Expansible chamber devices – With linkage or transmission engaging portion intermediate...
Reexamination Certificate
1998-11-03
2001-02-20
Ryznic, John E. (Department: 3745)
Expansible chamber devices
With linkage or transmission engaging portion intermediate...
Reexamination Certificate
active
06189436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to fluid power rotary actuators, and in particular to a radial bellcrank actuator.
2. Background of the Invention
Fluid power actuators enjoy considerable popularity in a wide variety of industrial applications, especially in automation and numerical control machines. Either pneumatic or hydraulic fluid may be used to power these actuators.
The most common applications for rotary actuators are in automation where they perform functions such as turning valves, rotating products, positioning diverting arms, bending products, etc. They are also used in animation, process control (primarily valve actuation), vehicle control such as rudders or flaps, robotics, agricultural and other mobile equipment, etc.
A typical rotary fluid power actuator system comprises a cylinder within which a piston is free to reciprocate. A pressurized fluid supply is alternately connected to either a first cylinder end or a second cylinder end through a directional control valve and cylinder ports. The piston is driven away from the cylinder end to which the pressurized fluid supply is connected. A flow control valve may be connected to each cylinder end to control the flow rate of fluid escaping from the cylinder ahead of the piston, which in effect controls the piston speed during most of the stroke.
Means is provided to convert the linear reciprocating motion of the piston into rotary motion of an output shaft, which is attached to the load to be moved. The rotary motion of the output shaft is rotationally reciprocal, and is generally limited to an amount less than one full rotation up to as much as a few rotations, rather than unlimited rotation as in the motion produced by a motor.
In operation, the directional control valve permits fluid at driving pressure to flow into a first cylinder end, which drives the piston towards an opposite, second cylinder end. The speed at which the piston travels toward the second cylinder end (and hence the speed of rotation of the output shaft) may be controlled by the rate at which fluid is allowed to escape from the second cylinder end through the flow valve associated with the second cylinder end.
Fluid power rotary power actuato applications can be divided into categories based on their degree of positioning control. The most basic system moves to stops at each end of a fixed stroke. It is normally controlled by a single valve having two states, one corresponding to each position of the actuator. The speed of motion may be controlled by adjustable metering valves acting on the fluid stream. The torque produced can be controlled by controlling the pressure of the fluid.
At the other end of the positioning control spectrum are infinitely positionable systems in which the fluid driving the actuator is controlled by a proportional or servo valve which is part of an active control system which includes position feedback. These systems require an actuator with little or no lost motion or backlash in order to achieve accuracy.
Between these two extremes are various levels of positioning capability. Some examples are adjustable stops to limit rotation, multiple stops based on additional cylinders integrated into the actuator (generally, each stop requires an additional valve for control), and cushions which decelerate the load near the end of rotation.
EXISTING DESIGNS
A number of rotary fluid actuator designs incorporating reciprocating pistons exist within the art. U.S. Pat. Nos. 5,492,050, 5,385,218 and 4,905,574 were granted to Holtgraver, Migliori, and Trevisan respectively for rack and pinion type actuators. In these designs, a piston(s) attached to a rack(s) reciprocates as urged by fluid pressure. The rack(s) meshes with a pinion shaft, whereby rack motion causes the pinion to rotate. One disadvantage associated with the rack and pinion design is the relative complexity and cost of the assembly.
Another rotary fluid power actuator is the cable, chain or belt design. This design incorporates a flexible tension member connecting pistons which reciprocate within a cylinder, driven by fluid. The flexible member is wrapped around a pulley type member, which is attached to an output shaft, thus causing the output shaft to rotate.
The Scotch Yoke is another rotary fluid power actuator design which includes a piston reciprocating within a cylinder, pins protruding from the piston, and a yoke whose two extremes are rotatably attached to the piston pins by means of yoke slots. An output shaft is attached to the yoke, such that rotation of the yoke as urged by the piston causes the output shaft to also rotate.
U.S. Pat. No. 4,230,025 was granted Caliri for a helical drive rotary fluid power actuator. In this type of design, a piston slides within a cylinder as urged by fluid pressure. The piston and an output shaft are coaxial and have mutually mating helical features which convert the linear motion of the piston into rotary shaft motion.
Still another rotary fluid power actuator design is the barrel cam design. In this design, a piston slides in a cylinder driven by fluid pressure. The piston has a shaped slot in its outer surface which mates with a follower attached to an output shaft.
The designs described above all suffer from the disadvantages associated with complex machining required to fabricate their components. All require milling in addition to lathe work, and some require complex assembly tooling to accurately orient the various components relative to each other for attachment. These added assembly steps translate into additional assembly time, increased scrap if assembly is not accurate, and consequently, higher unit price.
Another existing rotary fluid power actuator design is illustrated in FIG.
1
.
FIG. 1
depicts L-bar rotary fluid power actuator
60
. In this design, piston
62
reciprocates within a cylinder as indicated by arrows
70
. Piston
62
comprises circumferentially disposed piston groove
64
. L-bar
66
is attached to output shaft
68
. L-bar
66
comprises L-bar major leg
74
rigidly attached to L-bar minor leg
76
. L-bar major leg
74
is rigidly attached perpendicular to the centerline of output shaft
68
. L-bar minor leg
76
is rigidly attached perpendicular to an extreme of L-bar major leg
74
opposite output shaft
68
, parallel to the centerline of output shaft
68
. In operation, reciprocation of piston
62
as indicated by arrows
70
causes output shaft
68
to rotate as indicated by arrow
72
.
There are a number of problems associated with the design of L-bar rotary fluid power actuator
60
. In order to make the required attachments, tooling must be constructed to hold L-bar major leg
74
in position perpendicular to output shaft
68
, and to hold L-bar minor leg
76
parallel to the centerline of output shaft
68
and perpendicular to L-bar major leg
74
. Then L-bar major leg
74
must be attached to output shaft
68
, and L-bar minor leg
76
must be attached to L-bar major leg
74
. In order to derive the necessary strength, these attachments must generally be made by welding or brazing. If the indexing of these parts is inaccurate, this actuator will not function correctly. Thus the L-bar rotary fluid power actuator
60
design suffers from complexity in assembly due to the number of parts involved, and the requirement for accuracy and exactness in assembling L-bar
66
, and attaching same to output shaft
68
. These manufacturing drawbacks translate into increased assembly time, resulting in higher unit price.
Another disadvantage associated with the L-bar rotary fluid power actuator
60
design is the small bearing area of L-bar minor leg
76
on piston groove
64
. This small bearing footprint results in increased wear, and/or the requirement that harder materials be used. The use of harder materials equates with increased cost. Still another disadvantage associated with this design is the asymmetrical loading to which L-bar
66
is subjected. In our non-frictionless world, friction (and load inertia) opposing the rotation of output shaf
Rooy P.A. Paul S.
Ryznic John E.
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