Pneumatic actuator

Details Pneumatic actuator Pneumatic actuator

1999-04-07

2001-11-20

Kaufman, Joseph A. (Department: 3754)

Valves and valve actuation

Fluid actuated or retarded

Rotary or oscillatory motor

C092S120000, C092S121000, C092S124000

Reexamination Certificate

active

06318701

ABSTRACT:

FIELD OF INVENTION
The present invention is concerned with the field of valves and actuators and relates to a pneumatic actuator. More particularly, the present invention is an improved pneumatic actuator, which includes a rotary piston that is reciprocally received in a housing with a seal member securely mounted to an inner periphery of the housing wherein the rotary piston is slidably moved over the seal member.
BACKGROUND OF INVENTION
FIG. 1
shows a conventional pneumatic valve actuator which includes a toothed shaft
10
, an actuating shaft
20
extending through the toothed shaft
10
, two piston members
30
each having a rack member
301
engaged with the toothed shaft
10
, and a plurality of springs
302
biasedly disposed between an inner side of a housing
40
and the piston members
30
. In operation, the pneumatic valve actuator operates on the basis of cycles of air movement. At the beginning of a cycle air under pressure enters the interior of the housing
100
via two holes
41
to push the piston members
30
from a starting position away from each other to a fully separated position (as illustrated in
FIG. 1
) such that the toothed shaft
10
is rotated in a counter-clockwise direction by the movement of the two rack members
301
and the springs
302
are thereby compressed. By virtue of the rotation of the toothed shaft the actuating shaft
20
is also rotated. The rotation of the actuating shaft
20
is utilized for some other function (not shown). When the piston members
30
reach the fully separated position air entry into the housing is stopped, and the two holes
41
are opened to vent the housing at which time, the springs
302
push the piston members
30
back to the original starting position and thereby the toothed shaft
10
, and correspondingly, shaft
20
are rotated in the clock-wise direction. When the piston members reach the starting position, one cycle will have been completed. During operation, the force of pressurized air in the housing
100
causes leakage at the positions where the toothed shaft
10
and/or the actuating shaft
20
extend through the housing
40
(not shown in FIG.
1
). Depending upon the construction characteristics and materials used in the valve, as well as the amount of pressure, even after using such actuators for a short period of time leakage can occur. Furthermore, the interior surfaces of the housing
40
and contact and sliding surfaces of the rack members
301
must be manufactured precisely to ensure that the rack members
301
slides smoothly along the inner surfaces of the housing
40
all of which increases the cost of manufacturing.
Another commonly used pneumatic valve actuator is illustrated in
FIGS. 2 and 3
. The actuator
6000
is disposed between a return spring
7400
and a valve
7200
with a shaft
6200
extending through the return spring, the actuator and the valve so that when pressurized air is injected into the actuator, the shaft is rotated to operate the valve.
The actuator includes a casing, including an upper casing
6010
, a lower casing
6020
and a vane member
6400
which is received between the upper and lower casing. The upper and lower casing are connected by bolts
6030
along flanges extending from each of the upper and lower casing wherein the lower casing has two passages
6800
defined therein so that pressurized air can be injected from the air pump and into the passages. The shaft rotatably extends through the upper casing and the lower casing and securely extends through the vane member. A seal member
6600
is disposed to the vane member so that the piston member is reciprocally moved within the casing by pressurized air entering the casing through the passages. The shaft is co-rotated with the vane member so as to control the actuator between an open and closed position. A return spring means
7400
including a spring coil
7600
is disposed above the actuator casing in accordance with a requirement to automatically return the shaft to its starting position once the pressurized air is stopped, thereby returning the vane to its original position.
The seal member tends to become quickly worn out because the seal member slides along a inner surface of the casing whenever the piston moves. Furthermore, the inner surface of each of the upper and lower casing must be machined smooth to prolong the life of the seal. The return means including the coil spring and the machining of the inner surface of the casing results in the whole assembly being quite expensive.
SUMMARY OF THE INVENTION
The present invention avoids the above-noted problems of the prior art by providing an improved pneumatic actuator comprising a simpler, cost efficient piston, spring, and seal assembly.
Accordingly, the present invention provides a pneumatic actuator comprising a housing having an inner surface, a piston having an exterior surface and disposed within the housing, a shaft connected to piston, and a seal simultaneously engaging each of the exterior surface of said piston, the inner surface of said housing, and the shaft, and defining first and second chambers within the housing. The first chamber can be substantially isolated from the second chamber. The seal can further include aperture means for receiving the shaft. The exterior surface of the piston can be movable relative to the seal. The seal can immovably reside in a groove formed within the inner surface of the housing. Movement of the piston from a static condition to an operative condition can be effected by fluid pressure. The actuator can further comprise resilient means for biasing the piston towards a static condition. The resilient means can have a first end and a second end, the first end engaging an inner surface of the housing within the second chamber, and the second end engaging the piston, and could include a leaf spring. The actuator can be operatively connected to a valve to effect movement thereof.
In another aspect, the present invention provides a pneumatic valve actuator comprising a housing, a piston, moveable between a stable condition and an operative condition, a seal for effecting sealing between the piston and the housing, and defining first and second chambers within the housing, and resilient means disposed within the housing for biasing the piston towards a static condition. The first chamber can be substantially isolated from the second chamber. The resilient means has a first end and a second end, the first end engaging an inner surface of the housing within the second chamber, and the second end engaging the piston. The actuator can be operatively connected to a valve to effect movement thereof.
In yet another aspect, the present invention provides a pneumatic actuator comprising a housing, a piston having an exterior surface, means to introduce fluid pressure into the housing to effect movement of the piston, and a seal for effecting sealing between the piston and the housing, and defining a first chamber and a second chamber within the housing, the seal engaging the exterior surface of the piston in a substantially fluid tight arrangement in response to fluid pressure in the first chamber. The seal can have a surface exposed to fluid pressure within the first chamber, the fluid pressure acting upon the surface to effect a substantially fluid tight engagement between the seal and the exterior surface of the piston. The surface of the seal is other than perpendicular relative to an axis to an axis defined by the exterior surface of the piston. The actuator can be operatively connected to a valve to effect movement thereof.
In a further aspect, the present invention provides a pneumatic valve actuator comprising a housing, a rotary piston having at least a top-side, a bottom-side and a peripheral wall, sealing means, wherein the sealing means is cooperatively arranged with the housing and the piston such that the sealing means is in contact with the top, bottom and peripheral wall of the piston and the housing and thereby defines a first and second chamber within the housing, means for effecting moveme

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