Multi-row ball screw

Abstract

A multi-row ball screw (1) is provided with: a nut (4) having a plurality of helical grooves (40) on an inner peripheral surface; a threaded shaft (3) having a plurality of helical grooves (30) on an outer peripheral surface; and a plurality of balls (6) rollably arranged in a rolling path (20) formed by the plurality of helical grooves (40) of the nut (4) and the plurality of helical grooves (30) of the threaded shaft (3). The helical grooves (40) of the nut (4) have: a first helical groove (41) having left and right flanks (41c) capable of contacting two rows of balls (6) respectively and separated in the axial direction, and two rows of second helical grooves (42) continuous with each row of the first helical groove (41) and having left and right flanks capable of contacting the balls (6) at two points. Thus, a multi-row ball screw with a nut having a U-shaped helical groove accommodating two rows of balls is obtained, which has high dimensional accuracy.

Description

Technical Field

[0001] This invention relates to multi-row ball screws, and more specifically, to multi-row ball screws used in electric injection molding machines, stamping machines, etc., as mechanical elements that convert rotary motion into linear motion. Background Technology

[0002] A ball screw typically comprises a threaded shaft with helical grooves on its outer circumference, a cylindrical nut with helical grooves on its inner circumference and mounted on the outer circumference of the threaded shaft, and multiple balls assembled between the helical grooves. It converts the rotational motion of either the threaded shaft or the nut into the linear motion of the other. For example, Patent Document 1 discloses a low-friction, high-rigidity ball screw with a structure in which the helical grooves of the threaded shaft and the nut are wide and U-shaped (cross-sectional shape), and two rows of balls are arranged in these helical grooves.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 56-147954 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] However, advanced measurement techniques are required to accurately machine the U-shaped helical groove of the nut as described in Patent Document 1. In the case of a Gothic-shaped ball groove, which is a typical ball groove, it is possible to fix a ball with the same diameter as the ball used to the measuring terminal to measure the slant diameter and machine it to the target size. However, in the case of a U-shaped helical groove, since there is no tooth on one side, it is difficult to stably fix the ball of the measuring terminal to the helical groove, making accurate dimensional measurement difficult.

[0008] The present invention was made in view of the above-mentioned problems, and its object is to provide a multi-row ball screw with a nut, wherein the U-shaped helical groove of the nut accommodates two rows of balls and has high dimensional accuracy.

[0009] Technical means for solving problems

[0010] The above-mentioned objective of the present invention is achieved by the following structure.

[0011] A multi-row ball screw, having:

[0012] The nut has multiple rows of helical grooves on its inner circumferential surface;

[0013] A threaded shaft having multiple rows of helical grooves on its outer circumferential surface; and

[0014] Multiple balls are arranged in a rolling path formed by multiple rows of helical grooves of the nut and multiple rows of helical grooves of the threaded shaft in a rollable manner.

[0015] The nut has multiple rows of helical grooves: a U-shaped first helical groove having axially separated left and right teeth that can contact two rows of balls respectively; and two rows of second helical grooves that are continuous with each row of the first helical groove and have left and right teeth that can contact the balls at two points.

[0016] Invention Effects

[0017] According to the multi-row ball screw of the present invention, the accurate slant diameter dimension can be determined by the second helical groove. As a result, the first helical groove can be ground based on the accurate slant diameter dimension, and a multi-row ball screw with a nut and the U-shaped first helical groove of the nut has high dimensional accuracy can be provided. Attached Figure Description

[0018] Figure 1 This is a perspective view of the multi-row ball screw according to one embodiment of the present invention.

[0019] Figure 2 yes Figure 1 A cross-sectional view of a multi-row ball screw.

[0020] Figure 3 This is a cross-sectional view showing the main part of the helical groove of the nut.

[0021] Figure 4 yes Figure 3 An enlarged cross-sectional view of the first spiral groove shown.

[0022] Figure 5 yes Figure 3 An enlarged cross-sectional view of the second spiral groove shown.

[0023] Figure 6 This is a schematic cross-sectional view showing the state of the nut's grinding process.

[0024] Figure 7 This is a general front view showing the state of the nut's grinding process.

[0025] Explanation of reference numerals in the attached figures

[0026] 1. Multi-row ball screw

[0027] 2 threaded shaft

[0028] 4 nuts

[0029] 20 Rolling Road

[0030] 30, 40 spiral grooves

[0031] 41 First spiral groove

[0032] 42 Second spiral groove

[0033] CL central axis

[0034] D-diameter dimension Detailed Implementation

[0035] The following describes in detail, based on the accompanying drawings, the multi-row ball screws involved in the embodiments of the present invention.

[0036] like Figure 1 and Figure 2 As shown, the multi-row ball screw 1 of this embodiment includes: a nut 4 with multiple rows of helical grooves 40 on its inner circumference; a threaded shaft 3 with multiple rows of helical grooves 30 on its outer circumference; and multiple steel balls 6 arranged in a rolling path 20 formed by two helical grooves 40 and 30 in a rolling manner.

[0037] Additionally, sealing rings 10 are embedded, for example, on the inner circumference of both ends of the nut 4 to prevent lubricating oil leakage between it and the threaded shaft 3. The nut 4 is made of a strong and tough steel, such as chromium-molybdenum steel.

[0038] Nut 4 is located at one end of the cylindrical nut body 4a. Figure 1 The left side (in the middle) has a circular flange 8, on which bolt through holes 8a are provided as needed. Therefore, in the multi-row ball screw 1, for example, the threaded shaft 3 is connected to a drive unit (such as the shaft of an electric motor, not shown) and driven to rotate in both directions. On the other hand, the nut 4 is used to fasten a driven component (such as an electric injection molding machine, stamping machine, or handling machine, not shown) to the flange 8 via the bolt through holes 8a.

[0039] On the outer circumferential surface of the nut body 4a, in multiple locations along the circumferential direction ( Figure 1 (Only at point 1 in the figure) A flat surface 9, which appears rectangular when viewed from above, is formed. A pair of return tubes 5 are fastened to each flat surface 9 by tube clamps 7. The return tube 5 is formed by bending a steel pipe into a roughly "U" shape. The two ends of the tube are connected to the rolling path 20 by four through holes formed on the flat surface 9 (through holes connected to the first spiral groove 41). Thus, two rows of ball circulation paths (two loops) are formed through each return tube 5, allowing multiple balls 6 to move and circulate within the rolling path 20.

[0040] Also refer to Figures 3-5The nut 4 has a helical groove 40 comprising: a U-shaped first helical groove 41 having axially separated left and right toothed surfaces 41c capable of contacting the two rows of balls 6 respectively; and two rows of second helical grooves 42, which are continuous with the rows of the first helical grooves 41 and have left and right toothed surfaces 42c capable of contacting the balls 6 at two points. Furthermore, "left and right" refers to... Figure 2 On both sides along the direction of the central axis CL.

[0041] That is, the first spiral groove 41 has a cylindrical groove bottom 41b between adjacent protrusions 43 and between the left and right tooth vents 41c, forming a wide U-shape in the left-right direction. Therefore, in the first spiral groove 41, the left tooth vent 41c and the right tooth vent 41c respectively support two rows of balls 6 in two rings.

[0042] On the other hand, the second spiral groove 42 has left and right teeth 42c with a shape that is approximately equal to the left and right teeth 41c of the first spiral groove, and the left and right teeth 42c are formed into a Gothic arc shape that can contact the ball 6 at two points.

[0043] Furthermore, in this embodiment, the second spiral groove 42 is continuous with the first spiral groove 41 at a position axially outward of the ball lifting portion of the ball circulation path. Therefore, the actual ball 6 does not circulate on the left and right tooth vents 42c, but as described later, a fixture with a sphere the same as the ball 6, or a measuring terminal having a sphere-shaped portion of the same size as the ball 6, is in contact with the left and right tooth vents 42c at two points.

[0044] Additionally, the first spiral groove 41 is an intermediate protrusion 44 formed between the second spiral grooves 42. Figure 5 The first spiral groove 41 is formed by removing the shaded portion (in the middle) of the shape. The first spiral groove 41 is formed by removing the intermediate protrusion 44 after or simultaneously with the formation of the second spiral groove 42.

[0045] The helical groove 30 of the threaded shaft 3 is also configured as a wide U-shaped groove capable of accommodating two balls 6 in the direction of the central axis CL, and has a cross-sectional shape approximately the same as the first helical groove 41 of the nut 4. Therefore, the balls 6 within the helical groove 30 are supported by the toothed flanks 30c formed on the left and right sides. As a material for the threaded shaft 3, strong and tough steel such as chromium-molybdenum steel can be used, for example.

[0046] The spiral groove 30 of the threaded shaft 3 and the first spiral groove 41 of the nut 4 are connected by a protrusion 31 of the threaded shaft 3 facing the axial middle portion of the first spiral groove 41, and a protrusion 43 of the nut 4 facing the axial middle portion of the spiral groove 30, thus forming a rolling path 20. The balls 6 are thus held between the toothed surface 30c of the threaded shaft 3 and the toothed surface 41c of the nut 4. Therefore, the multiple balls 6 assembled between the spiral groove 30 and the first spiral groove 41 roll within the rolling path 20 by rotating the threaded shaft 3 relative to the nut 4, and by rotating the threaded shaft 3, the multiple balls 6 roll within the rolling path 20, allowing the nut 4 to move smoothly axially.

[0047] Furthermore, the two rolling paths 20 form multiple rows (four rows in this embodiment), thereby constituting the multi-row ball screw 1 of this embodiment having multiple rows (at least two rows, i.e., an even number of rows) of rolling paths 20.

[0048] Here, when forming the spiral groove 40 in the nut 4, the first spiral groove 41 and the second spiral groove 42 are machined on the inner circumferential surface of the nut body 4a using a lathe. Afterward, heat treatment (quenching) is performed using a carburizing heat treatment device and a high-frequency heat treatment device.

[0049] Then, machining is performed to form the first helical groove 41 to the specified dimensions. This machining is carried out by turning, but grinding can also be performed after turning. At this time, dimensional measurements are taken to determine the machining amount, and the cutting amount and grinding amount are calculated based on the dimensional measurement results, followed by turning and grinding.

[0050] In dimensional measurement, measuring terminals are used, such as... Figure 3 As shown, the slant diameter D of the second helical groove 42 is measured (the groove dimension when the groove advance is 0.5 lead and the grooves are 180° phase-opposite). Therefore, at least one 0.5 lead remains in the second helical groove 42. Figure 2 (The above is represented by the dimension L).

[0051] Furthermore, the inclined diameter D of the second spiral groove 42 is the same as the inclined diameter of the first spiral groove 41. That is, the first spiral groove 41 is formed by cutting off the middle protrusion 44 between the two rows of second spiral grooves 42, so the inclined diameter D between the grooves of the second spiral groove 42 represents the inclined diameter of the first spiral groove 41.

[0052] Furthermore, during measurement, the ball-shaped fixture or measuring terminal is stably held by the left and right sides of the toothed belly 42c of the second spiral groove 42, thus enabling accurate measurement of the slant diameter dimension D.

[0053] Furthermore, the two rows of spiral grooves are arranged at a 180° phase, so at the same axial position, another row of second spiral grooves 42 is formed on the opposite side of one row of second spiral grooves 42 at a 180° angle. Therefore, as long as there is a short groove that can accommodate the measuring fixture and measuring terminals, the groove length L1 of the second spiral groove 42 only needs to be greater than or equal to the diameter of the ball.

[0054] The results of the above dimensional measurements determine the grinding amount required for the finishing dimension, such as... Figure 6 and Figure 7 As shown, the machining is performed. The boring bar 50 used for grinding has a pair of grinding stones 51 with the shape matching the tooth belly 41c of the first helical groove 41. They are inclined relative to the central axis CL at a lead angle θ along the first helical groove 41. By rotating these grinding stones 51 at high speed, the tooth belly 41c of the adjacent first helical groove 41, which is on the left and right sides relative to the protrusion 43, and the left and right tooth belly 42c of the adjacent second helical groove 42 are machined.

[0055] In this way, by measuring the slant diameter D of the second spiral groove 42 while machining, a nut 4 with a first spiral groove 41 having high dimensional accuracy can be formed.

[0056] Furthermore, the present invention is not limited to the embodiments described above, and can be modified and improved as appropriate.

[0057] For example, in the embodiments described above, a second helical groove 42 for measuring the slant diameter can also be formed on the threaded shaft 3. Thus, by machining the slant diameter of the threaded shaft 3 with high precision, a threaded shaft 3 having a helical groove 30 with high dimensional accuracy can be formed.

[0058] As stated above, the following information is disclosed in this specification.

[0059] (1) A multi-row ball screw, characterized in that it has:

[0060] The nut has multiple rows of helical grooves on its inner circumferential surface;

[0061] A threaded shaft having multiple rows of helical grooves on its outer circumferential surface; and

[0062] Multiple balls are rotatably arranged in a rolling path formed by multiple rows of helical grooves of the nut and multiple rows of helical grooves of the threaded shaft.

[0063] The nut has multiple rows of helical grooves: a U-shaped first helical groove having axially separated left and right teeth that can contact two rows of balls respectively; and two rows of second helical grooves that are continuous with each row of the first helical groove and have left and right teeth that can contact the balls at two points.

[0064] According to this structure, the slant diameter can be accurately measured through the second helical groove. As a result, the first helical groove can be machined based on the accurate slant diameter, and a multi-row ball screw with a nut and the U-shaped helical groove of the nut can be provided with high dimensional accuracy.

[0065] (2) According to the multi-row ball screw described in (1), wherein,

[0066] The second spiral groove has a lead of 0.5 or more.

[0067] Based on this structure, the slant diameter of the second spiral groove can be accurately measured.

[0068] (3) The multi-row ball screw according to (1) or (2), wherein,

[0069] The length of the second spiral groove is greater than or equal to the diameter of the ball.

[0070] Based on this structure, a measuring terminal can be set up to measure the slant diameter in the second spiral groove.

[0071] Furthermore, this application is based on Japanese Patent Application No. 2021-062357, filed on March 31, 2021, the contents of which are incorporated herein by reference.

Claims

1. A multi-row ball screw, characterized in that, have: The nut has multiple rows of helical grooves on its inner circumferential surface; A threaded shaft having multiple rows of helical grooves on its outer circumference; as well as Multiple balls are arranged in a rolling path formed by multiple rows of helical grooves of the nut and multiple rows of helical grooves of the threaded shaft in a rollable manner. The nut has a multi-row spiral groove with a U-shaped first spiral groove, which has axially separated left and right teeth that can contact the two rows of balls respectively. And two rows of second spiral grooves, which are continuous with each row of the first spiral groove, and have left and right toothed flanks that can contact the two points of the ball.

2. The multi-row ball screw according to claim 1, characterized in that, The second spiral groove has a lead of 0.5 or more.

3. The multi-row ball screw according to claim 1 or 2, characterized in that, The length of the second spiral groove is greater than or equal to the diameter of the ball.

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