2017-150502 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the ball screws described in Patent Documents 1 and 2 have the problem of increased manufacturing costs due to the complex machining method of the screw grooves in the nuts. Furthermore, the ball screw described in Patent Document 3 is capable of detecting balls that have mistakenly entered the circuit's external rotation path, but it cannot prevent the balls from being mistakenly inserted into the circuit's external rotation path.

[0009] This invention has been made in view of the aforementioned problems, and its purpose is to provide a ball screw that allows for the replacement of circulating parts while preventing the ball from being mistakenly inserted into the external rotation path of the circuit with a simple structure. [Means for solving the problem]

[0010] The above objective of the present invention is achieved by the following configuration. [1] A ball screw comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove formed on its inner circumference opposite to the screw groove of the screw shaft; a plurality of balls arranged to be rotatable in a ball rolling path between the screw groove of the screw shaft and the screw groove on the inner circumference; and a plurality of circulating components forming a ball circulation passage for circulating the balls rolling in the ball rolling path, Multiple ball circulation circuits are formed by the respective ball circulation passages of each of the aforementioned circulation components and the respective portions of the ball rolling paths partitioned by the respective ball circulation passages. The ball rolling path is divided into a plurality of internal circuit rolling paths, each separated by the respective ball circulation passages, on which the balls can roll, and an external circuit rolling path provided outside the plurality of circuits where the balls do not exist. A ball screw comprising an entry-blocking portion positioned near the entrance of the outer circuit rolling path at the connection point between the inner circuit rolling path and the outer circuit rolling path, which protrudes into the outer circuit rolling path to prevent the ball from entering the outer circuit rolling path. [Effects of the Invention]

[0011] The ball screw of the present invention has a simple structure that prevents the ball from being mistakenly inserted into the external rotation path of the circuit, thereby improving maintainability such as parts replacement, and preventing serious damage such as ball screw lock. [Brief explanation of the drawing]

[0012] [Figure 1] This is a longitudinal cross-sectional view of a ball screw according to one embodiment of the present invention. [Figure 2A] This is a schematic cross-sectional view of one of the circuits near the line II-II in Figure 1. [Figure 2B] Figure 1 shows a schematic cross-sectional view of one of the circuits near the II'-II' line. [Figure 3] This cross-sectional view shows how the entry prevention section prevents the ball from being mistakenly inserted into the ball rolling path outside the circuit. [Modes for carrying out the invention]

[0013] Hereinafter, one embodiment of the ball screw according to the present invention will be described in detail with reference to the drawings. As shown in Figure 1, the ball screw 10 of this embodiment is a mechanism that converts rotational motion into linear motion, comprising a screw shaft 20 having a helical screw groove 21 formed on its outer circumference, a nut 30 having a helical screw groove 31 formed on its inner circumference opposite to the screw groove 21 of the screw shaft 20, and a number of balls 26 arranged to roll in a ball rolling path 25 formed by the screw groove 21 of the screw shaft 20 and the screw groove 31 of the nut 30.

[0014] Two roughly U-shaped circulation tubes 40A and 40B are attached to the nut 30, which are ball circulation members for returning the balls 26 that have rolled in the ball rolling path 25 to their predetermined positions in the ball rolling path 25. The U-shaped circulation tubes 40A and 40B are provided with a ball circulation passage 41 inside which the balls 26 rolling in the ball rolling path 25 are circulated, and the two U-shaped circulation tubes 40A and 40B, along with the respective parts of the ball rolling path 25 partitioned by the two U-shaped circulation tubes 40A and 40B (circuit internal rolling path 25a), form two circuits C1 and C2 that allow the balls 26 to circulate indefinitely.

[0015] Thus, when the ball screw 10 includes a plurality of circuits C1 and C2, the ball rolling path 25 is partitioned by the U-shaped circulation tubes 40A and 40B into a plurality of in-circuit rolling paths 25a where the balls 26 roll, and an out-of-circuit rolling path 25b that is formed between the plurality of circuits C1 and C2 and outside the plurality of circuits C1 and C2 and where no ball 26 exists.

[0016] Also, as shown in FIGS. 2A and 2B, the nut 30 is provided with a total of four ball circulation holes 33, two each, that communicate from both ends of the in-circuit rolling paths 25a of the respective circuits C1 and C2 along the normal direction of the in-circuit rolling paths 25a at both ends to the outer peripheral surface 32. Further, the nut 30 is formed with an internal thread 34 that penetrates in the radial direction from the outer peripheral surface 32 near the entrance 25c of the out-of-circuit rolling path 25b at the connection portion between the in-circuit rolling path 25a and the out-of-circuit rolling path 25b of each of the circuits C1 and C2.

[0017] The ball circulation holes 33 are holes for sequentially inserting and loading the balls 26 into the in-circuit rolling paths 25a, and are also holes for connecting the ball circulation passage 41 and the in-circuit rolling paths 25a by inserting both end portions 42 and 43 of the U-shaped circulation tubes 40A and 40B therethrough.

[0018] Also, a bolt 45, which is an entry prevention portion, is screwed into the internal thread 34. The tip 45a of the bolt 45 protrudes into the out-of-circuit rolling path 25b in a state where it does not contact the thread groove 21 of the screw shaft 20. Thereby, when inserting the ball 26 from the ball circulation hole 33 into the in-circuit rolling path 25a, it is possible to prevent the ball 26 from being erroneously inserted into the out-of-circuit rolling path 25b. Further, since the bolt 45 does not interfere with the out-of-circuit rolling path 25b (thread groove 21), there is no risk of hindering the operation of the ball screw 10.

[0019] Note that FIGS. 2A and 2B respectively show the vicinity of the connection between the in-circuit rolling path 25a and the out-of-circuit rolling path 25b at both ends of the U-shaped circulation tube 40B of one circuit C2. The configuration of the vicinity of the connection between the in-circuit rolling path 25a and the out-of-circuit rolling path 25b at both ends of the U-shaped circulation tube 40A of the other circuit C1 is the same.

[0020] When replacing the U-shaped circulation tubes 40A and 40B of the ball screw 10 with such a structure, as shown in FIG. 3, first, remove the U-shaped circulation tubes 40A and 40B scheduled for replacement from the nut 30 together with the balls 26 loaded in the U-shaped circulation tubes 40A and 40B.

[0021] Then, insert the balls 26 as needed into the ball circulation holes 33 of the nut 30 in a state where the screw shaft 20 is inserted and the U-shaped circulation tubes 40A and 40B are removed, and fill the in-circuit rolling path 25a with the balls 26.

[0022] When a predetermined number of balls 26 are filled in the in-circuit rolling path 25a, insert both ends 42 and 43 of the new U-shaped circulation tubes 40A and 40B, which are separately filled with the balls 26 in advance, into the ball circulation holes 33 of the nut 30, and fix the U-shaped circulation tubes 40A and 40B with a fixture (not shown) to complete the replacement of the U-shaped circulation tubes 40A and 40B.

[0023] When replacing the U-shaped circulation tubes 40A and 40B as described above, with conventional ball screws 10, the balls 26 may enter the circuit external rotation path 25b when removing and installing the U-shaped circulation tubes 40A and 40B from the nut 30. If the ball screw 10 is operated with the balls 26 mistakenly inserted into the circuit external rotation path 25b where the balls 26 should not be present, the balls 26 may interfere with the U-shaped circulation tubes 40A and 40B, preventing the balls 26 from circulating and potentially causing the ball screw 10 to lock up. Even if the ball screw 10 does not lock up, the balls 26 will continue to slip between the screw shaft 20 and the nut 30, accelerating wear on the balls 26, screw shaft 20, and nut 30, which may lead to abnormalities such as abnormal noise and vibration at an early stage.

[0024] On the other hand, in this embodiment, the ball screw 10 has a bolt 45a that protrudes near the entrance 25c of the circuit's external rotation passage 25b. Therefore, when removing the U-shaped circulation tubes 40A and 40B from the nut 30, and when installing them, the bolt 45 prevents the ball 26 from entering the circuit's external rotation passage 25b, and the ball 26 is not accidentally inserted into the circuit's external rotation passage 25b.

[0025] In particular, as shown in Figure 3, even when the U-shaped circulation tubes 40A and 40B are replaced with the ball circulation hole 33 facing horizontally, making it easy for the ball 26 to enter the circuit's external rotation path 25b, the ball 26 will not be accidentally inserted into the circuit's external rotation path 25b. Furthermore, the ball 26 may remain near the entrance 25c of the circuit's external rolling path 25b, but in that case, the ball 26 can be easily removed using tweezers or a magnet.

[0026] Therefore, in the ball screw 10 of this embodiment, the maintainability of parts such as the U-shaped circulation tube 40 is improved, and serious damage such as the ball screw 10 locking up can be prevented.

[0027] (modified version) In the modified ball screw 10, the tip 45a of the bolt 45, which is the entry-blocking part, is magnetized with a magnetic force capable of attracting metal wear particles. Wear particles generated by the operation of the ball screw 10 tend to cause initial wear at the position where the balls 26 move between the load-bearing area and the non-load-bearing area within the circuits C1 and C2, that is, near the connection point (settling area 27) between the internal circuit rolling path 25a and the U-shaped circulation tubes 40A and 40B.

[0028] As the ball screw 10 operates, wear particles are dispersed into the nut 30 (ball rolling path 25) via the lubricant, causing them to get stuck between the ball 26 and the screw grooves 21 and 31, resulting in indentations and surface roughness, which is undesirable as it negatively affects the lifespan of the ball screw 10.

[0029] However, in this embodiment, the ball screw 10 has a bolt 45 with magnetic properties at its tip 45a positioned near the pole of the bearing 27 where initial wear is likely to occur. This allows for the immediate capture of generated wear debris, effectively preventing its diffusion into the ball rolling path 25. Furthermore, the wear debris captured by the magnetic force of the bolt 45 is held in place by the magnetic force, preventing it from re-diffusing into the ball rolling path 25.

[0030] Furthermore, the bolt 45 is designed to be easily removed from the outside of the nut 30, and if wear debris accumulates on the tip 45a of the bolt 45 due to magnetic attraction, the bolt 45 alone can be removed from the nut 30 to easily remove the wear debris.

[0031] In the modified example, if the ball 26 that remains near the entrance 25c of the circuit's external rolling path 25b is removed by a magnet, the magnetic force of the magnet must be stronger than the magnetic force of the bolt 45.

[0032] Furthermore, the present invention is not limited to the embodiments and examples described above, and can be modified, improved, etc., as appropriate. For example, although the entry prevention mechanism was described as a bolt in the above explanation, it is not particularly limited to any mechanism that can prevent the ball from entering the outer rotation path of the circuit, and pins or the like can also be used. Furthermore, although the ball screw was described as a tube-type ball screw using a U-shaped circulating tube as a circulating component, it may also be a spool-type ball screw using circulating spools.

[0033] As described above, the following matters are disclosed in this specification: (1) A ball screw comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove formed on its inner circumference opposite to the screw groove of the screw shaft; a plurality of balls arranged to roll in a ball rolling path between the screw groove of the screw shaft and the screw groove on the inner circumference; and a plurality of circulating components forming a ball circulation passage for circulating the balls rolling in the ball rolling path, Multiple ball circulation circuits are formed by the respective ball circulation passages of each of the aforementioned circulation components and the respective portions of the ball rolling paths partitioned by the respective ball circulation passages. The ball rolling path is divided into a plurality of internal circuit rolling paths, each separated by the respective ball circulation passages, on which the balls can roll, and an external circuit rolling path provided outside the plurality of circuits where the balls do not exist. A ball screw comprising an entry-blocking portion positioned near the entrance of the outer circuit rolling path at the connection point between the inner circuit rolling path and the outer circuit rolling path, which protrudes into the outer circuit rolling path to prevent the ball from entering the outer circuit rolling path. This configuration allows for the replacement of circulating parts while preventing the ball from being mistakenly inserted into the external rotation path of the circuit through a simple structure.

[0034] (2) The ball screw according to (1), wherein the entry blocking portion is a bolt or pin fixed to the nut and whose tip protrudes into the circuit's outer rolling path. This configuration allows for a simple structure that prevents the ball from being mistakenly inserted into the external rotation path of the circuit.

[0035] (3) The ball screw according to (1) or (2), wherein the tip of the entry-blocking portion that protrudes into the outside rolling path of the circuit is equipped with a magnetic force capable of attracting metal wear particles. With this configuration, wear particles generated during the operation of the ball screw can be attracted and removed by magnetic force, allowing the ball screw to be kept in good condition for a long period of time. [Explanation of symbols]

[0036] 10 Ball screws 20 Screw shaft 21 Screw groove 25 Ball Rolling Path 25a Circuit Inner Rotation Path 25b Circuit Outward Movement 25c Near the entrance 26 balls 30 nuts 31 Screw groove 40A, 40B U-shaped circulation tube (circulation component) 41 Ball circulation passage 42, 43 Both ends 45 bolts (intrusion prevention part) 45a Tip C1, C2 Circuit

Claims

1. A ball screw comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove formed on its inner circumference opposite to the screw groove of the screw shaft; a plurality of balls arranged to roll in a ball rolling path between the screw groove of the screw shaft and the screw groove on the inner circumference; and a plurality of circulating components forming a ball circulation passage for circulating the balls rolling in the ball rolling path, Multiple ball circulation circuits are formed by the respective ball circulation passages of each of the aforementioned circulation components and the respective portions of the ball rolling paths partitioned by the respective ball circulation passages. The ball rolling path is divided into a plurality of internal circuit rolling paths, each separated by the respective ball circulation passages, on which the balls can roll, and an external circuit rolling path provided outside the plurality of circuits where the balls are not present. The circuit includes an entry blocking portion located near the entrance of the circuit outer rolling path at the connection point between the circuit inner rolling path and the circuit outer rolling path, which protrudes into the circuit outer rolling path to prevent the ball from entering the circuit outer rolling path. The tip of the entry-blocking portion that protrudes into the external rolling path of the circuit is a ball screw equipped with a magnetic force capable of attracting metal wear particles.

2. The ball screw according to claim 1, wherein the entry blocking portion is a bolt or pin fixed to the nut, with its tip protruding into the circuit's outer rolling path.

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