Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Reexamination Certificate
2002-12-12
2004-09-21
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
C428S192000, C384S520000, C384S551000, C492S015000
Reexamination Certificate
active
06794015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear motion device which causes a linear motion by the utilization of the rolling of rolling elements, such as steel balls or ceramic balls. More particularly, the invention relates to improvements of a structure of the retaining pieces interposed between the adjacent rolling elements and a linear motion device using the retaining pieces thus structured.
2. Description of the Related Art
Examples of the known linear motion device utilizing the rolling of a number of rolling elements are a linear motion guide bearing such as a linear guide or a linear ball bearing, and various types or screws having balls. Those linear motion devices are widely used as important mechanical components in many industrial machines.
As an example or this type of the device, a linear guide
10
is illustrated in plan, partly cut out, in FIG.
9
. As shown, the linear guide
10
generally includes a guide rail
1
, which axially extends, and a slider
2
, shaped like U in cross section, which straddles the guide rail. Ball rolling grooves
3
, while axially extending, are respectively formed in both side surfaces of the guide rail
1
. A ball rolling groove
5
, which faces a ball rolling groove
3
, is formed in the inner wall of each of both side portions of a slider body
2
A of a slider
2
. A number of steel balls B as rolling elements are put between those opposed ball rolling grooves
3
and
5
. The slider
2
is axially movable on and along the guide rail
1
, with the assistance of the rolling of the steel balls B. With the movement of the slider, the steel balls B, which are interposed between the guide rail
1
and the slider
2
, will move to the end of the slider body
2
A of the slider
2
. To continuously move the slider
2
in the axial direction, an endless circulation of those steel balls B is needed.
A linear through-hole
6
is axially formed in each side portion of the slider body
2
A. The linear through-hole serves as a ball return path. End caps
7
are applied to both ends of the slider body
2
A. Ball circulation tracks
8
, semicircular in cross section, are formed in the caps so as to interconnect a path defined by the ball rolling grooves
3
and
5
and the linear through-hole
6
, whereby a ball endless circulation track
9
is formed.
A ball screws mechanism
20
is perspectively illustrated, partly cut out, in FIG.
10
. As shown, a ball nut
12
is fit to an axially extending threaded shaft
11
. A thread groove
11
a
, semicircular in cross section, is formed in the outer peripheral surface or the threaded shaft
11
. A thread groove
12
a
, semicircular in cross section, is formed in the inner peripheral surface of the ball nut
12
. The thread groove
11
a
of the threaded shaft
11
is confronted with the semicircular thread groove
12
a
of the ball nut
12
. A number of steel balls B as rolling elements are put in a path defined by those thread grooves
11
a
and
12
a
. The threaded shaft
11
and the ball nut
12
are relatively moved in the axial direction with the assistance of the rolling of the steel balls (for example, the threaded shaft
11
is axially rotated while the ball nut
12
rectilinearly moves.). With the relative movement, the steel balls B move while rolling in and along the spiral track defined by the thread grooves
11
a
and
12
a
. To continuously move the ball nut
12
, an endless circulation of those steel balls B is needed.
A couple of circulation holes
17
are formed in the thickness of the ball nut
12
in a state that it straddles the threaded shaft
11
and is opened to the outside of the nut. The circulation holes
17
communicatively connect to the spiral track while extending in the tangential direction with respect to the path. A ball circulating track
18
is formed by coupling the circulation holes
17
by means of a ball tube
14
A shaped like U (two ball circulating tracks
18
are used in the illustrated instance). After the steel balls B move a distance of, for example, 1.5 turn within the spiral track, those are introduced into the ball circulating track
18
and move in an endless circulating manner.
Smoother and more stable operations of the steel balls B as rolling elements, low noise and the like are required for the linear motion device. To meet the requirements, a measurement has been employed in which a spacer ball of the reduced diameter is interposed between the adjacent load balls. Where the measure is employed, the following problem arises anew, however. As the result of the interposing of the spacer ball, a span between the load balls is elongated. As an inevitable consequence, the load capacity and rigidity of the linear motion device are reduced. Therefore, a following approach is experimentally made. Retaining pieces (also called separators)
30
are each interposed between the adjacent steel balls B as shown in FIG.
11
. By the retaining pieces
30
thus arranged, gaps in the row of the steel balls in their moving direction are eliminated and compression force is forcibly plied to the steel balls B, whereby the operability and the noise characteristic are improved.
To further improve the operability and noise characteristic, various proposals have been made which are constructed giving attention to the shape of the retaining piece
30
and the gaps present between the adjacent steel balls B and the retaining pieces
30
.
The applicant of the present patent application proposed the following retaining piece structures in Japanese Patent Unexamined Publication No. 2000-120825:
1) In the retaining piece structure, a retaining piece has two recessed surfaces respectively facing to the balls. Each recessed surface is shaped such that it contacts with the steel ball at its outer edge or near outer edge. With this novel and unique technical feature, the low noise generation is achieved, and the operability is improved by maximizing the overlapping width of the retaining piece over which it contacts with the steel ball. Further, the spans between the steel balls are controlled at high precision.
2) In another structure, a retaining piece has recessed surfaces so shaped as to be in liner contact with the balls. This retaining piece structure also achieves the low noise generation. Further, the operability is improved since sliding resistance between the retaining pieces and the balls is small, and stable ball holding by the retaining pieces is secured.
The applicant of the present patent application proposed novel and unique retaining piece structure in Japanese Patent Unexamined Publication No. 2000-213538. In the retaining piece structure, proper gaps are provided in one ball row containing retaining pieces and balls, whereby the low noise generation and the improvement of the operability are achieved (those effects are high in level when the gap dimension is selected to be within 2% to 63% of the ball diameter.).
The retaining piece structure of Japanese Patent Unexamined Publication No. 2000-120825 is capable of satisfying the proper gap dimension described in Japanese Patent Unexamined Publication No. 2000-213538 if it is used in normal condition and the gap dimension is within a proper range of dimension values. Under a large pre-load and a large moment load, a load acting on the retaining piece (a pressing force of the ball against the recessed surface of the retaining piece) is large. As a result, the retaining piece is deformed, the ball-to-ball span is reduced, and the ball row will possibly lose its proper gap dimension.
When the linear motion device is used for a long time under hard conditions, the recessed surfaces of the retaining pieces will be worn and/or yielded. In this case, the ball-to-ball span is considerably reduced, the proper gap dimension is lost, and the revolution of the ball is abnormal. This problem remains unsolved.
An explanatory figure of the above structures is FIG.
8
. In this figure, by the retaining pieces
30
A arranged, gaps in the row of the steel balls in their moving direction
Kasuga Shinichi
Sato Ryoichi
Yamaguchi Hiroki
Loney Donald J.
NSK Ltd.
Sughrue & Mion, PLLC
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