JP2012062924A - Ball screw device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a disorder accompanying operating-torque fluctuation by reducing the same.SOLUTION: A supply hole 37 having a size of 50% or less of the outer diameter of a ball is formed near the intermediate passage of a bypass of a circulation piece 30. A pipe joint 40a is connected with a back 33 of the circulation piece 30 and other pipe joints not illustrated are collectively connected with a grease supply pump not illustrated, and grease is continuously supplied from the supply hole 37 through the pipe 41. This gives a low-friction condition in which an oil film is always formed in an endless circulation circuit, reducing the influence of friction on the ball. A ball clogging phenomenon is thus suppressed, resulting in reduction of the operating-torque fluctuation.

Description

The present invention relates to an improvement in the operability of a circulation piece type ball screw.

This has the problem of reducing operating torque fluctuations.

As a prior art for improving this part, there is a ball screw device disclosed in Japanese Patent Application Laid-Open No. 2003-314658. This is because the number N of balls 70 arranged in a circulation track as shown in FIG. The number of the separators 78 is one to three less than the maximum number that can be arranged on the pitch circle C projected in the axial direction, and the width of the separator 78 is a ball when N balls 70 are arranged at equal intervals on the pitch circle C. The size of the gap between 70 is set. In this way, a ball screw device that reduces torque fluctuation and operates smoothly is obtained.

JP 2003-314658 A

However, this prior art may cause the following problems as a ball screw used in a machine tool that requires high-precision machining.

In recent years, there has been a problem that a striped pattern is generated on a processed surface of a mold in the mold processing at a high-precision machining center, and the present inventor has conducted various experiments to find out the cause.

In that experiment, an experiment was conducted using a separator-equipped ball screw as disclosed in Japanese Patent Application Laid-Open No. 2003-314658 (Patent Document 1). I understand. It has been found that the occurrence of the striped pattern on the processed surface is caused by fluctuations in the operating torque. Therefore, even if the ball screw described in Patent Document 1 is adopted, the effect of reducing the generation of the striped pattern is not expected to be so much. There was a problem. The present invention has been made to solve such a problem, and an object of the present invention is to provide a ball screw device that can reduce the operating torque fluctuation and reduce the problems associated with the operating torque fluctuation.

In order to solve the above problems, the present invention has a screw shaft having a helical thread groove on the outer peripheral surface and a thread groove facing the screw groove of the screw shaft on the inner peripheral surface, and is screwed into the screw groove. Fixed to the nut to form a ball circulation circuit for infinite circulation of a nut to be joined, a large number of balls loaded in a rollable manner between the screw grooves, and a ball that rolls between the screw grooves. In the ball screw device provided with the circulation piece, the circulation piece has a function of continuously supplying oil and fat to the ball circulation circuit.

ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that it can prevent the malfunction accompanying operating torque fluctuation | variation, for example, that a striped pattern generate | occur | produces on the surface of the workpiece by a high precision machining center.

It is a figure which shows the perspective view which shows the structure of a circulation piece type | formula ball screw. The partial top view of the nut of a circulation top type ball screw is shown. The perspective view of a circulation top is shown. The structure figure of a circulation top is shown. The arrangement | positioning of the circulation piece which concerns on this invention is shown. The usage method of the ball screw of this invention is shown. The figure which projected and looked at the circulation track | orbit of the ball screw mechanism described in patent document 1 to the axial direction is shown.

An embodiment of a method for using a ball screw according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing the structure of a circulating top ball screw that is an object of the present invention. FIG. 2 is a partial cross-sectional view of the nut of the circulating top ball screw. FIG. 3 is a perspective view of the circulation piece.

As shown in FIGS. 1 and 2, the circulation piece type ball screw 110 has a circulation piece 30 as a circulation part on the inner peripheral surface of the nut 112. The bypass passage 32 provided in the circulation piece 30 connects both ends of the spiral rolling element raceway groove 22 formed by the screw groove 116 of the screw shaft 114 and the screw groove 20 of the nut 112 facing each other. Constitute. A large number of balls B are filled in the infinite circulation circuit 24, and the balls B circulate infinitely in the infinite circulation circuit 24.

Next, the configuration of the circulation piece 30 will be described with reference to FIGS. The upper surface 31 of the circulation piece 30 is an elongated oval surface, is curved with a curvature corresponding to the curved surface forming the inner peripheral surface of the nut 112, and is the same height as the screw thread 21 on the inner peripheral surface of the nut 112. In position. The height of the circulation piece 30 is larger than the diameter of the rolling element B. A groove forming a bypass path 32 is formed on the upper surface 31, and is continuous from the entrance / exit 34 a at one end of the circulation piece 30 to the entrance / exit 34 b at the other end. The cross-section of the bypass path 32 is U-shaped, and the bottom of the bypass path 32 is a curved surface corresponding to the spherical surface of the rolling element B.

The bypass path 32 includes an entrance / exit passage 36a on the entrance / exit 34a side, an entrance / exit passage 36b on the entrance / exit 34b side, and an intermediate passage 38 connecting the entrance / exit passages 36a and 36b.

The entrance / exit passage 36a and the entrance / exit passage 36b are greatly curved on the upper surface 31 and have a shape in which the letter S is reversed. Further, the entrance / exit 34 a is continuous with one end of the rolling element rail groove 22, and the entrance / exit 34 b is continuous with the other end of the rolling element rail groove 22. From one end of the rolling element raceway groove 22 to the other end, almost one turn is made along the outer periphery of the screw shaft 114. Between the entrance 34a and the entrance 34b, the screw thread 118 of the screw shaft 114 and the screw of the nut There is one mountain 21 each. The intermediate passage 38 is gently curved toward the outer periphery of the nut 112 so as to get over the thread 118 between the entrance 34a and the entrance 34b.

Then, the ball B moves to one end of the rolling element raceway groove 22, enters the entrance / exit passage 36 a through the entrance / exit 34 a, and enters the intermediate passage 38 with its traveling direction bent along the entrance / exit passage 36 a. The ball B entering the intermediate passage 38 gets over the thread 118 along the intermediate passage 38 and enters the entrance / exit passage 36b. The ball B travels along the entrance / exit passage 36b with its traveling direction bent, and passes through the entrance / exit 34b. Return to the other end of 22. The circulation piece type ball screw 110 has a plurality of infinite circulation circuits 24 including the rolling element raceway groove 22 and the bypass path 32 in the circulation piece 30.

As described above, the bypass passage 32 of the circulation piece 30 has a complicated passage shape combining the S-shape and the U-shape, has a severe bend R, and the passage width is set slightly larger than the outer diameter of the ball. Therefore, when the ball B passes, there may be a plover arrangement, and since the bypass path 32 is open to the inside of the nut 112, the ball B passing through the bypass path 32 and the screw shaft 114 come into contact with each other. There is a case. Due to these strict conditions, when the ball B passes through the bypass path 32 of the circulation piece 30, its movement tends to be irregular. Further, when the balls B pass through the endless circulation circuit 24 in series, the balls B are in contact with the balls arranged before and after the balls B, and the movements are regulated from each other due to the influence of friction at the contact portion, This also causes irregular movement of the ball B.

Irregular movement of the ball B in the circulation piece 30 causes clogging of the ball in the infinite circulation circuit 24 and causes fluctuations in the operating torque.

A supply hole 37 is provided in the vicinity of the intermediate passage 38 of the bypass passage 32 of the circulation piece 30 and the size thereof is 50% or less of the outer diameter of the ball B. A pipe joint 40 a is connected to the back surface 33 of the circulation piece 30, and another pipe joint 40 b (not shown) is centrally connected to an oil and fat supply pump (not shown), and the oil and fat is continuously supplied from the supply hole 37 through the pipe 41. As a result, the inside of the infinite circulation circuit 24 is always in a low friction state in which an oil film is formed, and the influence of friction on the ball B is reduced, so that the occurrence of the ball clogging phenomenon is suppressed and the fluctuation in operating torque is reduced.

Since the circulation piece 30 exists on the inner peripheral surface of the nut 112, the outer diameter of the nut 112 is reduced, and the circulation piece type ball screw device 110 having a compact structure can be obtained.

As shown schematically in FIG. 5, the plurality of circulation pieces 30 are all arranged at equal intervals in the circumferential direction with their positions shifted in the axial direction of the nut 112.

As shown in FIG. 6, the ball screw 110 is supported at both ends by the support unit 50 so as to be rotatable and non-movable in the axial direction, with the screw shaft 114 disposed in the horizontal direction. On the other hand, the nut 112 is fixed to the movable table 51 which is a mating member in a state in which the plurality of circulating pieces 30 are displaced in the axial direction of the nut 112 and are equally arranged in the circumferential direction.

One end of the screw shaft 114 is connected to the output shaft of the motor 52 and is rotated by the motor 52.

By the rotation of the screw shaft 114, the moving table 51 fixed to the nut 112 and guided by the linear guide device 53 moves along the longitudinal direction of the screw shaft 114.

According to the ball screw device of the present invention, by constantly supplying oil and fat into the infinite circulation circuit, the frictional resistance in the ball circulation circuit is reduced, so that the occurrence of clogging of the ball can be suppressed. Accordingly, fluctuations in the operating torque can be reduced, and problems associated with fluctuations in the operating torque, such as the occurrence of striped patterns generated on the workpiece surface of the machine tool, can be solved.

The present invention can be widely applied to various mechanical devices as a ball screw device having a circulation piece.

20 Thread groove (nut side) 24 Infinite circulation circuit 30 Circulation piece 32 Bypass path 40a Piping joint 51 Moving table 112 Nut 114 Screw shaft 116 Thread groove (screw shaft side) B Ball

Claims (1)

A screw shaft having a helical thread groove on the outer peripheral surface, a nut having a thread groove facing the screw groove of the screw shaft on the inner peripheral surface and screwed into the screw groove, and between the two screw grooves A ball screw device comprising a plurality of balls loaded in a rollable manner and a circulation piece fixed to the nut so as to form a ball circulation circuit for infinite circulation of the balls rolling between the two screw grooves. The circulation piece has a function of continuously supplying oil and fat to the ball circulation circuit.

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