Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
2002-02-05
2004-04-20
Joyce, William C. (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S424860
Reexamination Certificate
active
06722223
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a ball screw. More particularly, the invention relates to a ball screw which is little subject to deterioration of operating characteristics and occurrence of wear, torque change, noise, vibration, etc. due to stagnation or competition of balls.
A ball screw comprises a screw shaft and a nut. An outer surface of the screw shaft and an inner surface of the nut are provided with the respective helical thread grooves corresponding to and confronting with each other. The helical space formed between the two thread grooves, i.e., ball rolling path is filled with a number of balls while allowing the balls to rotate. In this arrangement, the screw shaft and the nut make a relative helical movement with the rolling of these balls to make a relative movement in the axial direction.
Such a ball screw has a gap formed between the adjacent balls. As the balls roll, the total of all the gaps in one circuit varies with every movement of one ball.
In particular, a ball screw for use in injection molding machine or the like, i.e., ball screw comprising balls having a diameter relatively greater than the diameter of the shaft and hence having a relatively great scooping angle tends to have a great variation of the total of gaps (value obtained by totaling the gaps between the balls over the entire ball screw).
Thus, a ball screw which varies greatly in the total of gaps between balls is subject to deterioration of operating characteristics and occurrence of wear, torque change, noise (noise of ball slipping), vibration, etc. during the rolling of balls (during the operation of ball screw) due to stagnation or competition of balls to disadvantage.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a ball screw which is little subject to deterioration of operating characteristics and occurrence of wear, torque change, noise, vibration, etc. during operation due to stagnation or competition of balls.
The foregoing object of the invention will become apparent from the following detailed description and examples.
The foregoing object of the invention can be accomplished with the following constitution. A ball screw, according to the present invention, comprises a screw shaft, a nut and a number of balls. The screw shaft has a helical thread groove formed on the outer surface thereof. The nut has a thread groove formed on the inner surface thereof corresponding to the thread groove on the screw shaft which engages with the screw shaft with the interposition of the balls rollably provided in a helical ball rolling path formed between the two thread grooves. In the ball screw, the variation of the total of the gaps between the balls during the rolling of the balls is smaller than {fraction (1/20)} of the diameter of the ball.
In this arrangement, the ball screw is little subject to deterioration of operating characteristics and occurrence of wear, torque change, noise, vibration, etc. during operation due to stagnation or competition of balls. The ball screw is also little subject to wear or damage on the constituent members such as ball.
The invention can be applied also to a ball screw comprising a spacer for retaining a ball provided interposed between balls. In this case, the variation of the total of the gap between the spacers and the balls during the rolling of the balls is predetermined to be smaller than {fraction (1/20)} of the diameter of the ball.
Such a ball screw can exert an effect of preventing the spacer from falling down in the ball rolling path or an effect of preventing the spacer from being damaged besides the foregoing effect.
REFERENCES:
patent: 2473743 (1949-06-01), Barnes
patent: 2505131 (1950-04-01), Means, Jr.
patent: 2674899 (1954-04-01), Gobereau
patent: 2694942 (1954-11-01), Hellen
patent: 3053105 (1962-09-01), Cole
patent: 3791232 (1974-02-01), Helmer
patent: 4274297 (1981-06-01), Blurock et al.
patent: 6149307 (2000-11-01), Kamimura et al.
Kanda Toru
Maruyama Daisuke
Sannomiya Hitoshi
Joyce William C.
NSK Ltd.
Sughrue & Mion, PLLC
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