JP6007653B2 - Ball screw device - Google Patents

Description

  The present invention relates to a ball screw device that can be suitably used for conveyance and precision positioning of machine tools, industrial machines, etc., and more particularly to a preload structure of a double nut ball screw device.

  As a double nut ball screw device, for example, a technique described in Patent Document 1 is disclosed. The ball screw device described in the document includes a single screw shaft and two nuts that are paired with the screw shaft. A flat spacer is inserted between the two nuts (a spacer thicker or thinner than the gap between the nuts by a preload amount is inserted). Thereby, according to the ball screw device of the literature, a preload can be given to a nut.

JP 2004-257466 A

However, since the flat spacer is in surface contact with each end face of the two nuts, the two nuts that are paired are not only restricted in the axial direction but also restricted in the radial direction. Therefore, depending on the degree of assembly, a relative misalignment error or an inclination error occurs between the nuts, and thereby the load balance of the rolling balls incorporated in the nuts is lost. For this reason, there is a problem that the operability of the ball screw is deteriorated. In other words, since the load distribution is not constant, there is a problem that the preload applied to the rolling ball varies depending on the location.
Therefore, the present invention has been made paying attention to such problems, and an object thereof is to provide a double nut type ball screw device that has good operability and easy preload adjustment work. .

In order to solve the above-described problems, a ball screw device according to an aspect of the present invention includes a screw shaft, and two nuts screwed to the screw shaft via rolling balls that roll a ball screw groove. A ball screw device including a preload applying means for applying a pre-loaded axial force to each nut, and the preload applying means is interposed between the two nuts. Three or more balls, a ball holder having a plurality of storage portions having openings toward the outer periphery so that the three or more balls can be received, and openings of the plurality of storage portions of the ball holder A plurality of lid members that are closed from the direction, and the ball holder is mounted between the two nuts in a state in which the thickness direction of the ball holder is directed in the axial direction, and the three or more the thickness than the outer diameter of the ball and is thinner, the ball A plurality of accommodating portions of the lifting device, characterized in that it is formed of the three or more balls in the circumferential direction of itself to distribution substantially equal.

Here, in the ball screw device according to an aspect of the present invention, it is preferable that the plurality of storage units include one ball or a plurality of balls stored in each storage unit.
In the ball screw device according to one aspect of the present invention, it is preferable that the ball holder has the plurality of accommodating portions formed in three places.
In the ball screw device according to one aspect of the present invention, the outer diameter of the ball used for the preload applying means is the same nominal size as the outer diameter of the rolling ball that rolls in the ball screw groove. preferable.

According to the present invention, the plurality of balls housed in the plurality of housing portions equally arranged on the ball holder can abut against the nut end face and give a preload. Therefore, the two nuts that form a pair are only restrained in the axial direction and not in the radial direction. Each ball rolls in the radial direction of the nut to adjust the position of both nuts. Therefore, no relative misalignment error or tilt error occurs between the nuts. As a result, according to the present invention, a stable preload is applied to the rolling balls incorporated in both nuts, so that the operability of the ball screw device is not affected.
Further, in the ball holder, the plurality of housing portions have openings on the outer periphery so that the balls can be accommodated, and the openings are closed by the lid member. The balls can be exchanged from the outer diameter side with the individual nuts close to each other, and the assemblability is improved.

  In other words, the conventional flat spacer has a problem in that after the spacer is once assembled to the ball screw and the degree of preload is checked, the spacer is removed again and the thickness is adjusted by grinding. . On the other hand, according to the present invention, since a plurality of balls are used instead of the flat spacers, they can be replaced with balls having different diameters depending on the degree of preload. Therefore, it is not necessary to grind the spacer, so that the work process is simplified. In general, balls of different sizes are prepared in advance at the assembly process site of the ball screw. Therefore, since it is not necessary to prepare a new ball, it is convenient for facilitating the preload adjustment work. Here, if the outer diameter of the ball used for the preload applying means is the same nominal size as the outer diameter of the ball rolling in the ball screw groove, it is preferable because the number of types of components does not need to be increased.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of one Embodiment of the double nut type ball screw apparatus which concerns on 1 aspect of this invention, The figure (a) is sectional drawing along the axial direction of the screw shaft, (b) is a cross-sectional view. . It is explanatory drawing of one Embodiment of the preload provision means which concerns on this invention, The figure (a) is a front view of a preload provision means, (b) is XX sectional drawing in the figure (a). It is explanatory drawing (the figure corresponding to Fig.2 (a)) of the modification (1st modification) of the preload provision means shown in FIG. It is explanatory drawing (the figure corresponding to FIG. 2 (a), (b), respectively) of the modification (2nd modification) of the preload provision means shown in FIG. It is explanatory drawing (the figure corresponding to Fig.2 (a)) of the modification (3rd modification) of the preload provision means shown in FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate.
As shown in FIG. 1, the ball screw device 10 of the present embodiment employs a double nut preload system. The ball screw device 10 includes a single screw shaft 1 and a first nut 3 a and a second nut 3 b that are screwed to the screw shaft 1 via steel balls 2 that are a plurality of rolling balls. Have. A ball rolling groove 9 is spirally formed on the outer peripheral surface of the screw shaft 1.

  The first nut 3 a and the second nut 3 b are formed in a cylindrical shape with an inner diameter larger than the outer diameter of the screw shaft 1. An annular flange is formed at one end of the first nut 3a. Ball rolling grooves 8 facing the ball rolling grooves 9 of the screw shaft 1 are formed on the inner peripheral surfaces of the nuts 3a and 3b. A plurality of steel balls 2 are interposed in a rolling path formed by the ball rolling groove 9 of the screw shaft 1 and the ball rolling groove 8 of the nuts 3a and 3b so as to be able to roll.

  The two nuts 3a and 3b are positioned in the rotation direction by a key (not shown) inserted through the key groove 5 so that the phase in the rotation direction is not shifted. End deflectors (not shown) are fitted into both end faces of the nuts 3a and 3b. The end deflector communicates with the through holes 4a and 4b connecting both end surfaces of the nuts 3a and 3b to form a guide passage for the steel ball 2. The steel ball 2 that rolls between the ball rolling groove 9 of the screw shaft 1 and the ball rolling groove 8 of the nuts 3a and 3b moves up to one end of the nuts 3a and 3b, and then scoops up the end deflector. Then, it passes through the through holes 4a and 4b and moves to the opposite end, and again enters between the ball rolling groove 9 of the screw shaft 1 and the ball rolling groove 8 of the nuts 3a and 3b by the end deflector. A circulation structure is formed that returns to the original state.

Here, in the conventional double nut preload type ball screw device, when preload is applied, a flat plate spacer is sandwiched between nuts, and the amount of preload is often adjusted by the thickness. In the example of this embodiment, the amount of preload is adjusted by changing the size of the plurality of balls 7 sandwiched between the nuts 3a and 3b.
In detail, in this embodiment, as shown in FIG. 1, it has the preload provision means 20 which applies the force of the axial direction opposite to each nut 3a, 3b, and gives preload. As shown in FIG. 2, the preload applying means 20 includes three balls 7 having the same diameter that are interposed between the two nuts 3 a and 3 b and used for preload adjustment, and three balls 7. A ball holder 6 having a plurality of receiving portions 6a each having an opening 6d facing the outer periphery so as to be able to be received, and a plurality of lid members 6b for closing the radial openings 6d of the plurality of receiving portions 6a. Yes.

  The three balls 7 used for preload adjustment use precision grade steel balls used as parts for bearings and ball screws, and basically use tempered steel balls. . However, a ball made of a material such as ceramic may be used as necessary. In general, these precision grade balls are prepared in a fine size with reference to the nominal size of the ball diameter. (For example, in the case of a 1/4 inch steel ball, balls are prepared every 0.5 to several μm in a range of ± 30 μm with a ball diameter of φ6.35 mm as a reference.)

  The ball holder 6 is a substantially ring-shaped member having a plate thickness thinner than the outer diameter of the three balls 7. This ball holder 6 is divided along a line segment CL passing through the center O of the screw shaft 1 so that the balls 7 can be easily replaced even when the two nuts 3a and 3b are assembled to the screw shaft 1. The divided structure is divided into left and right parts from the part 6e. The plurality (three in this example) of receiving portions 6a of the ball holder 6 are formed of U-shaped grooves formed so that the three balls 7 are arranged approximately three times in the circumferential direction thereof. A flat portion 21 is formed on the outer peripheral side of each accommodating portion 6a, and screw holes 23 for screwing set screws 22 for fixing the lid member 6b are provided on the left and right of each flat portion 21. ing.

  As a result, the lid member 6b can be mounted on the flat surface portion 21 by the set screw 22, and the ball 7 is prevented from dropping in the circumferential direction of the nuts 3a and 3b from within the housing portion 6a formed of a U-shaped groove. . The accommodating portion 6a arranged in a substantially equal distribution on the ball holder 6 has the opening 6d toward the outer periphery as described above, but the ball 7 is accommodated in the accommodating portion 6a from the opening 6d, and thereafter The lid member 6b is fastened to the opening 6d by the set screw 22 so that the opening 6d is fixed. With this structure, the ball 7 is held by the ball holder 6 while the first nut 3a and the second nut 3b are screwed to the screw shaft 1 via the steel balls 2 as a plurality of rolling balls. It is possible to insert and take out from the outer periphery.

  In addition, the escape part 6c for avoiding interference with the key groove 5 of nut 3a, 3b is formed in the concave shape in the position on the opposite side in the radial direction of the divided part 6e divided into two. As a result, the end surfaces of both nuts 3a and 3b can be positioned in parallel without rattling, and the three balls 7 are arranged in three equal spaces by each accommodating portion 6a so that the rigidity of the nuts 3a and 3b can be improved. It is possible to increase.

Next, the effect of the double nut type ball screw apparatus 10 of this embodiment mentioned above is demonstrated.
When assembling the double nut ball screw device 10 of the present embodiment described above, the first nut 3a and the second nut 3b are attached to the screw shaft 1 via the steel balls 2 as a plurality of rolling balls. It is assembled in a housing (not shown) while being screwed. In that case, first, the two nuts 3a and 3b which make a pair are brought close to each other, and the two divided ball holders 6 are sandwiched between the nuts 3a and 3b while facing each other in the radial direction. Next, the balls 7 are sequentially inserted into the respective accommodating portions 6a of the ball holder 6, and the lid member 6b is fixed to the flat surface portion 21 from the outside of the accommodating portion 6a with a set screw 22. Thereby, the preload applying means 20 can be interposed between the two nuts 3a and 3b.

  By the way, in the conventional double nut preloading type ball screw device, the spacer comes into surface contact with the two nut end faces, and therefore, when the spacer is sandwiched between the nuts and tightened in the axial direction, it comes into contact with the nut end face. However, a large frictional force was generated on both end surfaces of the spacer, and the contact surface could not be easily moved in the radial direction. For this reason, when the assembly starts in a state where the nut has a misalignment error or a tilt error, it becomes difficult to make adjustments in the middle of the nut. Therefore, even in the final assembly state, a misalignment error or a tilt error has occurred. Therefore, in the conventional double nut preload type ball screw device, the load balance of the steel balls incorporated in both nuts is disrupted and the load distribution is not constant, and the preload applied to the steel balls varies depending on the location. There is a problem that the operability of the ball screw is deteriorated.

  On the other hand, in the double nut type ball screw device 10 according to the present embodiment, the preload applying means 20 is sandwiched between the two nuts 3a and 3b in order to hold the ball holder 6 holding the three balls 7. Since the point contact is made at the contact portion between the three balls 7 and the end faces of the two nuts 3a and 3b, the ball 7 can roll in the radial direction. Thereby, according to this ball screw device 10, since the radial position of the nuts 3a and 3b can be easily adjusted, there is no misalignment error or tilt error even in the final assembly state, and the operability of the ball screw is deteriorated. There is no.

  In addition, in the conventional method of adjusting the preload using the spacer in the ball screw device of the double nut preloading method, after installing the spacer and confirming the preload, the spacer is removed again and the spacer is subjected to thickness adjustment such as double-side polishing. A process was required. On the other hand, the ball screw device 10 of the present embodiment incorporates a ball holder 6 containing three balls 7 between the two nuts 3a, 3b to check the preload state, Since the preload can be adjusted to the optimum preload by replacing the balls 7 having different external dimensions, the number of work steps can be greatly reduced.

  Here, it is desirable that the size of the ball 7 used for the preload adjustment is the same as that of the steel ball 2 rolling between the ball rolling grooves 8 and 9. That is, if the outer diameter of the ball 7 used for the preload applying means 20 is the same nominal size as the outer diameter of the ball 2 rolling on the ball screw grooves 8 and 9, it is not necessary to increase the number of types of components. It is. This is because a large number of steel balls 2 having different sizes are usually prepared in advance when assembling the ball screw. For this reason, such a configuration is convenient in that it is not necessary to prepare a new ball 7 having a different size for the preload adjusting ball 7, thereby greatly reducing the number of work steps.

As described above, the double nut type ball screw device 10 of the present embodiment is assembled by sandwiching the ball holder 6 containing the three balls 7 between the two nuts 3a and 3b. The operability of the ball screw device 10 is good, and preload adjustment is easy.
The double nut ball screw device according to the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the preload applying means 20 has been described as an example in which three balls 7 are equally arranged, but the present invention is not limited to this.

  For example, in the case of three-point support using three balls 7, if a large preload load or an external load is applied, or if the load per ball is excessive, the end face of the ball or nut may be damaged. is there. Therefore, in such a case, as a countermeasure, a configuration in which a plurality of balls 7 are arranged in each housing portion 6a for housing the balls 7 can be adopted. As a specific example, as shown in FIG. 3, a plurality of (two in each case) balls 7 can be accommodated in each accommodating portion 6a. With such a configuration, the load is distributed by installing more balls 7 (total of 8 in this example), and the load per ball is reduced. Therefore, it is possible to prevent the ball 7 and the end surfaces of the nuts 3a and 3b from being damaged.

  Further, for example, as in the second modification shown in FIG. 4, the plurality of accommodating portions 6 a can be four or more (equally arranged in four places in the circumferential direction in the example of the figure). Even with such a configuration, the load is distributed by installing more balls 7 (four in this example), and the load per ball is reduced, so the balls 7 and nuts 3a, 3b Breakage of the end face can be prevented.

Here, when three or more balls are sandwiched between the two nuts 3a and 3b in addition to the three balls 7 having the same diameter, the dimension between the nuts 3a and 3b is three. It is determined by the outer diameter of the ball 7. Therefore, the other balls can be in a free state where they are not restrained by the end surfaces of the nuts due to slight undulations of the end surfaces of the nuts and variations in the outer diameter of the balls. In this case, every time the ball screw device 10 is driven, another ball 7 may rattle and become a source of vibration and noise. Therefore, in such a case, it is desirable that the number of the plurality of balls 7 interposed between the nuts 3a and 3b is three as in the above embodiment.
In the above-described double nut type ball screw device 10, an example in which an end deflector is used for the circulation structure of the rolling ball 2 in the known circulation structure of the rolling element of the ball screw has been described. The structure of the ball screw is not limited to a tube type, a top type, or the like, and any circulation method can be used as long as the nut end face is a metal.

  Moreover, in the structure of the above-mentioned preload provision means 20, although it did not mention in particular about the greasing structure, for example like the 3rd modification shown in FIG. 5, the greasing structure is further provided to the preload provision means 20. be able to. In the example shown in the figure, the ball holder 25 is provided with a greasing hole 25 in one place. The greasing hole 25 is provided at a position between the accommodating portion 6a and the escape portion 6c in the circumferential direction. The greasing hole 25 is formed so as to penetrate from the outer peripheral surface of the ball holder 6 to the inner peripheral surface along the radial direction, and a female screw 25m is formed on the outer peripheral side. Accordingly, if oil or grease is supplied from the greasing hole 25, the ball holder 6 can be used more effectively, and the oil or grease is supplied from the preload applying means 20 at the center of the two nuts 3a and 3b to the ball. The entire nut of the screw device 10 can be supplied evenly.

  In any of the above-described embodiments or modifications, a gap may occur between the nuts 3a and 3b due to the configuration of the preload applying means 20, but in order to close the gap, A cover that covers a part of the nut including the gap portion can be attached. By providing such a cover member, it is possible to prevent entry of foreign matter or the like into the gap portion. Further, the periphery of the gap portion is sealed with a tape such as aluminum tape, the surface layer portion is sealed with a resin material such as silicon along the outer periphery of the preload applying means 20, or the surface layer portion is sealed by embedding a metal bond. You may do it.

1 Screw shaft 2 Steel ball (rolling ball)
3a, 3b Nut 4a, 4b Through hole 5 Key groove 6 Ball holder 6a Receiving part 6b Cover member 6c Escape part 6d Opening part 6e Dividing part 7 Ball 8 Ball rolling groove 9 (of screw shaft) Ball rolling Moving groove 10 Ball screw device 20 (double nut type) 20 Preload applying means 21 Planar portion 22 Set screw 23 Screw hole 25 Greasing hole

Claims (5)

A screw shaft, two nuts that are screwed onto the screw shaft via rolling balls that roll the ball screw groove, and a preload that applies pre-load by applying an axial force in the opposite direction to each nut. A ball screw device comprising means,
The preload applying means has three or more balls interposed between the two nuts, and a plurality of accommodating portions having openings toward the outer periphery so as to accommodate the three or more balls. A ball holder, and a plurality of lid members for closing the openings of the plurality of storage portions of the ball holder from the radial direction,
The ball retainer, while being mounted between each other the two nuts in a state where the direction of the thickness of its facing in the axial direction, said thickness than the outer diameter of said three or more balls A ball screw device, wherein the ball holding device is thin, and the plurality of receiving portions of the ball holder are formed so as to distribute the three or more balls substantially in the circumferential direction thereof.   2. The ball screw device according to claim 1, wherein each of the plurality of accommodating portions has one ball accommodated in each accommodating portion.   2. The ball screw device according to claim 1, wherein the plurality of accommodating portions includes a plurality of balls accommodated in the accommodating portions.   The ball screw device according to any one of claims 1 to 3, wherein the ball holder has the plurality of accommodating portions formed in three places. 5. The outer diameter of the ball used for the preload applying means is the same nominal size as the outer diameter of the rolling ball that rolls in the ball screw groove. 5. The ball screw device described.

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