Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
2002-07-17
2004-08-17
Bucci, David A. (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S424710, C074S424810, C384S043000, C384S049000
Reexamination Certificate
active
06776063
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a ball screw for use in a machine tool and, especially, to a ball screw of a tube circulation type.
In a machine tool, as a mechanism for converting the rotation of a motor into a linear motion, there is used, for example, such a ball screw
10
as shown in
FIGS. 21 and 22
. This ball screw
10
is structured in the following manner. Namely, a screw shaft
11
includes a first spiral groove
12
formed in the outer peripheral surface thereof. In the inner peripheral surface of a nut
13
disposed on the outer periphery of the screw shaft
11
, there is formed a second spiral groove
14
such that it is opposed to the first spiral groove
12
. Also, in the ball screw
10
, between the first and second spiral grooves
12
and
14
, there are interposed a large number of balls
15
in such a manner that they are allowed to roll between them. In case where the screw shaft
11
is rotated, the balls
15
are allowed to roll between the first and second spiral grooves
12
and
14
due to a frictional force and, with the rolling motion of the balls
15
, the nut
13
is allowed to move in the axial direction of the screw shaft
11
.
By the way, to make the nut
13
of the ball screw
10
move continuously in the axial direction of the screw shaft
11
, the balls
15
must be rolled repeatedly between the first and second spiral grooves
12
and
14
. For this purpose, conventionally, there are formed, in the nut
13
, ball circulation holes
16
and
17
which are used to discharge the balls
15
from a rolling passage formed between the first and second spiral grooves
12
and
14
to the outside of the nut
13
or introduce the balls
15
into the rolling passage from the outside of the nut
13
, and, the two end portions of a ball circulation tube
18
are respectively inserted into these ball circulation holes
16
and
17
to thereby roll the balls
15
repeatedly. By the way, in
FIGS. 21 and 22
, reference character
19
designates a mounting metal member which is used to mount the ball circulation tube
18
onto the nut
13
.
However, in the above-mentioned conventional ball screw, as a ball circulation tube which forms a circulation passage for the balls
15
in the outside of the nut
13
, there is used such a ball circulation tube as shown in
FIG. 23
, that is, the ball circulation tube
18
whose section along the diameter direction thereof has a shape approximate to a circle and, therefore, as shown in
FIG. 24
, in the curved portions of the ball circulation tube
18
, the balls
15
are arranged in a line on the outside thereof. In the case of such ball arrangement, as shown in
FIG. 25
, due to the mutual sliding motion between the balls which occurs within the ball circulation tube
18
, the torque of the ball screw is caused vary, which has an ill influence on the operating performance of the ball screw.
SUMMARY OF THE INVENTION
The present invention aims at eliminating the drawbacks found in the conventional ball screw. Accordingly, it is an object of the invention to provide a ball screw which can prevent the torque to the ball screw from varying greatly due to the mutual sliding motion between the balls which occurs within the ball circulation tube.
The above object can be attained by a ball screw according to a first aspect of the present invention, comprising:
a screw shaft including a first spiral groove formed in the outer peripheral surface thereof;
a nut disposed on the outer periphery of the screw shaft, said nut having a second spiral groove formed in its inner peripheral surface in such a manner that it is opposed to the first spiral groove;
a number of balls rollably held by and between the second spiral groove and first spiral groove; and,
a ball circulation tube for forming a circulation passage for the balls in the outside of the nut,
wherein the ball circulation tube has such a shape that the movable amount of the balls in a first direction intersecting at right angles to the axis of the ball circulation tube is larger than the movable amount of the balls in a second direction intersecting at right angles to the first direction, and the ball circulation tube is fixed to the nut in such a manner that the outer surface of the ball circulation tube extending in parallel with the first direction is opposed to the outer surface of the nut.
Further, the above-mentioned object of a second aspect of the present invention would be invention, in a ball screw as set forth in the first aspect of the present invention, in a ball line formed by the large number of balls, there are inserted a plurality of spacers each having a modulus of longitudinal elasticity smaller than the modulus of longitudinal elasticity of each of the balls.
According to a third aspect of the invention, in a ball screw as set forth in the first or second aspect of the invention, the balls are respectively made of steel material and the spacers are respectively made of resin.
According to a fourth aspect of the invention, in a ball screw as set forth in the second or third aspect of the invention, the spacer is formed in a spherical shape almost identical in size with the ball.
According to a fifth aspect of the invention, in a ball screw as set forth in the second or third aspect of the invention, each of the spacers is formed in a disk-like shape having a diameter smaller than the diameter of each of the balls and also includes two concavely spherical surfaces respectively formed in the two end portions thereof that are opposed to the balls, while each of the concavely spherical surfaces has a radius of curvature larger than the radius of each of the balls.
According to a sixth aspect of the invention, in a ball screw as set forth in any one of the second to fifth aspects, the spacers are respectively interposed between the balls.
According to a seventh aspect of the invention, there is provided a ball screw, comprising: a screw shaft including a first spiral groove formed in the outer peripheral surface thereof; a nut disposed on the outer periphery of the screw shaft; a second spiral groove formed in the inner peripheral surface of the nut in such a manner that it is opposed to the first spiral groove: a large number of balls rollably held by and between the second spiral groove and first spiral groove; and, a ball circulation tube for forming a circulation passage for the balls in the outside of the nut, wherein, in a ball line formed by the large number of balls, there are inserted a plurality of spacers each having a modulus of longitudinal elasticity smaller than the modulus of longitudinal elasticity of each of the balls.
In a ball screw according to the first aspect of the invention, since the balls roll within the ball circulation tube in such a manner that they are arranged in a zigzag manner, variations in the torque of the ball screw caused by the mutual sliding movements of the balls occurring within the ball circulation tube can be restricted.
According to the second to seventh aspects of the invention, in case where the number of balls existing within the ball circulation tube increases and a so called ball packed phenomenon is thereby caused to occur within the ball circulation tube, the spacers are elastically deformed in the arrangement direction of the balls according to the ball packed amount (the varying amount of the number of balls existing within the ball circulation tube) and thus the ball packed amount can be absorbed by the spacers. This can restrict the variations in the torque of the ball screw which are caused by the ball packed phenomenon.
Also, according to the fourth aspect of the invention, since the balls are prevented from colliding with each other, there can be prevented generation of noises which would otherwise occur due to the mutual collision between the balls.
REFERENCES:
patent: 2890594 (1959-06-01), Galonska
patent: 3498153 (1970-03-01), Wagner
patent: 4074587 (1978-02-01), Brusasco
patent: 4304443 (1981-12-01), Hoffmann
patent: 4474073 (1984-10-01), Blaurock et al.
patent: 4750
Bucci David A.
Hansen Colby
NSK Ltd.
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