Universal coupler for a self aligning linear actuator

Details Universal coupler for a self aligning linear actuator Universal coupler for a self aligning linear actuator

2000-04-25

2001-08-07

Rivell, John (Department: 3753)

Valves and valve actuation

Electrically actuated valve

Rotary electric actuator

C251S086000, C074S424830

Reexamination Certificate

active

06270054

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to lifting screw mechanisms and, more particularly, the invention relates to throttle valve control assemblies for semiconductor wafer processing chambers.
2. Description of the Background Art
Throttle valves are used in many applications for adjusting the rate of flow of gases and liquids. A typical throttle valve regulates the flow of a liquid or gas by adjusting the position of a plunger relative to a valve housing. A particular application of throttle valves is in regulating the flow of gases in a semiconductor processing chamber. In such a throttle valve, linear movement of the plunger relative to the valve housing is accomplished by a lift screw mechanism. The lift screw mechanism transfers rotational movement of a threaded screw into linear movement of the plunger.
FIG. 1
depicts a simplified, partial cross-sectional view of a prior art throttle valve assembly
50
that employs a lift screw mechanism
103
coupled to a throttle valve
100
. The throttle valve
100
comprises a valve housing
102
containing a plunger
104
. The plunger
104
moves linearly relative to the valve housing
102
to regulate the flow of a liquid or gas from an inlet (not shown) through the housing
102
to an outlet (not shown). In the prior art throttle valve assembly
50
, a hollow tube
107
extends from the plunger
104
. A threaded nut
105
is fixed to an end of the tube
107
. The nut
105
receives a threaded drive screw
106
with the end of the drive screw
106
extending into the tube
107
. The drive screw
106
is coaxially aligned with an axis
101
. A bearing
108
is affixed to the housing
102
. The rive screw
106
rotates freely in the bearing
108
. As the rive screw
106
rotates about the axis
101
the threads of the drive screw engage the threads of the nut
105
thereby imparting a linear motion to the plunger
104
along the axis
101
. As the plunger
104
moves upward, the drive screw
106
is received in the tube
107
.
Motive power for rotating the screw
106
is provided by a motor
118
such as an electric motor. A first pulley
110
is attached to a distal end of the drive screw
106
. A drive belt
112
is looped about the first pulley
110
and a second pulley
114
. The second pulley
114
is attached to a drive shaft
116
of the motor
118
. The drive shaft
116
is aligned with a drive axis
55
that is substantially parallel to the axis
101
. The motor
118
is fixed relative to the valve
100
such that rotation of the drive shaft
116
imparts motive power to the drive screw
106
via the pulleys
110
and
114
and the drive belt
112
.
In the prior art throttle valve assembly
100
, the axes
101
and
55
must be precisely aligned. A misalignment of the axes
101
and
55
(i.e., the axes are not parallel) will cause the drive shaft
116
to exert a bending stress on the drive screw
106
. The bending stress causes a bending strain on the drive screw leading to wear that seriously shortens its useful life.
Therefore, a need exists in the art for a lift screw mechanism for a throttle valve assembly in which the drive screw is not required to be exactly parallel with the drive axis.
SUMMARY OF THE INVENTION
The disadvantages associated with the prior art are overcome by the present invention of a self aligning lift screw mechanism having a driving member coupled to a drive coupler by a universal coupler. The universal coupler relieves a bending strain between the driving member and the drive coupler due to misalignment between the driving member and the drive coupler. Preferably, the driving member is a threaded drive member such as a drive screw, lead screw or ball screw. If a threaded drive member is used, the drive coupler is coupled to the universal coupler by a nut, threaded collar or ball nut that engages the threads of the driving member. Rotation of the driving member about its axis imparts axial movement to the drive coupler along the axis of the driving member. A motor, such as a stepper motor, is directly coupled to the driving member for imparting rotational movement to the driving member.
The universal coupler comprises an outer cylinder and first and second inner cylinders disposed within an axial bore in the outer cylinder. Each of the inner cylinders also has an axial bore. All three cylinders and all three bores are substantially coaxially aligned. The first and second inner cylinders have approximately the same outer diameter and are substantially coaxially aligned with one another. The first and second inner cylinders are pivotally connected to the inner surface of the outer cylinder. The driving member is coupled to the first inner cylinder and the drive coupler is coupled to the second inner cylinder such that pivotal movement of one or both of the inner cylinders avoids a bending strain between the driving member and the drive coupler.
Each inner cylinder is pivotally connected to the outer cylinder by a pair of opposed dowel pins, disposed between the inner cylinder and the outer cylinder. A first pair of dowel pins allows for pivotal movement of the first inner cylinder about a first pivot axis perpendicular to a cylinder axis of the outer cylinder. A second pair of dowel pins allows for pivotal movement about a second pivot axis perpendicular to both the axis of the outer cylinder and the first pivot axis.
In an illustrative embodiment of the invention, the lift screw mechanism is part of a throttle valve assembly. The valve assembly generally comprises a valve body, a housing, a threaded driving member, a drive coupler, a plunger guide and a plunger. The plunger is received in the valve body and attached to the plunger guide. The threaded driving member is rotatably mounted at first and second ends within the housing. The drive coupler is adapted for translational movement substantially parallel to the drive member. The plunger guide is substantially aligned with the driving member and attached to the drive coupler such that linear motion of the drive coupler imparts linear motion to the plunger guide. The driving member is coupled to the drive coupler by, for example, the threaded collar and universal coupler. A flexible bellows, disposed about the plunger guide isolates an atmosphere side of the throttle valve from a vacuum side, i.e., the side that is inside the bellows containing the chamber environment and its various gases. The bellows are sealed at a first end to a cap on the valve body and sealed at a second end to the plunger.


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patent: 5562360 (1996-10-01), Huang
patent: 6056262 (2000-05-01), Mazur
patent: 2 511 113 (1983-02-01), None
patent: 2 318 630 (1998-04-01), None

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