Ball-threaded shaft anti-slipout type linear actuator

• US 5,910,692 A
• Filed: 12/04/1997
• Issued: 06/08/1999
• Est. Priority Date: 12/06/1996
• Status: Expired due to Fees

• Current Assignee: Tsubakimoto Co.
• Original Assignee: Tsubakimoto Chain Company
• Inventors: Nakamura, Kenichiro, Komada, Minoru, Saeda, Koichi, Mitsuyama, Toshio
• Primary Examiner(s): Ramirez, Nestor
• Assistant Examiner(s): JONES, JUDSON
• Application Number:
  US08/985,046
• Time in Patent Office: 551 Days
• Field of Search: 310/12, 310/13, 310/14, 310/23, 310/89, 361/23, 361/51, 74/89.15, 74/425, 74/606 R, 74/424.7, 74/424.8 R, 318/135, 318/261, 318/282, 318/434, 318/469, 318/475, 318/476, 307/119
• US Class Current: 310/13
• CPC Class Codes: F16H 2025/2081 Parallel arrangement of drive motor to screw axis
• CPC Class Codes: F16H 2025/2093 using conical gears
• CPC Class Codes: F16H 25/20 Screw mechanisms with automatic reversal F16H25/12
• CPC Class Codes: F16H 25/2204 with balls
• CPC Class Codes: F16H 25/2454 Brakes; Rotational locks
• CPC Class Codes: Y10T 74/19702 Screw and nut

Abstract

To prevent a ball-threaded shaft from slipping out of a linear actuator, a linear actuator 10 has an output shaft 18 threaded in a nut 16 for moving forward and backward linearly with respect to an outer tube 22 secured to a housing 20. Linear reciprocating movement of the nut 16 is effected by a ball-threaded shaft 14 rotated normally and reversely by a driving motor 12. The shaft is held against axial displacement by a bearing assembly 8 having an axial disk 32 secured to a proximal end 24 of the ball-threaded shaft 14. On the nut side of the disk within the assembly are disposed a first tension receiving rotational body 36, a thrust bearing 45 and a second tension receiving rotational body 58. The assembly 8 is retained by a tension stopper 62 spread and inserted into an annular central groove 60 in the tube 22. The second tension receiving rotational body 58 is formed with a reduced diameter preventing circumferential surface 66 corresponding to an inner peripheral circumferential surface of the C-shaped tension stopper 62. Even if tension and a rotating force are exerted on the tension stopper 62, causing it to be reduced in diameter, the inner peripheral surface thereof comes into contact with the reduced diameter preventing surface 66.

Claims

1. A linear actuator having a housing and an output shaft mounting a nut, a ball-threaded shaft adapted for moving said nut forward and backward with respect to the housing by linear reciprocating movement of the nut on said ball-threaded shaft, and a driving motor normally and reversely rotating said ball-threaded shaft, said actuator comprising:

an axial disk fixedly mounted on a proximal end of said ball threaded shaft;

a first tension receiving rotational body loosely fitted in said housing at said proximal end adjacent to the nut between said axial disk and said nut;

thrust bearing components interposed between the opposed surfaces of said axial disk and said first tension receiving rotational body;

a coil spring frictionally engaging the outer periphery of said axial disk and said first tension receiving rotational body;

an internal annular groove in said housing surrounding said ball-threaded shaft between said first tension receiving body and said nut;

a C-shaped tension stopper spread and inserted into said internal annular groove of said housing and having a rectangular cross section, said cross section having a tension-receiving surface preventing axial displacement of said first body in a direction of tension exerted on said ball threaded shaft and an inner peripheral circumferential surface; and

a second tension receiving rotational body disposed between said first tension receiving rotational body and said tension stopper to transmit tension to said tension stopper from said axial disk, said thrust bearing components and said first tension receiving rotational body, characterized in that

said second tension receiving rotational body is formed with a reduced diameter preventing shoulder forming an annular recess with a tension exerting axial surface confronting said tension receiving surface of said tension stopper and a tension stopper reduced diameter preventing circumferential surface opposed to said inner peripheral circumferential surface of said tension stopper with a slight clearance.

2. The linear actuator according to claim 1 wherein said first tension receiving rotational body and said second tension receiving rotational body are integrated.

3. The linear actuator according to claim 1 including a resin washer positioned between said first tension-receiving body and said second tension-receiving body.

4. A linear actuator having a housing, a driving motor, an output shaft, a nut carried by said output shaft and adapted to be linearly moved forward and backward with respect to the housing, a ball-threaded shaft engaging said nut, normally and reversely rotated by said driving motor, comprising:

an axial disk fixedly mounted on a proximal end of said ball threaded shaft;

a first tension receiving rotational body loosely fitted in said housing at said proximal end adjacent to the nut between said axial disk and said nut;

first thrust bearing components interposed between the opposed surfaces of said axial disk and said first tension receiving rotational body;

a coil spring frictionally engaging the outer periphery of said axial disk, said first tension receiving rotational body;

an internal annular groove in said housing surrounding said ball-threaded shaft between said first tension receiving body and said nut;

a C-shaped tension stopper spread and inserted into said annular groove and having a rectangular cross section, said cross section having a tension-receiving surface preventing axial displacement of said first body in a direction of tension exerted on said ball threaded shaft and an inner peripheral circumferential surface;

a pressing force receiving body loosely fitted in said housing between the axial disk and the extreme end of the proximal end and having an outer periphery frictionally engaged with said coil spring;

second thrust bearing components interposed between the opposed surfaces of said axial disk and said pressing force receiving body;

a pressing force stopper secured to said housing on the extreme end side of the proximal end of said pressing force receiving rotational body and preventing axial displacement of said body in the direction of pressing force exerting on said ball-threaded shaft; and

a second tension receiving rotational body disposed between said first tension receiving rotational body and said tension stopper to transmit tension to said tension stopper from said axial disk, said first thrust bearing components and said first tension receiving rotational body, characterized in that

said second tension receiving rotational body is formed with a reduced diameter preventing shoulder forming an annular recess with a tension exerting axial surface confronting said tension receiving surface of said tension stopper and a tension stopper reduced diameter preventing circumferential surface opposed to said inner peripheral surface of said tension stopper with a slight clearance.

5. The linear actuator according to claim 4, wherein said first tension receiving rotational body and said second tension receiving rotational body are integrated.

6. The linear actuator according to claim 4 including a resin washer positioned between said first tension-receiving body and said second tension-receiving body.

7. A linear actuator having an elongated housing with an inner periphery having an annular groove centrally therein;

a ball threaded shaft mounted for rotation within said inner periphery and adapted to be normally and reversely rotated by a driving motor;

a bearing assembly mounting said ball-threaded shaft against axial displacement in said elongated housing;

a C-shaped tension stopper spread and inserted into said annular groove and having a rectangular cross section, said cross section providing an axial surface projecting inwardly from said groove into said elongated housing and a circumferential surface on its inner periphery;

a pressing force stopper in said housing spaced from said tension stopper, said bearing assembly being mounted between said stoppers;

an output shaft coaxial with said ball-threaded shaft in said housing and having a nut threadedly engaging said ball-threaded shaft and operable to be linearly moved forward and backward with respect to said housing by said normal and reverse rotation of the ball-threaded shaft, said output shaft being subject to tension tending to move said output shaft forwardly and a pressing force tending to move said output shaft rearwardly;

said bearing assembly comprising;

an axial disk fixedly mounted on a proximal end of said ball threaded shaft with one axial surface facing forwardly toward said nut and opposite axial surface facing backwardly;

at least one rotational body loosely fitted on said proximal end and having an axial surface confronting one of said axial surfaces of the disk,

thrust bearing components interposed between the confronting surfaces of said axial disk and said at least one rotational body,

a coil spring frictionally engaging the outer peripheries of said axial disk and said at least one rotational body,

said bearing assembly having an end positioned to transmit tension to said C-shaped tension stopper from said axial disk,

said bearing assembly end having a shoulder comprising a tension-exerting axial surface opposed to said inwardly projecting axial surface of said tension stopper and a circumferential surface opposed to the inner peripheral circumferential surface of said tension stopper with a slight clearance, whereby upon application of tension to said output shaft, the axial surface of said shoulder engages the axial surface of said stopper and limits axial displacement of said bearing assembly, and the circumferential surface of said shoulder engages the circumferential surface of said stopper to preclude disengagement of said stopper from said annular groove.

8. A linear actuator according to claim 7, wherein said at least one rotational body comprises:

a first tension receiving rotational body loosely fitted on said proximal end adjacent to said one axial surface of said axial disk, said bearing assembly including

a second tension receiving rotational body disposed between said first tension receiving rotational body and said tension stopper to transmit tension to said tension stopper from said axial disk,

said shoulder being formed on said second tension receiving rotational body.

9. The linear actuator according to claim 8 wherein said first tension receiving rotational body and said second tension receiving rotational body are integrated.

10. The linear actuator according to claim 8 including a washer positioned between said first tension-receiving rotation and said second tension-receiving rotational body.

11. The linear actuator according to claim 7 wherein said axial surface of the C-shaped tension stopper has a given radial depth greater than the groove radial depth whereby the difference between said radial depth provides said inwardly projecting axial surface of said tension stopper,

said slight clearance between said circumferential surfaces being less than the groove radial depth.

12. The linear actuator according to claim 11 wherein the width of the groove along the axis of the housing snugly receives the thickness of said stopper, the width of the circumferential surface of the shoulder being preferably greater than the thickness of the stopper so as to reduce the likelihood of the stopper slipping past the shoulder as it is reduced in diameter by the combined tension and rotational force.