Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
2002-05-14
2004-08-24
Fenstermacher, David (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C384S051000
Reexamination Certificate
active
06779419
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a linear motion device used in, for example, the machine tool. More particularly, the present invention relates to a linear motion guide bearing device in which retainer pieces are each interposed between adjacent rolling elements which circulatingly roll in the longitudinal direction of a guide rail. In addition, the present invention relates to a ball screw device in which retainer pieces are each interposed between adjacent rolling elements which circulatingly roll along an element rolling groove, spirally shaped, defined by a thread groove of a ball screw shaft and a thread groove of a nut.
The present invention relates to retainer pieces each disposed between adjacent balls in order to secure good operation of a ball screw. In this specification, the term “the thickness of the retainer piece” or the “thickness” on the retainer piece does not means the thickness of the whole retainer piece, but means the thickness of the retainer piece to separate the surface of a ball from the surface of another ball adjacent to the former. To be more precise, the “thickness” on the retainer piece means that the thickness of the retainer piece at a position with respect to a position defined a line connected centers of adjacent rolling elements, when two rolling elements are arranged on a collinear.
A linear motion guide bearing device
10
as shown in
FIG. 9
is known for a device for linearly guiding a work table of, for example, a machine tool. The linear motion guide bearing device
10
is provided with a guide rail
11
being rectangular in cross section. Rolling grooves
12
for the rolling elements are formed on both side surfaces of the guide rail
11
, and from one end to the other end of the guide rail
11
. A plurality of spherical rolling elements
13
(see
FIG. 10
) are engaged with each other in the rolling grooves
12
. When the rolling elements
13
roll along the rolling element grooves
12
, a slider
14
is relatively moved in the longitudinal direction of the guide rail
11
.
In the slider
14
have a slider body
15
straddling the guide rail
11
, and end caps
16
provided at the front end and the rear end of the slider body
15
. Rolling grooves
17
for the rolling elements (see
FIG. 10
) are arcuate in cross section and are formed in the inner side walls of the each of sleeves
15
a
of the slider body
15
of the slider
14
, respectively. The spherical rolling elements
13
roll in and along a rolling-element passage which is formed between the rolling grooves
17
and the rolling grooves
12
.
A passage hole for the rolling elements
18
is provided within each of the sleeves
15
a
of the slider body
15
and extends parallel to the rolling grooves
17
. The rolling grooves
17
and the passage holes
18
form an endless circulating raceway
20
of the rolling elements
13
together with rolling-element return passages
19
formed in the end caps
16
.
In the linear motion guide bearing device, when the rolling elements forcibly rub with each other with the movement of the slider
14
, early wear of the rolling elements and generating noise are frequently caused. To avoid this, retainer pieces
21
are each interposed between adjacent rolling elements
13
, thereby preventing the rolling elements from coming in contact with one another. In the linear motion guide bearing device, as shown in
FIG. 11
, the pitches among the rolling elements of a rolling element series
22
which is constructed with spherical rolling elements
13
and the retainer pieces
21
are equal in dimension. Accordingly, the periodical passing vibration of the rolling elements occurs at a fixed period with the movement of the slider
14
. The periodical passing vibration vibrates the bearing. This makes it difficult to further enhance the noise characteristic and motion accuracy. The same thing is correspondingly applied to the screw device in which the retainer pieces are each interposed between adjacent rolling elements.
In Japanese patent application No. Hei. 9-100839 (U.S. Pat. No. 5,927,858 (Jul. 27, 1999), a linear motion guide bearing device in which thereby eliminating the presence of indentations on the raceway surface on which the rolling elements
13
roll, or reducing the vibrations and noises, which are due to the fact that the rolling elements
13
on the element endless circulating raceways simultaneously enter the load path is described.
In the linear motion guide bearing device disclosed, the retainer pieces, which are each interposed between adjacent rolling elements in the rolling element series, are all different in their pieces having different thicknesses must be prepared. This brings about cost increase in the manufacturing of the retainer pieces and assembling of them into between the adjacent rolling elements.
In a ball screw device, balls(rolling elements) are arranged in the ball screw to support a load. Those balls roll in a circulating manner, and through the ball rolling, a good rotation-to-linear motion conversion is secured while maintaining load capacity and rigidity. Since the rolling of the balls occurs randomly, sometimes adjacent balls act to mutually impart compression forces to each other, and the slipping state often occurs. As a result, the balls exhibit great resistance to impede the rolling of other balls, so that a torque variation occurs and causes operation trouble.
A ball screw is known which, to solve such a problem, retainer pieces are each disposed between adjacent balls, and resistance acting to impede the rolling of other balls is not generated by avoiding the mutual ball contact.
In the ball screw, the balls are arranged at substantially regular spatial intervals by use of the retainer pieces, and the following new problems arise.
1) As shown in
FIG. 12
, when the surface
62
of the shaft on which balls
61
are disposed or the groove surface of the nut, which surface is brought into contact with the balls
61
, is ground, very fine process-waving
63
caused by the oscillation of a grinding wheel inevitably takes place on the contacting surface. This is a phenomenon always occurring in machining objects as well as in the ball screw. This fact implies that even if an object is highly precisely machined and the precision of the machined object is visually (macroscopically) high, the very fine process-waving occurs when microscopically observed. In this state, retainer pieces
64
having thicknesses being uniform in value are disposed in the ball screw. As a result, there is a case that a distance
66
between adjacent balls of those regularly arranged balls is coincident or substantially coincident in length with the pitch of the process-waving. If those are coincident, the number of contact positions
68
where the balls come in contact with top parts of the fine process-waving is equal to the number of the balls as the greatest number. Also when the distance is coincident with the bottom parts of the fine process-waving, the number of contact positions is equal to the number of the balls as the greatest number. The influence by the variation of friction acts by the number of balls. This possibly leads to operation impairment due to the friction variation, and abnormal sound generation and noise increase, which result from the coincidence of the balls
61
with the process-waving
63
.
2) Where in the ball screw utilizing the retainer pieces
64
, one kind of retainer pieces is used and the machining accuracy is not different, to avoid the problem 1) above arising from the coincidence of the ball(element)-to-ball(element) distance between the balls with the pitch of the process-waving
63
, consideration at design or machining stage is needed, so that the pitch of the very fine process-waving
63
is not coincident with the ball-to-ball distance. In other words, consideration on a microscopic condition of the surface produced by the machining is an essential matter in design and machining. This is very difficult and needs complicated work.
3) Also in controlling, in de
Fenstermacher David
NSK Ltd.
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