Low pressure actuator

Details Low pressure actuator Low pressure actuator

1998-07-09

2001-04-03

Look, Edward K. (Department: 3745)

Expansible chamber devices

Bellows type expansible chamber

Plural bellows

C092S136000

Reexamination Certificate

active

06209443

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to a novel low pressure mechanical actuator. More particularly, this invention pertains to a novel low pressure pneumatic or hydraulic device which creates a linear or radial mechanical force to move components, machinery or control valves.
BACKGROUND OF THE INVENTION
Mechanical actuators with pistons are widely used in industry for moving parts or components of machinery to carry out various functions. Actuators are used in assembly lines or industrial processes to control valves, or to operate equipment. Actuators usually operate using pneumatic or low pressure hydraulic fluid to create a force, linear or rotary, to move a component or piece of machinery.
Pneumatic pistons or actuators are of two basic types:
A. Bellows. These typically are hollow and consist of preformed rubber which extends and contracts in a linear manner by an “accordion” mechanism extending or collapsing the elastomer. To avoid radial bulging, the rubber must be very heavy, horizontal movement must be very short in relation to the radial dimension of the accordion shape, and pneumatic pressure must be sufficiently low so as not to rupture the rubber. Bellows type pistons are useful primarily for short thrust, low pressure movements such as switch or brake activation. Typical maximum working pressures of bellows type pistons are limited to about 20 psig.
B. Solid tube pistons. These actuators typically comprise a solid piston sliding within a hollow solid (usually metal) tube. Solid tube pistons typically operate at working pressures in the range of about 80 psig. To contain the required pneumatic force on the piston, one or more rubber air seals enclose the circumference of the piston and thereby contain the air. The air seals are similar to piston rings in an internal combustion engine. Typically, since the piston moves along the axis of the interior of the tubular cylinder, a linear force is generated. The term “actuator” is often applied in situations where a rotary (torque) force is to be generated. In the case of mechanical actuators, the rotational force is usually obtained by utilizing a rack and pinion arrangement within the cylinder. The rack is attached to the piston and the pinion exits the cylinder radially. This requires a seal (an O-ring, for example) to contain the air pressure. Various types of actuators are available, for example, double action and spring return.
The sliding piston in a fixed cylinder is commonly used for applications such as valve stem rotation. The inherent problem with this type is that they are expensive to manufacture and have wear and friction problems associated with the necessity for sliding seals on the pistons. Contaminated air can significantly shorten the life of the seals, and the design of such actuators does not permit economical serviceability. Some applications therefore require the air to be filtered or otherwise treated to prolong actuator service life.
Other linear movement mechanisms exist which comprise a tube that stretches in a linear manner, such as for air ducting used in ventilation systems. These stretchable tubular mechanisms include plastic tubing with embedded coiled wire which allows horizontal stretch of the tubing. The coiled wire provides radial strength. There is an inherent problem with such tubes. When a high pneumatic pressure is applied to the tube, it tends to turn and cause localized bulging. Such tubes with internal or embedded coils are thus suitable only for very low pressure applications.
Various inventors have attempted to solve the problems inherent in the designs of these two types of actuators by using a sealed rubber tube (air bag) and restraining its radial expansion by various means other than a bellows. These systems generally involve surrounding the rubber tube with an outer tube having helical wires. This allows the outside tube to stretch without bulging. Another method utilizes a second outside tube with compensating pneumatic pressure. These systems generally shorten the available stroke of the actuator relative to its length and also set up counteracting forces which significantly decrease the mechanical efficiency of the expanding inner tube.
Actuators usually employ one of two methods for activation:
A. The principle of physics that when pressure is applied to the inside surfaces of an “elastomer bag” of any shape (for example, an elongated balloon) the pressure will tend to force the bag into a spheroid shape. Thus the pressure attempts to equalize itself within the confines of the volume. This is described herein as “equalizing pressure”.
B. Restraining radial expansion of an elastomer bag by a series of two opposed diagonal windings for which the angle of the crossing points changes to allow some lengthening of the tube until a maximum angle change occurs. This is described as “radial constraint”.
A number of patents have been issued over the years disclosing various devices that employ one or the other, or both, of principles A and B above.
Beullens—U.S. Pat. No. 4,841,845
Beullens utilizes the equalizing pressure principle. This is demonstrated by the description of
FIGS. 1 and 2
as being in the inactive position and
FIG. 3
as being in the active position. Column 4, paragraph 40, discloses that “the working points . . . are pulled towards one another”. The purpose of the spiral wires in Beullens appears to be not only to stop the device from “blowing up” but also to redirect the radial force to a horizontal sucking force when maximum radial size is reached.
The device comprises on the one hand at least one tightly-sealable chamber, which is restricted by a wall made from a partially distortable material, and on the other hand flexible, approximately unstretchable spiral-wound filaments which extend substantially next to one another at least about said wall, whereby part of said filaments are wound rightwards and another part thereof leftwards, and this in such a way that two arbitrary crossing filaments may undergo some angular displacement relative to one another, and the one end of each said filaments on the one side of said chamber is fixed relative to a working point, and the other end thereof on the opposite side of said chamber is fixed relative to another working point, and whereby further at least one feed opening is provided in said chamber, wherethrough a pressurized gas or liquid may be fed and said wall is distortable at least along one direction cross-wise to the line joining both said working points, in such a way that by regulating the gas or liquid pressure inside the chamber, a relative displacement of said working points occurs.
Negishi—U.S. Pat. No. 5,201,262
Negishi utilizes the radial constraint principle. The actuator of Negishi includes an elastic member extensible in axial directions when a pressurized fluid is supplied into the elastic member, and a guiding device arranged inwardly of the elastic member and permitting the elastic member to move in the axial directions but restraining the elastic member from moving in directions intersecting the axial directions. The actuator is of an air-bag type so that energy of the pressurized fluid can be converted into mechanical movement with high efficiency. The actuator moves only in axial directions without expanding in radial directions, so that a space occupied by the actuator in operation is little. Due to the restrictions of angle change of the “reinforcing braided structure”, there is limited travel of this actuator in relation to its length. This limits its application. The other “embodiment” (
FIG. 3
a
) is the addition of a return spring outside the actuator.
Negishi—U.S. Pat. No. 5,158,005
The device disclosed by Negishi in this patent is very similar to the device in his U.S. Pat. No. 5,201,262, except that the guiding tube is now outside instead of inside. The actuator of this patent includes an elastic member extensible in axial directions when a pressurized fluid is supplied into the elastic member, and a guiding device arranged outwardly of the elastic member and

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