Ball screw device

Abstract

To provide a ball screw device that is simple and inexpensive to construct, while mitigating the effects of ball screw runout. [Solution] The ball screw device comprises a ball screw having a screw shaft, a nut, and balls that roll within a circulating circuit formed between the screw shaft and the nut; a nut housing connected to a movable body; and a cylindrical elastic body connected to the nut at one end and to the nut housing at the other end of the nut. The cylindrical elastic body is elastically deformed so that the other end of the nut is displaceable relative to the one end of the nut in the radial direction of the nut.

Description

Technical Field

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[0001] The present invention relates to a ball screw device using a ball screw.

Background Art

[0002] For example, there is a ball screw type drive device for reciprocally driving a movable body such as a movable table of a grinding machine. Such a ball screw type drive device includes a nut attached to the movable body and a screw shaft screwed into the nut, and the reciprocating rotation of the screw shaft enables the movable body to be reciprocally driven along the screw shaft via the nut.

[0003] In a ball screw type drive device, due to the machining accuracy of the screw shaft, nut, and balls, etc., there is a risk of the screw shaft vibrating in the radial direction. This affects the motion accuracy such as the straightness (pitching / yawing) of the movable table, and thus has been one of the problems in applying a ball screw to a high-precision movable table.

[0004] In contrast, Patent Document 1 discloses a ball screw type drive device having a connecting means for connecting a nut member and a movable body via a plurality of balls in the axial direction, the connecting means having a rolling element arrangement groove for arranging the plurality of balls in the circumferential direction of the screw shaft, and the rolling element arrangement groove being formed in a non-circular shape when viewed from the axial direction or in a circular shape whose center does not coincide with the axis of the screw shaft when viewed from the axial direction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to the ball screw drive device described in Patent Document 1, the nut member and the movable body are rigidly connected in the axial direction, while the runout during rotation of the screw shaft in the radial direction can be absorbed by the contact fluctuation of the balls in the rolling element arrangement groove. In other words, the connecting means of Patent Document 1 can improve positional accuracy by constraining the movable body in the axial direction, while keeping the movable body in a floating state in the radial direction, so as not to transmit the runout during rotation of the screw shaft to the movable body.

[0007] However, the ball screw type drive device described in Patent Document 1 has problems such as high manufacturing costs due to the large number of parts and the requirement that the rolling element arrangement grooves be elliptical.

[0008] This invention has been made in view of the above problems, and aims to provide a ball screw device that can mitigate the effects of the runout of the ball screw while having a simple and inexpensive configuration. [Means for solving the problem]

[0009] The ball screw device of the present invention is A ball screw having a screw shaft, a nut, and a ball that rolls within a circulating circuit formed between the screw shaft and the nut, A nut housing connected to the movable body, The nut has a cylindrical elastic body connected to the nut at one end and connected to the nut housing at the other end of the nut, As the cylindrical elastic body undergoes elastic deformation, the other end of the nut becomes displaceable relative to one end of the nut in the radial direction. It is characterized by the following: [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a ball screw device that can mitigate the effects of the ball screw's runout while having a simple and inexpensive configuration. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a plan view of a linear motion table using a ball screw device according to the first embodiment. [Figure 2] Figure 2 is an enlarged axial cross-sectional view of a ball screw device according to the first embodiment. [Figure 3] Figure 3 is a plan view of a cylindrical elastic body. [Figure 4] Figure 4 is an enlarged axial cross-sectional view of a ball screw device according to the second embodiment. [Modes for carrying out the invention]

[0012] (First embodiment) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Figure 1 is a plan view of a linear motion table 1 using the ball screw device 10 according to this embodiment, but a part of the ball screw device 10 is shown in an axial cross-section. Figure 2 is an enlarged axial cross-sectional view of the ball screw device 10.

[0013] The linear motion table 1 comprises a base 2 fixed to a rigid body, a motor 3 mounted on the base 2 and equipped with a rotating shaft 3a, a screw shaft 4, a coupling device 5 that connects the end of the rotating shaft 3a and the end of the screw shaft 4 in a power-transmitting manner, and bearings 6 and 7 that rotatably support both ends of the screw shaft 4 relative to the base 2. The male helical groove formed on the outer circumference of the screw shaft 4 is shown in a simplified diagram.

[0014] The ball screw device 10 includes a ball screw 11, a cylindrical elastic body 12, and a cylindrical nut housing 13.

[0015] The ball screw 11 comprises a screw shaft 4, a cylindrical nut 14 positioned around the screw shaft 4 and having a female helical groove on its inner circumference, and a ball (not shown) positioned between the male helical groove of the screw shaft 4 and the female helical groove of the nut 14. The nut 14 has a first flange portion 14a that protrudes radially outward from one end in the axial direction (the right end in Figure 2).

[0016] Both ends of the rolling path consisting of the male spiral groove and the female spiral groove are connected to a circulation path (not shown), thereby forming a closed circulation circuit, and the ball can roll along the circulation circuit.

[0017] FIG. 3 is a plan view of the cylindrical elastic body 12. The cylindrical elastic body 12 is made of, for example, resin, and has a cylindrical portion 12a and a second flange portion 12b that protrudes radially outward from one end in the axial direction (the left end in FIG. 3). The cylindrical portion 12a is disposed on the outer periphery of the nut 14, and at this time, the second flange portion 12b is disposed on the end side opposite to the nut 14 with respect to the first flange portion 14a.

[0018] The cylindrical portion 12a has a plurality (here, two) of spiral slits 12c penetrating the inner and outer circumferences. The number of slits 12c may be one or three or more. The plurality of slits 12c are non-communicating with each other, and it is preferable that one slit 12c extends in a range exceeding 360° around the axis, for example, 400° or more and 460° or less.

[0019] In FIG. 2, a first bolt 15 inserted into an axially penetrating hole (not shown) formed in the first flange portion 14a of the nut 14 is screwed into a threaded hole (not shown) formed at the axial end of the cylindrical portion 12a of the cylindrical elastic body 12 facing the first flange portion 14a, whereby one end of the cylindrical elastic body 12 is connected to the nut 14 via the first flange portion 14a.

[0020] Further, a second bolt 16 inserted into an axially penetrating hole (not shown) formed in the second flange portion 12b of the cylindrical elastic body 12 is screwed into a threaded hole (not shown) formed at the axial end of the nut housing 13 facing the second flange portion 12b, whereby the other end of the cylindrical elastic body 12 is connected to the nut housing 13. That is, the nut 14 and the nut housing 13 are connected via the cylindrical elastic body 12. A table (not shown) as a movable body is connected to the nut housing 13.

[0021] Within the cylindrical space between the outer circumference of the nut 14 and the inner circumference of the nut housing 13, the cylindrical portion 12a of the cylindrical elastic body 12 is arranged with a slight gap in the radial direction.

[0022] As the screw shaft 4 rotates relative to the nut 14, multiple balls circulate within the circulation circuit, making it possible to cause the nut 14 to move linearly relative to the screw shaft 4 in the axial direction of the screw shaft 4.

[0023] Here, due to the machining accuracy of the screw shaft 4, nut 14, and ball, there is a risk that runout of the screw shaft 4 may occur in the radial direction. In such a case, if the nut 14 is displaced radially relative to the base 2 due to the runout of the screw shaft 4, one end of the cylindrical elastic body 12 will also be displaced in the same direction. However, according to this embodiment, since the nut 14 and one end of the cylindrical elastic body 12 are connected, and the nut housing 13 and the other end of the cylindrical elastic body 12 are connected, the displacement of the nut housing 13 that is accompanied by the displacement of the nut 14 can be suppressed by the elastic deformation of the cylindrical elastic body 12. Therefore, regardless of the displacement of the nut 14, the positioning accuracy of the nut housing 13 in the direction perpendicular to the axis of the screw shaft 4 can be ensured.

[0024] On the other hand, since the cylindrical elastic body 12 has higher axial rigidity than radial rigidity, no axial relative displacement of the nut housing 13 occurs with respect to the nut 14, and the positioning accuracy of the nut housing 13 in the axial direction of the screw shaft 4 can be ensured. Note that "axial rigidity is higher than radial rigidity" means that the force F1 required to displace the nut housing 13 a predetermined distance in the axial direction relative to the nut 14 is greater than the force F2 required to displace the nut housing 13 a predetermined distance in the radial direction relative to the nut 14.

[0025] In addition, the cylindrical elastic body 12 is positioned radially outside the nut 14 and radially inside the nut housing 13, and its length is almost equal to the lengths of the nut 14 and the nut housing 13. Therefore, even with the cylindrical elastic body 12 installed, the axial range of motion of the ball screw 11 remains almost unchanged. Furthermore, since the ball screw device 10 has a simple configuration consisting only of attaching the cylindrical elastic body 12 to the ball screw 11, manufacturing costs can be kept low.

[0026] (Second embodiment) Figure 4 is an enlarged axial cross-sectional view of the ball screw device 10A according to the second embodiment. In this embodiment, only the cylindrical elastic body 12A differs from the first embodiment; the other components (including the ball screw 11) are the same as in the first embodiment, so a redundant explanation is omitted.

[0027] The cylindrical elastic body 12A has a first cylindrical portion 12Aa with a second flange portion 12Ab, a second cylindrical portion 12Ad, a plurality of coil springs 12Ae, and a plurality of leaf springs 12Af. The first cylindrical portion 12Aa and the second cylindrical portion 12Ad are arranged in series around the nut 14.

[0028] A first bolt 15, inserted through an axial through hole (not shown) formed in the first flange portion 14a of the nut 14, is screwed into a threaded hole (not shown) formed at the axial end of the second cylindrical portion 12Ad of the cylindrical elastic body 12A facing the first flange portion 14a, thereby connecting the outer end of the second cylindrical portion 12Ad to the nut 14 via the first flange portion 14a.

[0029] Furthermore, a second bolt 16, inserted through an axial through hole (not shown) formed in the second flange portion 12Ab of the cylindrical elastic body 12A, is screwed into a threaded hole (not shown) formed at the axial end of the nut housing 13 facing the second flange portion 12Ab, thereby connecting the outer end of the first cylindrical portion 12Aa to the nut housing 13.

[0030] Multiple blind holes 12Ag are formed at the inner end of the first cylindrical portion 12Aa, and multiple blind holes 12Ah are formed at the inner end of the second cylindrical portion 12Ad opposite to it. Coil springs 12Ae are inserted into the blind holes 12Ag and 12Ah, biasing the first cylindrical portion 12Aa and the second cylindrical portion 12Ad apart. Both ends of a leaf spring 12Af are attached to the outer circumference of the first cylindrical portion 12Aa and the outer circumference of the second cylindrical portion 12Ad using rivets (not shown), and the leaf spring 12Af connects the first cylindrical portion 12Aa and the second cylindrical portion 12Ad in the axial direction. Preferably, the coil springs 12Ae and the leaf springs 12Af are arranged at equal intervals in the circumferential direction. The coil springs 12Ae may be omitted. The springs are not limited to those described above.

[0031] In this embodiment as well, within the cylindrical space between the outer circumference of the nut 14 and the inner circumference of the nut housing 13, the cylindrical portion of the first cylindrical portion 12Aa other than the second flange portion 12Ab, and the second cylindrical portion 12Ad are arranged with a slight gap in the radial direction.

[0032] According to this embodiment, if the nut 14 is displaced radially relative to the base 2 due to the runout of the screw shaft 4, the second cylindrical portion 12Ad will also be displaced in the same direction. However, since the second cylindrical portion 12Ad and the first cylindrical portion 12Aa are connected by an elastically deformable coil spring 12Ae and a leaf spring 12Af, even if the second cylindrical portion 12Ad is displaced radially, the displacement of the first cylindrical portion 12Aa and the nut housing 13 in the same direction can be suppressed. Therefore, regardless of the displacement of the nut 14, the positioning accuracy of the nut housing 13 in the direction perpendicular to the axis of the screw shaft 4 can be ensured.

[0033] On the other hand, since the leaf spring 12Af has higher rigidity in the longitudinal direction compared to its rigidity in the bending direction, no axial relative displacement occurs between the second cylindrical portion 12Ad and the first cylindrical portion 12Aa. Therefore, no axial relative displacement occurs between the nut housing 13 and the nut 14, and the positioning accuracy of the nut housing 13 in the axial direction of the screw shaft 4 can be ensured.

[0034] The present invention is not limited to the embodiments described above. Within the scope of the present invention, any component of the embodiments described above can be modified. Furthermore, any component can be added to or omitted in the embodiments described above. For example, the present invention can be applied to ball screw devices having various ball screws, such as circulating ball screws, tube-type ball screws, deflector-type ball screws, and end-cap-type ball screws. [Explanation of symbols]

[0035] 1 Linear motion table 2 bases 3 motors 4 Screw shaft 6,7 Bearings 10,10A Ball Screw Device 11 Ball screw 12,12A Cylindrical elastic body 12Aa First cylindrical section 12Ad Second cylindrical section 12Ae coil spring 12Af leaf spring 13 Nut Housing 14 nuts 15. First bolt 16. Second bolt

Claims

1. A ball screw having a screw shaft, a nut, and a ball that rolls within a circulating circuit formed between the screw shaft and the nut, A nut housing connected to the movable body, The nut has a cylindrical elastic body connected to the nut at one end and connected to the nut housing at the other end of the nut, As the cylindrical elastic body undergoes elastic deformation, the other end of the nut becomes displaceable relative to one end of the nut in the radial direction. A ball screw device characterized by the following features.

2. The cylindrical elastic body is placed in the cylindrical space formed between the outer circumference of the nut and the inner circumference of the nut housing. The ball screw device according to feature 1.

3. The tubular elastic body has a cylindrical portion with a spiral slit, The ball screw device according to claim 1 or 2.

4. The cylindrical elastic body has a first cylindrical portion connected to the nut housing, a second cylindrical portion connected to the nut, and a spring connecting the first cylindrical portion and the second cylindrical portion. As the spring elastically deforms, the first cylindrical portion becomes displaceable relative to the second cylindrical portion in the radial direction of the nut. The ball screw device according to claim 1 or 2.

5. The cylindrical elastic body has axial stiffness that is higher than radial stiffness. The ball screw device according to claim 1 or 2.

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