JP3929747B2 - Ball screw - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing structure for an attachment member such as a dustproof seal attached to a nut of a ball screw.
[0002]
[Prior art]
A ball screw has a plurality of balls arranged between a spiral ball groove provided on an outer peripheral surface of a screw shaft and a spiral ball groove provided on an inner peripheral surface of a nut externally fitted on the screw shaft. The rotational power of the shaft (or nut) is converted into thrust of the nut (or screw shaft) via the ball. When such a ball screw is applied to a machine tool, for example, if foreign matter such as cutting waste or cutting oil adheres to the screw shaft and enters the nut during operation, wear of the ball or ball groove increases, resulting in malfunction. This may lead to a decrease in the life of the ball screw. In order to prevent this and to prevent leakage of the lubricant filled in the nut, generally, a dustproof seal is fixedly attached to the nut of the ball screw.
[0003]
As a structure for fixing a seal to a conventional ball screw nut, for example, a structure as shown in FIG. 5 is known. This is because a large-diameter step portion 53 for attaching a seal is formed at both ends of a ball screw nut 52 screwed to the ball screw shaft 50 via a ball 51, and on the inner peripheral surface of the large-diameter step portion 53. An open radial screw hole 54 is formed. That is, one or two radial screw holes 54 penetrating from the outer peripheral surface 52a of the ball screw nut 52 and the peripheral surface of the flange (not shown) to each large-diameter stepped portion 53 are formed. The depth dimension of the large-diameter step portion 53 is the same as the width dimension of the seal 55, and after the seal 55 is fitted thereto, the set screw 56 is fastened to the screw hole 54, so that the seal 55 is circumferentially and axially It is a structure fixed to.
[0004]
However, in the conventional nut seal fixing structure shown in FIG. 5, the seal 55 is fixed by a set screw 56 screwed into the screw hole 54, so that the screw hole 54 is processed in the ball screw nut 52. In order to secure the fixing of the seal 55, the screw holes 54 must be provided at two locations in the circumferential direction. It took time and effort to reduce the productivity.
[0005]
As a simple fixing structure that does not require such laborious screw hole processing, there is a structure as shown in FIGS. (B) is an enlarged view of part A of (a). This is because a large-diameter step portion 63 to which a seal 65 is attached is formed on at least one end portion of a nut 62 screwed to the screw shaft 60 via a ball 61, and the large-diameter step portion 63 is formed on the inner peripheral surface of the large-diameter step portion 63. A radial through hole 64 is formed, and a radial pin insertion hole 66 is provided on the peripheral surface of the seal 65 corresponding to the through hole 64. An engaging recess 67 is provided at a location where the through hole 64 and the pin insertion hole 66 are connected.
[0006]
On the other hand, as shown in FIG. 6 (c), the pin member 68 is provided with a convex portion 69 on the body portion, and a slit 70 is formed in one portion, whereby the pin member 68 is easily elastically deformed to enter the through hole 64. The pin 65 is inserted and engaged with the pin insertion hole 66 to fix the seal 65, and the projection 69 is engaged with the engagement recess 67 to prevent the pin member 68 from coming off (Japanese Patent Laid-Open No. Hei 6). -213299).
[0007]
[Problems to be solved by the invention]
However, the conventional nut seal fixing structure shown in FIG. 6 eliminates the need for laborious processing of screw holes, but it is still necessary to provide radial through holes 64 at two locations on the nut 62. The problem that improvement was difficult remained.
[0008]
The present invention has been made in view of the above circumstances, and does not require the time-consuming through-hole processing as in the prior art, the processing of the nut is simple, and the seal can be easily attached and removed. The object is to provide a cost-effective ball screw.
[0009]
[Means for Solving the Problems]
In order to achieve such an object, the invention according to claim 1 of the present invention includes a screw shaft having a spiral thread groove formed on the outer peripheral surface thereof, and a screw thread that is externally fitted to the screw shaft and has a helical screw thread on the inner peripheral surface thereof. A nut formed with a groove, a plurality of balls accommodated in a rolling path formed by opposing screw grooves, and a large-diameter step formed on the inner periphery of the end of the nut, and the screw groove of the screw shaft In the ball screw provided with a mounting member having an inner periphery with a protrusion that engages with a predetermined gap, an annular recess extending in the radial direction is formed at the bottom of the large-diameter step, and the large-diameter step The mounting member is loosely fitted through a predetermined radial clearance, and a pin is press-fitted into the radial clearance, and the tip of the pin is plastically deformed to engage with the annular recess.
[0010]
In this way, the pin can be prevented from coming off simply by press-fitting the pin into the radial clearance between the large-diameter step portion having the annular recess formed in the bottom portion and the attachment member loosely fitted in the large-diameter step portion. This eliminates the need for laborious through-hole processing, etc., as in the past, makes it easy to process nuts, and allows easy installation and removal of seals to provide a low-cost ball screw. be able to.
[0011]
Further, as in the invention described in claim 2, by providing a roundness at the tip of the pin, when the pin is press-fitted, the tip is easily deformed to the annular recess side of the large-diameter stepped portion, and this annular recess is surely formed. The tip can be engaged with the pin to prevent the pin from coming off, and the reliability can be improved.
[0012]
Further, if the tip of the pin is formed in a spire shape as in the invention described in claim 3, the tip of the pin is more likely to be deformed toward the annular recess of the large-diameter stepped portion, and the reliability is improved.
[0013]
In addition, if the slit is formed on the outer periphery of the tip end portion of the pin as in the invention described in claim 4, the tip is easily plastically deformed, so that the material of the pin is not restricted, and is made of a strong metal. You can also
[0014]
Preferably, as in the invention described in claim 5, by forming a convex portion at the base end portion of the pin, the removal operation of the pin is further simplified.
[0015]
Further, as in the invention described in claim 6, if the pins are press-fitted in at least three locations in the circumferential direction, the mounting member can be stably fixed. Sex can be maintained.
[0016]
Further, as in the invention described in claim 7, if a recess extending in the axial direction is formed on the outer periphery of the mounting member, and the pin is press-fitted between the inner diameter of the recess and the large diameter step portion, The radial clearance between the large-diameter stepped portion and the mounting member can be made as small as possible, and the sealing performance in the nut can be improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a ball screw according to the present invention will be described below in detail with reference to the drawings of FIGS. FIG. 1 is a longitudinal sectional view showing an embodiment of a ball screw according to the present invention.
[0018]
This ball screw includes a screw shaft 1 and a nut 2 fitted on the screw shaft 1, a spiral thread groove 3 provided on the outer peripheral surface of the screw shaft 1, and a spiral provided on the inner peripheral surface of the nut 2. A plurality of balls B are arranged in the rolling path formed by the threaded grooves 4. Seals 5 are attached to both ends of the nut 2 to prevent leakage of the lubricant filled in the nut 2 and entry of foreign matter from the outside. The seal 5 has a spiral protrusion 6 that engages with the screw groove 3 of the screw shaft 1 on the inner periphery. The projecting portion 6 is formed in a cross-sectional arc shape along the shape of the screw groove 3, and is opposed to the screw groove 3 through a slight gap to constitute a non-contact seal.
[0019]
The nut 2 has a mounting flange 7 at one end, and an annular large-diameter stepped portion 8 for mounting the seal 5 is formed on the inner periphery of both ends. The inner diameter of the large-diameter step portion 8 is slightly larger than the outer diameter of the seal 5, and the seal 5 is loosely fitted through a radial clearance. The large-diameter step portion 8 has substantially the same width as the width of the seal 5 or has a slightly larger depth, and annular recesses 8a and 8b extending in the radial direction are formed at the bottom and the opening. .
[0020]
The nut 2 is made of case-hardened steel such as SCM430, and a hardened layer having a predetermined hardness is formed on the entire surface including the screw groove 4 by carburizing and quenching. The nut 2 may be formed of medium carbon steel such as S55C, and a hardened surface layer by high frequency induction heating may be formed only in a portion such as the screw groove 4 that requires hardness.
[0021]
The screw shafts 3 and the screw grooves 3 and 4 formed in the nut 2 have a semicircular arc shape or a gothic arc shape, and are in angular contact with the ball B. Further, after rolling the rolling path formed by the spiral thread groove 3 provided on the outer peripheral surface of the screw shaft 1 and the spiral thread groove 4 provided on the inner peripheral surface of the nut 2 twice and half times, A ball circulation tube (not shown) that circulates the ball B across the rolling path is attached to the outer periphery of the nut 2, and the ball B moves into the rolling path during the relative helical movement of the screw shaft 1 and the nut 2. When rolling along the screw shaft 1 and turning twice and half, the ball circulation tube is scooped up at the tip of the ball circulation tube, moves inside the tube, and repeats the circulation motion to return to the original position. The ball circulation system is not limited to such a tube system, but is mounted on the inner periphery of the nut, a system using a piece member having a part of a thread groove, or an end cap having a ball reversing part is mounted on the end of the nut. It may be a method.
[0022]
The seal 5 is made of a synthetic resin such as PA 66 (polyamide 66), and is formed into a desired shape and size by injection molding. In addition, you may form with what is called a solid lubricating composition which lubricated lubricating components, such as lubricating oil and grease, to the base material for ultra high molecular weight polyolefin. Specifically, 5 to 99 wt% of a lubricating component is mixed with 95 to 1 wt% of ultrahigh molecular weight polyolefin powder, this mixture is put into a mold having a predetermined shape, and heated at a temperature equal to or higher than the gelation temperature of the ultrahigh molecular weight polyolefin. Then, it is formed by cooling and solidifying. The ultra-high molecular weight polyolefin powder is a powder composed of polyethylene, polypropylene, polybutene, or a copolymer thereof, or a mixed powder in which individual powders are blended, and each powder has an average molecular weight of about 1 × 10 ^{6 to} 5 × 10. ⁶ can be used.
[0023]
Next, the pin 9 for fixing the seal 5 will be described with reference to FIG. The pin 9 includes a body portion 10 having a rectangular cross section, a tip portion 11 having a spire shape, and a circular base end portion 12 protruding from the body portion 10. The distal end portion 11 is formed in a steeple shape in which one side is inclined from the central portion of the body portion 10 toward the distal end and the corner portion is rounded. When the pin 9 is press-fitted into the radial gap of the large-diameter step portion 8 of the nut 2 and the seal 5, the tip of the pin 9 comes into contact with the bottom portion of the large-diameter step portion 8 and further press-fits, so that the annular recess 8a is plasticized. Deforms and engages with the annular recess 8a. On the other hand, the base end portion 12 is accommodated in an annular recess 8b formed in the opening of the large diameter step portion 8 so as not to protrude from the end face of the nut 2, and when the seal 5 is removed, It can be pulled out with a simple jig. The pin 9 is molded into a suitable shape and is made of an injection moldable synthetic resin excellent in mass productivity.
[0024]
FIG. 3 shows another embodiment of the pin. The pin 13 includes a barrel portion 14 having a rectangular cross section, a tip portion 15 having a spire shape, and a circular base end portion 17 protruding from the barrel portion 14 and has substantially the same shape as the pin 9 described above. However, the difference is that the metal wire is press-molded and the slit 16 is formed from the body portion 14 to the tip portion 15. The slit 16 becomes a starting point at which the tip 15 is bent, and the tip 15 is easily plastically deformed when the pin 13 is press-fitted.
[0025]
FIG. 4 shows another embodiment of the seal. This seal 20 has a spiral projection 21 that engages with the thread groove 3 of the screw shaft 1 on the inner periphery, has substantially the same shape as the seal 5 described above, but is a recess extending in the axial direction on the outer periphery. The only difference is that 22 is provided. By inserting a pin 9 or 13 for fixing a seal between the inner diameter of the recess 22 and the large-diameter step portion 8, a radial clearance between the large-diameter step portion 8 formed in the nut 2 and the seal 20 is made as much as possible. Therefore, the sealing performance in the nut 2 can be improved.
[0026]
Since such a seal has a structure in which the seal is loosely fitted to a large-diameter step formed on the nut via a predetermined radial clearance, the seal itself is eccentric, and the protrusion on the inner periphery is the thread groove of the screw shaft. There is a risk that it will be in contact with and wear, and further the rotational torque of the ball screw will increase. Therefore, it is desirable to press-fit the fixing pins in at least three places on the circumference.
[0027]
This type of seal has a spiral protrusion on the inner periphery, and this protrusion is engaged with the thread groove of the screw shaft through a slight radial clearance. Can be attached to the large-diameter step portion of the nut by rotating the seal itself. Therefore, no load is applied to the seal in the rotational direction, and the seal can be prevented from falling off as long as the seal is positioned and fixed in the axial direction.
[0028]
The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.
[0029]
【The invention's effect】
As described in detail above, the ball screw according to the present invention can prevent the pin from being detached and can fix the mounting member only by press-fitting the pin. Therefore, the nut can be easily processed, and the seal can be easily attached and detached, so that a low-cost ball screw can be provided. Furthermore, if the pins are press-fitted in at least three locations along the circumference, stable sealing positioning can be achieved. Therefore, the clearance between the seal and the thread groove can be maintained constant, and stable rotational torque and sealing performance can be maintained for a long time.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of a ball screw according to the present invention.
FIG. 2A is a front view showing an embodiment of a pin in a ball screw according to the present invention.
(B) is a side view of (a).
FIG. 3A is a front view showing another embodiment of the pin in the ball screw according to the present invention.
(B) is a side view of (a).
FIG. 4 is a longitudinal sectional view showing another embodiment of the seal in the ball screw according to the present invention.
FIG. 5 is a longitudinal sectional view showing a conventional ball screw.
FIG. 6A is a longitudinal sectional view showing a conventional ball screw.
(B) is principal part sectional drawing to which the A section of (a) was expanded.
(C) is a front view of a pin member.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Screw shaft 2 ... Nuts 3, 4 ... Screw grooves 5, 20 ... Seals 6, 21 ... Projection Part 7 ... Mounting flange 8 ... Large diameter step 8a, 8b ... Ring recess 9, 13 ... Pins 10, 14, ... Body part 11, 15... Tip part 12, 17... Base end part 16... Slit 22. 61 ... Balls 52, 62 ... Nuts 53, 63 ... Large diameter step 54 ... Screw holes 55, 65 ... Seal 56 ...・ Set screw 64... Through hole 66... Pin insertion hole 67 ..engagement recess 68. ... Convex part 70 ... Slit B ....... ball

Claims (7)

In a rolling path formed by a screw shaft formed with a helical thread groove on the outer peripheral surface, a nut externally fitted to the screw shaft and formed with a helical thread groove on the inner peripheral surface, and both opposing screw grooves A mounting member having a plurality of balls housed in a nut and a projection that is attached to a large-diameter step formed on the inner periphery of the end of the nut and engages with a thread groove of the screw shaft via a predetermined clearance. In a ball screw with
An annular recess extending in the radial direction is formed at the bottom of the large-diameter step portion, and the mounting member is loosely fitted to the large-diameter step portion through a predetermined radial clearance, and a pin is press-fitted into the radial clearance. A ball screw characterized in that the tip of the pin is plastically deformed and engaged with the annular recess. The ball screw according to claim 1, wherein a tip of the pin is rounded. The ball screw according to claim 1 or 2, wherein a tip of the pin is formed in a spire shape. The ball screw according to any one of claims 1 to 3, wherein a slit is formed on an outer periphery of a tip portion of the pin. The ball screw according to claim 1, wherein a convex portion is formed at a base end portion of the pin. The ball screw according to any one of claims 1 to 5, wherein the pins are press-fitted in at least three locations in a circumferentially equidistant manner. The ball screw according to any one of claims 1 to 6, wherein a concave portion extending in an axial direction is formed on an outer periphery of the mounting member, and the pin is press-fitted between the concave portion and the inner diameter of the large diameter stepped portion.

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