JP4727247B2 - Top ball screw - Google Patents

Description

  The present invention relates to a top-type ball screw used for general industrial machine tools, automobile actuators, and the like, and in particular, aims to improve reliability against dropping of a piece member from a nut.

  In ball screws used for general industrial machine tools, automobile actuators, and the like, there is a strong demand for a compact nut outer diameter, and a top-type ball screw is often used. The piece member used for the top-type ball screw is an important part for circulating the ball between the opposing screw grooves of the ball screw shaft and the nut. Damage to the piece member or dropping from the nut is caused by the function of the actuator. Since it becomes a fatal defect, sufficient countermeasures are required.

  The top-type ball screw piece member fixing structure used in ordinary general industrial machines has a piece member inserted into a piece member fitting opening provided on the nut from the outer side of the nut, and the piece member in the opening. It is common to fill the space on the outer diameter side of the nut with putty. However, such a piece member fixing method may cause the piece member to fall off the nut.

In order to prevent the piece member from falling off, as shown in FIG. 8, as shown in FIG. 8, an arm portion 19 that engages with the screw groove 16 of the nut 12 is provided integrally with the piece member 14, and the piece member 14 is pivoted with respect to the nut 12. Some are positioned in a direction (for example, Patent Document 1). In this case, the piece member 14 is fitted into the piece member fitting opening 21 of the nut 12 from the inner diameter side of the nut, and the nut screw groove 16 is brought into contact with the inner surface of the portion not used for ball circulation. Position with respect to. Further, the piece member 14 is fixed to the nut by crimping the crimping portion 20 formed on the outer diameter side of the piece member 14 to the nut 12.
In the structure having the same structure, the piece member 14 is inserted into the nut 12 from the inner diameter side, and the arm portion 19 prevents the piece member 14 from coming off in the nut outer diameter direction. Is expensive.
JP 2001-132911 A

In the structure for preventing the dropping of the piece member 14 in FIG. 8, the arm portion 19 receives a pulling load applied to the connecting groove 18 of the piece member 14. Examples of the unloading load in this case include a centrifugal force due to the revolution of the ball 13 and a radial component force when the ball 13 rides on the inner surface of the nut screw groove 16 from the connecting groove 18 of the piece member 14.
When such a drop load is received, the arm portion 19 is deformed and a ball circulation failure occurs, or the reliability of the piece member 14 with respect to dropping off from the nut 12 is reduced, but in order to avoid these problems. No particular mention is made in Patent Document 1 regarding measures for improving the strength of the arm portion 19.

  The cause of the deformation of the arm portion 19 in the piece member 14 is that the arm portion 19 is deformed by receiving a bending stress or a shearing stress when the piece member 14 receives a load. In general, the inner diameter of the piece member does not interfere with the outer diameter surface of the ball screw shaft, and the ball that revolves on the rolling path formed between the screw groove facing the ball screw shaft and the nut is the piece member. In order to smoothly introduce into the connecting groove, the BDC (ball center diameter) size is set. In FIG. 8 which shows the case of patent document 1, the said internal diameter dimension of the piece member 14 is shown by A. In FIG. That is, in the case of Patent Document 1, the cross-sectional shape of the arm portion 19 is substantially semicircular. However, if the cross section of the arm portion 19 is semicircular, the rigidity of the arm portion 19 cannot be increased, and thus the above-described deformation of the arm portion 19 cannot be prevented.

Further, in the top ball screw disclosed in Patent Document 1, the ball 12 revolved along the lead angle as shown in FIG. 8 is introduced into the S-shaped connecting groove 18 of the piece member 14. The ball 12 abuts against the wall of the connection groove 18 (the contact position is indicated by a symbol P), so that the ball 12 is guided along the connection groove 18 while gradually changing the ball trajectory, and the outer diameter surface of the ball screw shaft. Is moved between the adjacent nut screw grooves 16, 16.
However, since the cross-sectional shape of the arm portion 19 of the piece member 14 is semicircular as described above, FIGS. 9A and 9B are enlarged views of the c portion and the d portion in FIGS. 8A and 8B. As in B), the contact position P between the ball 13 and the connecting groove 18 becomes the edge portion of the piece member 14.
As a result, the ball 13 is caught at the contact position P due to variations in the inner diameter dimension A of the piece member 14 due to processing accuracy, variations in the caulking fixing position of the piece member 14, and the outer diameter surface of the ball screw shaft is reduced. There is a possibility that the ball 13 cannot get over smoothly, and there is a problem that the vibration and torque characteristics during ball circulation deteriorate. However, the above Patent Document 1 does not mention any improvement measures for such a problem.

  An object of the present invention is to provide a top-type ball screw that can eliminate defective ball circulation, improve the effect of preventing a piece member from falling off a nut, and improve vibration and torque characteristics during ball circulation. It is.

A top type ball screw of the present invention includes a ball screw shaft, a nut, a plurality of balls arranged in a rolling path formed between screw threads facing the ball screw shaft and the nut, and the nut. A plurality of piece members having connecting grooves for connecting the screw grooves, and the piece members are fitted into the piece member fitting openings provided in the nut from the inner diameter side of the nut, in the circumferential direction of the deflector type ball screw having a pair of a over arm portion for positioning which engages with the screw groove of the upper Symbol nut extend in opposite directions, a substantially circular cross-sectional shape of the arm part, the arm portions extend in an arcuate shape along the thread groove of the nut, the outer peripheral surface of the arm portion of this, the radius of curvature of the arc along the groove width center of the screw groove of the nut, the inner surface of the screw groove of the nut Curvature at the center of groove width Larger than the diameter, and the inner surface of the thread groove of the arm portion and the nut are in contact with no load position is the tip of the arm part, the arm part when a load loss in the bridge member is loaded the nut It is characterized by being in contact with the inner surface of the screw groove along the circumferential direction .
As described above, when the cross-sectional shape of the arm portion of the piece member is substantially circular, the rigidity of the arm portion is improved, so that the arm portion is prevented from being deformed by an unloading load applied to the piece member. Therefore, it is possible to eliminate the ball circulation failure due to the deformation of the arm portion, and to improve the reliability with respect to the dropping of the piece member from the nut.
In addition, since the cross-sectional shape of the arm portion is substantially circular, the contact area between the wall of the connecting groove and the ball is expanded at a position where the ball introduced into the connecting groove of the piece member contacts the wall of the connecting groove, The ball is stable and easily gets over the outer diameter surface of the ball screw shaft. As a result, the ball circulates stably, and the vibration and torque characteristics during the ball circulation can be improved together with the improvement in rigidity due to the substantially circular cross section of the arm portion.

In this invention, the piece member may be a sintered body obtained by granulating a kneaded material of metal fine powder and a binder, injection-molding the granulated material, and sintering. The piece member may be manufactured by so-called MIM (Metal Injection Molding).
The piece member having the arm portion has a complicated shape and is difficult to form by cutting or the like, but can be manufactured at low cost by molding with the MIM.

  In the present invention, the piece member may be provided with a pair of projecting piece-shaped crimping portions that are crimped to a mouth edge of the nut member fitting opening on the nut outer diameter side. Thus, by providing a pair of crimping portions on the piece member and crimping the piece member on the lip of the opening for fitting the piece member, the piece member can be easily fixed to the nut only by fitting operation.

A top type ball screw of the present invention includes a ball screw shaft, a nut, a plurality of balls arranged in a rolling path formed between screw threads facing the ball screw shaft and the nut, and the nut. A plurality of piece members having connecting grooves for connecting the screw grooves, and the piece members are fitted into the piece member fitting openings provided in the nut from the inner diameter side of the nut, in the circumferential direction of the deflector type ball screw having a pair of a over arm portion for positioning which engages with the screw groove of the upper Symbol nut extend in opposite directions, a substantially circular cross-sectional shape of the arm part, the arm portions extend in an arcuate shape along the thread groove of the nut, the outer peripheral surface of the arm portion of this, the radius of curvature of the arc along the groove width center of the screw groove of the nut, the inner surface of the screw groove of the nut Curvature at the center of groove width Larger than the diameter, and the inner surface of the thread groove of the arm portion and the nut are in contact with no load position is the tip of the arm part, the arm part when a load loss in the bridge member is loaded the nut Because it is in contact with the inner surface of the screw groove along the circumferential direction , ball circulation failure is eliminated, the effect of preventing the piece member from falling off the nut is improved, and vibration and torque characteristics during ball circulation can be improved. It becomes.

  An embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, this top-type ball screw includes a ball screw shaft 1, a nut 2, and a plurality of balls 3. The nut 2 is configured by attaching a piece member 4 to a nut body 2a. . The ball screw shaft 1 has a thread groove 5 on the outer periphery. The nut 2 has a thread groove 6 facing the thread groove 5 of the ball screw shaft 1 on the inner periphery of a nut body 2a formed in a cylindrical shape. The ball 3 is arranged continuously to a rolling path 7 formed between the screw groove 5 of the ball screw shaft 1 and the screw groove 6 of the nut 2.

  The piece member 4 is a member having a generally oval shape with a connecting groove 8 that connects adjacent ones of the thread grooves 6 of the nut 2, and the connecting groove 8 has an S shape. The thread groove 6 of the nut 2 is connected by the connection groove 8 to form a continuous circulation path of one turn. The depth of the connecting groove 8 is such that the ball 3 can exceed the thread of the screw groove 5 of the ball screw shaft 1 in the connecting groove 8. 2A to 2C show a perspective view, a back view, and a side view of the piece member 4, and FIGS. 5A and 5B show a longitudinal sectional view and a transverse sectional view of the nut 2. The nut body 2a is provided with a piece member fitting opening 11 penetrating the inner and outer peripheral surfaces, and the piece member 4 is fitted into the piece member fitting opening 11 from the inner diameter side.

  The piece member 4 has a pair of arm portions 9 and 9 that engage with the thread groove 6 of the nut 2 to position the piece member 4 in the axial direction with respect to the nut body 2a. These arm portions 9 and 9 are designed to improve rigidity by forming a cross-sectional shape into a substantially circular columnar shape. These arm portions 9, 9 are provided on the inner diameter side of the piece member 4 so as to extend in an arc shape along the thread groove 6 of the nut 2 in directions opposite to each other in the circumferential direction of the nut 2. As shown in FIG. 3, the curvature radius R ′ of the arc along the groove width center of the nut screw groove 6 on the outer peripheral surface of the arm portion 9 is larger than the curvature radius R of the groove width center on the inner surface of the nut screw groove 6. The position where the arm portion 9 and the inner surface of the nut screw groove 6 are in contact with each other without load is the tip of the arm portion 9. The radii of curvature R and R ′ are radii of curvature in the projected shape of the thread groove 6 and the arm portion 9 on a plane perpendicular to the axis of the nut body 2a.

  After the piece member 4 is fitted into the piece member fitting opening 11 from the inner diameter side of the nut on the outer diameter side of the piece member 4, that is, the surface portion facing the outer diameter side of the piece member fitting opening 11 in the nut body 2a. Thus, a pair of protruding piece-like crimping portions 10 and 10 are provided that are fastened to the edge of the piece member fitting opening 11 on the nut outer diameter side.

  The piece member 4 is fitted into the piece member fitting opening 11 in the nut main body 2a from the inner diameter surface side to engage the pair of arm portions 9 and 9 with the nut screw groove 6, and the pair of caulking portions of the piece member 4 10 and 10 are fixed to the nut main body 2a by caulking to the edge of the opening 11 for fitting the piece members. In this way, the pair of caulking portions 10 and 10 of the piece member 4 are fastened to the edge of the piece member fitting opening 11 on the nut outer diameter side, so that the piece member 4 can be simply fitted into the nut. It can be fixed to the main body 2a.

The piece member 4 has a complicated shape and is difficult to form by cutting or the like, but can be manufactured at a low cost by molding with the MIM. The manufacturing process of the piece member 4 by MIM will be described below.
The manufacturing process of MIM is performed by the following procedures: (1) kneading of metal fine powder and binder, (2) granulation, (3) injection molding, (4) debinding, and (5) sintering. In the process after the injection molding, the part not received by the base surface is deformed in the direction of gravity by its own weight until the work is baked and hardened. When the workpiece is the piece member 4, the sintering is performed using the crimping portion 10 side as a base surface. As a result, the arm portion 9 of the piece member 4 is deformed downward by its own weight, and therefore, by adjusting the sintering conditions, a desired desired arm portion shape (that is, the radius of curvature R ′) that is stable without increasing the cost. Can be molded.

  According to the top type ball screw having this configuration, as described above, since the arm portion 9 has a columnar shape with a substantially circular cross section, the rigidity is improved as compared with a conventional semicircular cross section. Therefore, it is possible to prevent the arm portion 9 from being deformed by a pull-out load applied to the piece member 4, eliminate the ball circulation failure due to the deformation of the arm portion 9, and reliability against dropping of the piece member 4 from the nut 2. Can be improved.

  Further, the arm portion 9 of the piece member 4 is formed in a columnar shape having a substantially circular cross section so as to increase the rigidity, so that the ball introduced into the S-shaped connecting groove 8 of the piece member 4 as shown in FIG. The positions P at which 3 abuts against the wall of the connecting groove 8 are as shown in FIGS. 6A and 6B, which are enlarged views of portions a and b in FIGS. 5A and 5B. The contact area between the wall 8 and the ball 3 is enlarged, and the ball 3 can easily get over the outer diameter surface of the ball screw shaft 1 stably. As a result, the ball 3 circulates stably, and vibration and torque characteristics during ball circulation are improved.

  Further, as shown in FIG. 4 (A) by enlarging the B portion of FIG. 3, in this embodiment, the curvature radius R ′ of the arm portion 9 is larger than the curvature radius R of the nut screw groove 6. In the state, the position where the arm portion 9 and the inner surface of the nut screw groove 6 come into contact is the tip of the arm portion 9. When a slipping load is applied to the piece member 4, the arm portion 9 is slightly elastically deformed as shown in FIG. 4B and comes into contact with the inner surface of the nut screw groove 6 along the circumferential direction. Therefore, a sufficient contact area can be secured between the arm portion 9 and the nut screw groove 6, and the rigidity against the pulling force of the piece member 4 can be improved. That is, when the radius of curvature R ′ of the arm portion 9 and the radius of curvature R of the nut screw groove 6 are equal, the arm 9 is elastically deformed like a bow when the pulling force acts on the piece member 4, and the arm portion 9 is Only the base end will be in contact with the nut screw groove 6 and the rigidity against pull-out load may be insufficient. However, as described above, there is a difference in the radius of curvature so that only the tip of the arm 9 is in contact with no load. By doing so, the deformation of the arm portion 9 with respect to the pull-out load is prevented, and poor circulation of the ball due to the deformation of the arm portion 9 is prevented.

  In the above embodiment, the outer peripheral shape of the piece member 4 is oval. However, the shape is not limited to this, and the outer peripheral shape of the piece member 4 may be circular as shown in FIG.

(A) And (B) is the front view and sectional drawing of the top-type ball screw concerning one Embodiment of this invention. (A) is a perspective view of the piece member in the ball screw, (B) is a back view, and (C) is a side view. It is a cross-sectional view which shows the attachment state to the nut of the same piece member. (A) And (B) is an expanded sectional view which shows each state before and after the pulling-out load of a piece member arm part is loaded. (A) And (B) is the nut longitudinal cross-sectional view and nut cross-sectional view which show the attachment state to the nut of the same piece member. (A) And (B) is each enlarged view of the a part and b part in FIG. (A) is a perspective view of the other example of a piece member, (B) is a back view, (C) is a front view. (A) And (B) is the nut longitudinal cross-sectional view and nut cross-sectional view which show the attachment state to the nut of the piece member in a prior art example. (A) And (B) is each enlarged view of the c section in FIG. 8, and the d section.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ball screw shaft 2 ... Nut 3 ... Ball 4 ... Piece member 5 ... Screw groove 6 of ball screw shaft ... Screw groove 7 of nut ... Rolling path 8 ... Connecting groove 9 ... Arm part 10 ... Clamping part 11 ... Piece Member fitting opening

Claims (3)

A ball screw shaft, a nut, a plurality of balls arranged in series with a rolling path formed between the screw grooves opposed to the ball screw shaft and the nut, and a connecting groove for connecting the screw grooves of the nut to each other; A plurality of piece members, and the piece members are fitted into a piece member fitting opening provided in the nut from the inner diameter side of the nut, and extend in opposite directions in the circumferential direction of the nut. in deflector type ball screw having a pair of a over arm portion for positioning which engages with the screw groove of the upper Symbol nut Te,
The cross-sectional shape of the arm part and a substantially circular, the arm portions extend in an arcuate shape along the thread groove of the nut, the outer peripheral surface of the arm portion of this, along the groove width center of the screw groove of the nut The radius of curvature of the arc is made larger than the radius of curvature of the groove width center on the inner surface of the screw groove of the nut, and the position where the arm portion and the inner surface of the screw groove of the nut are in contact with each other at no load is the tip of the arm portion. A top type ball screw characterized in that, when a pull-out load is applied to the piece member, the arm portion comes into contact with the inner surface of the thread groove of the nut along the circumferential direction .   The top ball screw according to claim 1, wherein the piece member is a sintered body obtained by granulating a kneaded material of metal fine powder and a binder, injection-molding the granulated material, and sintering.   3. The top-type ball according to claim 1 or 2, wherein the piece member is provided with a pair of protruding piece-like swaged portions that are swaged to the rim of the nut outer diameter side of the piece member fitting opening of the nut. screw.

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