Automatic ball balancer for rotating machine

• US 6,132,354 A
• Filed: 11/07/1997
• Issued: 10/17/2000
• Est. Priority Date: 11/08/1996
• Status: Expired due to Term

• Current Assignee: Hitachi KOKI Company Limited (Koki Holdings Co., Ltd.)
• Original Assignee: Hitachi KOKI Company Limited (Koki Holdings Co., Ltd.)
• Inventors: Ohtsu, Shinki, Yoshioka, Masanori, Ishikawa, Mitsuyuki
• Primary Examiner(s): Cooley, Charles E.
• Application Number:
  US08/965,768
• Time in Patent Office: 1,075 Days
• Field of Search: 494/16, 494/20, 494/82, 210/144, 210/363, 74/572, 74/573 R, 74/574, 422/72, 68/23.1-23.3
• US Class Current: 494/16
• CPC Class Codes: B04B 9/14 Balancing rotary bowls balancing per se G01M; Schrappers
• CPC Class Codes: F16F 15/363 using rolling bodies, e.g. balls free to move in a circumferential direction
• CPC Class Codes: Y10T 74/2109 Balancing for drum, e.g., washing machine or arm-type structure, etc., centrifuge, etc.

Abstract

A ball balancer for minimizing a dynamic unbalance of a moving part of a rotating machine such as a centrifuge is provided. The ball balancer includes a rotary balancer casing having disposed therein balls. The rotary balancer casing is mounted on the moving part coaxially with an axis of rotation thereof and has formed therein an inner side wall which is so curved that the balls are lifted away from the bottom of the balancer casing along the inner side wall by the centrifugal force and biased toward the opposite side of an unbalanced mass of the moving part when the rotational speed of the moving part exceeds a resonant speed that is a rotational speed of the moving part when matched with a natural frequency of the moving part, thereby counterbalancing the unbalanced mass of the moving part. In an alternative form, the balls include a first group having a large diameter and a second group having a small diameter. The large-diameter balls and the small-diameter balls are arranged alternately. Each of the large-diameter balls is lifted on adjacent one of the small-diameter balls by the reaction force produced by a shift in center between one of the large-diameter balls and adjacent one of the small-diameter balls arranged on the bottom of the balancer casing and biased toward the opposite side of the unbalanced mass of the moving part when the rotational speed of the moving part exceeds the resonant speed.

Claims

1. A ball balancer for controlling a dynamic balance of a moving part of a rotating machine comprising:

a rotary balancer casing mounted on an axis of rotation coaxial with an axis of rotation of the moving part of the rotating machine, said rotary balancer casing including a cylindrical inner side wall and a bottom and having an annular race formed on the bottom along a periphery of the cylindrical inner side wall;

balls disposed on the annular race of said rotary balancer casing over a first angular range; and

means for holding said balls arranged on the annular race over the first angular range within a lower-speed range of rotation of the moving part of the rotating machine less than or equal to a resonant speed that is a rotational speed of the moving part when matched with a natural frequency of a rotating system including the ball balancer and the moving part and that induces oscillation of the rotating system to increase, when the rotational speed of the moving part is increased out of the lower-speed range, said means biasing said balls to the opposite side of an unbalanced mass of the moving part, which initiates oscillation of the moving part, within a second angular range smaller than the first angular range, wherein the cylindrical inner side wall includes an upper portion and a lower portion which constitute said means, the lower portion being so curved outward of said rotary balancer casing at a given radius of curvature that an interval between the axis of rotation of said rotary balancer casing and an inner surface of the lower portion in a direction perpendicular to the axis of rotation of said rotary balancer casing is increased toward the upper portion and that an angle between a tangent passing through a point on the inner surface of the lower portion with which each of said balls is in contact and a vertical line allows said balls to be lifted away from the annular race along the inner surface of the lower portion by centrifugal force produced when the rotational speed of the moving part of the rotating machine exceeds the resonant speed.

2. A ball balancer as set forth in claim 1, wherein the upper portion of the cylindrical inner side wall is curved at the same radius of curvature as that of the lower portion and an interval between the axis of rotation of said rotary balancer casing and an inner surface of the upper portion in a direction perpendicular to the axis of rotation of said rotary balancer casing is decreased as leaving the lower portion.

3. A ball balancer as set forth in claim 1, wherein said upper portion of the cylindrical inner side wall is curved at a radius of curvature greater than that of the lower portion.

4. A ball balancer as set forth in claim 1, wherein said upper portion of the cylindrical inner side wall has a flat inner surface extending parallel to the axis of rotation of said rotary balancer casing.

5. A ball balancer as set forth in claim 1, wherein said balls includes a first group of large-diameter balls and a second group of small-diameter balls.

6. A ball balancer as set forth in claim 5, wherein the large-diameter balls and the small-diameter balls are arranged in alternate fashion.

7. A ball balancer for controlling a dynamic balance of a moving part of a rotating machine comprising:

a rotary balancer casing mounted on an axis of rotation coaxial with an axis of rotation of the moving part of the rotating machine, said rotary balancer casing including a cylindrical inner side wall and a bottom and having an annular race formed on the bottom along a periphery of the cylindrical inner side wall;

balls disposed on the annular race of said rotary balancer casing over a first angular range; and

means for holding said balls arranged on the annular race over the first angular range within a lower-speed range of rotation of the moving part of the rotating machine less than or equal to a resonant speed that is a rotational speed of the moving part when matched with a natural frequency of a rotating system including the ball balancer and the moving part and that induces oscillation of the rotating system to increase, when the rotational speed of the moving part is increased out of the lower-speed range, said means biasing said balls to the opposite side of an unbalanced mass of the moving part, which initiates oscillation of the moving part, within a second angular range smaller than the first angular range, wherein said balls includes a first group of large-diameter balls and a second group of small-diameter balls, a difference in diameter between the large-diameter balls and the small-diameter balls constituting said means.

8. A ball balancer as set forth in claim 7, wherein the large-diameter balls and the small-diameter balls are arranged in alternate fashion.

9. A ball balancer as set forth in claim 7, wherein the cylindrical inner side wall of said rotary balancer casing extends vertically in parallel to the axis of rotation of said rotary balancer casing, and wherein an inner diameter of the cylindrical inner side wall and the difference in diameter between the large-diameter balls and the small-diameter balls are so determined that the large-diameter balls are lifted away from the annular race by centrifugal force acting on the large-diameter balls and the small-diameter balls when the rotational speed of the moving part is increased out of the lower-speed range.

10. A centrifuge comprising:

(a) a rotating member; and

(b) a ball balancer for controlling a dynamic balance of the rotating member, said ball balancer including,

(1) a rotary balancer casing mounted on an axis of rotation coaxial with an axis of rotation of said rotating member, said rotary balancer casing including a cylindrical inner side wall and a bottom and having an annular race formed on the bottom along a periphery of the cylindrical inner side wall;

(2) balls disposed on the annular race of said rotary balancer casing over a first angular range; and

(3) means for holding said balls arranged on the annular race over the first angular range within a lower-speed range of rotation of said rotating member less than or equal to a resonant speed that is a rotational speed of said rotating member when matched with a natural frequency of a rotating system including the ball balancer and said rotating member and that induces oscillation of the rotating system to increase, when the rotational speed of said rotating member is increased out of the lower-speed range, said means biasing said balls to the opposite side of an unbalanced mass of said rotating member, which initiates oscillation of said rotating member, within a second angular range smaller than the first angular range, wherein said rotating member includes a rotor rotatably supported by a shaft, said rotor including a rotor body and a cover, the rotor body having formed therein a plurality of chambers with openings for taking mixtures to be separated in and out, the cover being disposed on the rotor body to close the openings, further comprising a motor revolving said rotor through the shaft, and wherein said ball balancer is mounted in the cover of said rotor.