Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
2001-02-27
2002-11-19
Joyce, William C (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S424810, C074S424840
Reexamination Certificate
active
06481305
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a roller screw which comprises a screw shaft, a nut member,and a plurality of rollers interposed between the screw shaft and nut member.
2. Description of the elated Art
Conventionally, the e is known a ball screw in which a plurality of balls are interposed between a screw shaft and a nut member. Now,
FIG. 5
shows an axial-direction section of a ball screw of this type. In case where a screw shaft
1
is rotated with respect to a nut member
2
, the number member
2
is allowed to reciprocate in the axial direction of the screw shaft
1
. Balls
3
are all wed to roll between the screw shaft
1
and nut member
2
along the outer periphery of the screw shaft
1
. By the way, the ball screw, in some cases, can be given an axial-direction load (
1
) or an axial-direction load (
2
) as an external load. The axial-direction load (
1
) is an external load which occurs when the nut member
2
moves forward, whereas the axial-direction load (
2
) is an external load which occurs when the number
2
moves backward. These two axial-direction loads (
1
) and (
2
) are directed in the mutually opposite directions. As shown in
FIG. 5
, the right and left half sections of each ball
3
are symmetric in the axial-direction section thereof and, therefore, either of the left and right surface
3
a
or
3
b
of the ball
2
is able t receive the load. That is, the ball screw is able to receive both of the axial-direction load (
1
) and (
2
) which occur in he reciprocating motion thereof.
In some of the ball crews, there can be a case where there is a great difference in size between the two axial-direction loads (
1
) and (
2
). For example, in case where the ball screw is used in an injection molding machine, when fluidized resin is pushed into a metal mod using a push-in device, dozens of tons of axial-direction load is applied to the ball screw, whereas, when the push-in device itself is moved back, only a slight axial-direction load is a plied to the ball screw.
Conventionally, as a all screw suitable for the case where the above-mentioned axial-direction loads occurring in the forward and backward are different in size, as shown in
FIG. 5
, there is known a ball crew (see JP-A-11-257455) in which not only a portion of a
5
spiral-shaped load rolling groove
2
a
formed in the nut member
2
is shifted with respect to a spiral-shaped load rolling groove la formed in the screw shaft
1
but also the number of effective windings of the load rolling groove
2
a
for receiving a high load is set larger than the number of effective windings of the load rolling groove
2
a
for receiving a low load. According to this ball screw, a contact angle line
4
, which is obtained by connecting together two contact points, that is, a contact point between the ball
3
and the ball rolling groove
1
a
formed in the screw shaft
1
and a contact point between the ball
3
and the ball rolling groove
2
a
formed in the nut member
2
, can be incline to thereby receive the two different forward and backward axial-direction loads (
1
) and (
2
) applied to the ball screw during the reciprocating motion thereof.
Also, in case of a roller screw in which rollers are interposed between a nut member and as screw shaft, the nut member reciprocates with respect to the screw haft in the axial direction thereof; and, therefore, the roll r screw is requested to be able to receive not only an axial-direction load occurring in the forward motion thereof but also a axial-direction load occurring in the backward motion thereof. However, each of the rollers, unlike the ball, is not formed symmetric (that is, it is not spherical in shape). There ore, in the case of the roller screw, unlike the ball screw, the direction of the axial-direction load that can be received by the roller screw is limited to one direction; and thus, the roller screw is not be able to receive both of the axial direction loads that respectively occur in the forward and backward motion of the roller screw. Even in case where, as di closed in JP-A-257455, a portion of a load rolling groove formed in the nut member is shifted with respect to a roller rolling groove formed in the screw shaft, the roller screw can not receive both of the axial-direction loads respectively occurring in the forward and backward motion of the roller screw.
As a roller screw which is structured such that it is able to receive both of the axial-direction loads respectively occurring in the forward and backward motion thereof, there is known a roller screw which is disclosed in JP-A-210858.
FIG. 6
shows an axial-direction section view of this roller screw, and
FIG. 7
shows rollers which are arranged and stored in a roller rolling groove formed in the roller screw shown in FIG.
6
. As shown in
FIGS. 6 and 7
, between a V-shaped load rolling groove formed in a nut member
5
and a V-shaped load rolling groove formed in a crew shaft
6
, there are cross arranged rollers
7
; that is, the mutually adjoining rollers
7
cross each other. More specifically, the roller
7
, which rolls between the wall surface
5
a
of the load rolling groove and the wall surface
6
a of the load rolling groove, and the roller
7
, which rolls between the wall surface
6
a
of the load rolling groove and the wall surface
6
b
of he load rolling groove, are arranged alternately.
However, in the roller crew of this type, since the mutually adjoining rollers
7
cross each other, when the axial-direction load (
1
) or the axial-direction load (
2
) is applied to the roller screw, the rolling roller and the roller
7
, which does not roll but slides, are arranged alternately. In this alternate arrangement of rollers, there is a fear that the rolling motion of the rollers
7
or the pick-up operation of the rollers
7
can be interfered. Also, to be able to pick up the mutually crossing rollers
7
with a single return pipe, the section shape of a no-load return passage within the return pipe and the side surface shapes of the rollers must be square, which limits the shape of the return pipe or the shapes of the rollers that can be used. Further, since the number of rollers
7
for receiving the axial-direction load (
1
) occurring in the forward motion of the roller screw is set equal to that of rollers
7
for receiving the axial-direction load (
2
) occurring in the backward motion, when the axial-direction load (
1
) in the forward motion and the axial-direction load (
2
) in the backward motion are different in size, a roller screw must be selected according to the higher one of the two loads, which makes it inevitable that the whole length of the nut member is long.
SUMMARY OF THE INVENTION
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional roller screws. Accordingly, it is an object of the invention to provide a roller screw and a method for arranging rollers in a roller screw, which not only can receive both of the forward- and backward-motion axial direction external loads but also can prevent the circulatory motion of rollers from being interfered.
Incidentally, in the following description, for the purpose of easy understanding of the invention, the reference numerals of the accompanying drawings are given in parentheses. However, it should be noted here that the invention is not limited to embodiments illustrated herein.
In attaining the above object, according to a first aspect of the invention, a plurality of rollers to be interposed between a nut member and a screw shaft are composed of a forward-motion load roller group the rollers of which are arranged in such a manner that the center lines thereof are set at a given angle with respect to the center line of the screw shaft, and a backward-motion load roller group the rollers of which are arranged in such a manner that the center lines thereof are set at an angle, which is different from the above-mentioned given angle, with respect of the center line of the screw shaft; and, the forward-motion l
Kimura Shino
Nishimura Kentarow
Joyce William C
Morgan & Lewis & Bockius, LLP
THK Co. Ltd.
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