JP2010025301A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw reduced in damage, vibration, and noise by smoothly changing balls in direction in an end cap by taking into consideration a locus viewed from a nut side at which the balls to be discharged are rotated. <P>SOLUTION: A direction converting passage 10 formed on the end surface of the end cap 3 is formed in a curve along a path through which the balls 4A, 4B moving in the rotating nut 2 are moved by receiving a Coriolis force F (F=2m[Vxω]) (path indicated by dashed line in the figure). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ball screw.

  As a ball screw, a screw shaft in which a male screw groove is formed, a nut having a female screw groove that forms a main passage so as to face the screw groove of the screw shaft, a plurality of balls that roll in the main passage, and a main passage What is provided with the ball | bowl circulation member which has a direction change path for circulating the ball | bowl inside is known.

The direction change path formed in the ball circulation member of the conventional ball screw is generally a straight line extending from the screw groove in the tangential direction when viewed from the axial direction (Patent Document 1), and from the screw groove in the tangential direction. One having a straight line portion that extends and a straight line portion bent with respect to the straight line portion has also been proposed (Patent Document 2).
JP 2004-36644 A JP 2004-84743 A

  In the above conventional ball screw, the straight line portion extending in the tangential direction in the direction change path is for guiding the ball released in the tangential direction, but is viewed from the rotating nut side. Since the trajectory is not a straight line in the tangential direction, the ball may collide with the wall of the direction change path, which may have an adverse effect on the direction change path damage and the generation of vibration and noise. There is.

  The object of the present invention is to smoothly change the direction of the ball in the direction change path by considering the trajectory when the released ball is viewed from the rotating nut side, thereby causing damage, vibration and noise. It is to provide a ball screw with reduced.

  A ball screw according to the present invention includes a screw shaft in which a male screw groove is formed, a nut having a female screw groove that forms a main passage so as to face the screw groove of the screw shaft, and a plurality of balls that roll in the main passage. And a ball screw having a ball circulation member having a direction change path for circulating the ball in the main passage, the direction change path of the ball circulation member is a curve whose diameter gradually increases when viewed from the axial direction. It is formed in the shape.

  The ball screw nut is, for example, an end cap type (a pair of end caps are provided on both end surfaces in the axial direction of the nut, and a return passage penetrating the peripheral wall on the radially outer side of the female screw groove is formed in the nut. A groove-shaped direction changing path that connects the main passage and the return passage is formed on the end surface on the nut side. The ball screw nut may be a recirculating top type or a tube type.

  In the conventional ball screw, the ball released in the tangential direction changes straight after traveling straight. On the other hand, in the ball screw according to the present invention, the ball released in the tangential direction moves along a curve without going straight. This curve is a curve that gradually increases in diameter in order to avoid a strong collision between the ball and the wall surface of the direction change path.

  More preferably, the direction changing path is a trajectory when the ball moving in the rotating nut receives the Coriolis force and moves.

  When viewed from an inertial coordinate system (for example, a housing supporting a ball screw), the ball released in the tangential direction goes straight in that direction. On the other hand, when viewed from the rotating coordinate system (on the nut), the ball advances in the direction in which it is released and also advances in the direction opposite to the nut rotation direction. In the rotating coordinate system, the mass of the ball is m, the angular velocity of the nut is ω, the discharge speed of the ball is V, and Coriolis force (2m [V × ω]: V × ω is a vector product) acts on the ball. Therefore, the trajectory of the ball that has received this Coriolis force can be obtained, and by using the direction change path as this trajectory, the ball smoothly enters the direction change path and collides with the wall of the direction change path. Proceed without any problems. As described above, the Coriolis force is determined by the rotation speed of the nut and the discharge speed of the ball, and since the discharge speed of the ball is proportional to the rotation speed of the nut, the rotation speed of the nut and the discharge speed of the ball Even if changes, the trajectory of the ball is unambiguously determined without changing. Therefore, the ball can move smoothly along the direction change path regardless of the rotation speed, which is very advantageous for avoiding damage to the direction change path and reducing vibration and noise.

  The screw shaft and nut are made of, for example, carbon steel such as S45C, S55C or SAE4150 steel, and the ball is made of bearing steel (SUJ2), for example. The nut may be made of bearing steel (SUJ2). The end cap is made of synthetic resin or steel.

  According to the ball screw of the present invention, the direction changing path is formed in a curved shape whose diameter gradually increases when viewed from the axial direction in consideration of a locus when the ball to be discharged is viewed from the rotating nut side. As a result, the ball can be smoothly turned, thereby reducing damage, vibration, noise, and the like caused by the ball strongly colliding with the wall surface of the turn path.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 is a longitudinal sectional view of a main part of the ball screw, FIG. 2 is a transverse sectional view thereof, and FIG. 3 is an enlarged transverse sectional view of FIG.

  The ball screw includes a steel screw shaft (1), a steel nut (2), a pair of synthetic resin end caps (ball circulation members) (3), and a large number of balls (4).

  The screw shaft (1) is a solid shaft having a circular cross section, and one screw groove (5) is formed on the outer peripheral surface of the screw shaft (1) over the entire length of the screw shaft (1).

  The nut (2) has a cylindrical shape and is fitted to the outer periphery of the screw shaft (1) with a slight gap in the radial direction. A single thread groove (6) corresponding to the male thread groove (5) is formed on the inner peripheral surface of the nut (2).

  The end cap (3) is made of a short cylindrical ring having the same shape, and is fixed to both end faces in the axial direction of the nut (2) using a connector such as a bolt (7).

The main path (ball path) (8) where the ball (4) rolls in the space between the female thread groove (6) of the nut (2) and the thread groove (5) of the screw shaft (1) facing this It has become. A return passage (9) is formed in one place on the peripheral wall of the nut (2). The return passage (9) is a through hole having a circular cross section that penetrates the nut (2) over the entire length in the axial direction.
A groove-shaped direction change path (10) for communicating the main passage (8) and the return passage (9) is formed on the end face of each end cap (3) on the nut (2) side. The direction changing path (10) is formed in a curved shape extending in the direction opposite to the rotation direction of the nut (2) and gradually increasing in diameter. On the inner peripheral side of the direction changing path (10), a ball scooping part (11) for scooping the ball (4) from the male thread groove (5) and guiding it into the direction changing path (10) is formed.

  The ball (4) is disposed in the main passage (8), the return passage (9) and the direction changing passage (10), and the ball (4) rolling in the main passage (8) is connected to the screw shaft (1). The relative rotation of the nut (2) is guided.

  When the screw shaft (1) and the nut (2) rotate relative to each other, the screw shaft (1) and the nut (2) relatively move in the axial direction. At this time, the ball (4) rolling in the main passage (8) is changed in direction by the direction change passage (10) of one end cap (3) and is returned to the return passage (9) of the nut (2). The ball (4) that has been introduced and moved in the return passage (9) to the other end cap (3) side and moved through the return passage (9) is directed to the direction change path (10 of the other end cap (3)). ) And is introduced into the main passage (8).

  In FIG. 3, the alternate long and short dash line shows the trajectory when the ball (4) moving in the rotating nut (2) (including the end cap (3)) moves under the Coriolis force. The shape of the path (10) is a curved line along this locus.

  When viewed from the inertial coordinate system, the ball (4A) released in the tangential direction goes straight in that direction. Therefore, the conventional end cap is provided with a direction changing path that linearly extends in the direction of the arrow, assuming that the ball (4A) advances straight in the tangential direction. On the other hand, when viewed from the rotating coordinate system (on the nut (2) or the end cap (3)), the ball (4A) released in the tangential direction advances in the released direction and the rotation direction of the nut (2) Proceed in the opposite direction. In the rotating coordinate system, for example, when considering a ball indicated by reference numeral (4B), the mass is m, the angular velocity of the nut (2) is ω, the discharge velocity of the ball (4) is V, and the ball (4B) Coriolis force F (= 2m [V × ω]: V × ω is a vector product) acts. As a result, the ball (4A) (4B) tries to move along the locus indicated by the alternate long and short dash line, and the shape of the direction change path (10) is along this locus, so the ball (4A) (4B) The wall surface of the direction change path (10) does not exert a force in a direction perpendicular to the wall surface (the balls (4A) and (4B) do not collide with the wall surface). The trajectory of the balls (4A) and (4B) that have received the Coriolis force can be obtained by calculation, and based on this, the direction change path (10) can be obtained. The Coriolis force is determined by the rotational speed (angular speed ω) of the nut (2) and the discharge speed V of the balls (4A) (4B). The discharge speed V of the balls (4A) (4B) is Since it is proportional to the angular velocity ω, even if the angular velocity ω of the nut (2) and the discharge velocity V of the balls (4A) (4B) change, the trajectory of the balls (4A) (4B) does not change. , It is decided uniquely. Therefore, the balls (4A) and (4B) can move smoothly along the direction change path (10) regardless of the rotation speed, which is very useful for avoiding damage to the end cap (3) and reducing vibration and noise. It will be advantageous.

  In addition, the shape of the direction change path (10) is a curved shape that approximates the trajectory of the ball (4A) (4B) that has received the Coriolis force, as compared to the conventional direction change path that extends linearly, The ball can move smoothly along the direction change path, which is advantageous in avoiding damage to the end cap and reducing vibration and noise. In the above description, the thread grooves (5) and (6) are one, but it goes without saying that the thread grooves may be multiple.

FIG. 1 is a longitudinal sectional view of a main part of a ball screw showing an embodiment of the present invention. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 3 is an enlarged view of a main part of FIG.

Explanation of symbols

(1) Screw shaft
(2) Nut
(3) End cap (ball circulation member)
(4) Ball
(5) Male thread groove
(6) Female thread groove
(8) Main passage
(10) Direction change path

Claims (2)

A screw shaft having a male thread groove, a nut having a female thread groove that forms a main passage so as to face the screw groove of the screw shaft, a plurality of balls that roll in the main passage, and a ball in the main passage In a ball screw comprising a ball circulation member having a direction change path for circulation,
A ball screw characterized in that the direction changing path of the ball circulation member is formed in a curved shape having a gradually increasing diameter when viewed from the axial direction.   2. The ball screw according to claim 1, wherein the direction changing path is a trajectory when the ball moving in the rotating nut receives the Coriolis force and moves.

Images