Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY ACTUATOR HAVING
INT~GRAL PISTO~ ASSEMBLY
WITH FLOATING RACK
TECHNICAL FIELD
This invention relates to rotary actuators
and more particularly to rotary actuators of t'ne
rack and pinion type.
A rotary actuator is a device which trans-
lates fluid energy into rotary motion. Essen-
tially, the rotary motion is accomplished by
applying fluid under pressure to a piston which is
inside a cylinder. Movement of the piston drives a
linear gear rack, which in turn drives a pinion
gear mated to it, imparting rotary motion to the
output shaf~. The output shaft is mounted between
two support bearings and is connected to a load,
either directly, through a coupling, or by linkage.
Rotary actuators are known to provide economical,
energy-efficient power converters for numerous
applications. They come in various sizes having
different rotations and torque outputs. A very
precise degree of rotation of the pinion and the
output shaft can be obtained by appropriate choice
of rack length and pinion diameter.
BACKGROUND ART
Various constructions of rack and pinion
type rotary actuators are known. For example, U.
S. Patent No. 3,246,581 to Carr illustrates one
such construction. The actuator shown in the Carr
patent has a rack assembly and a pair of pistons
which are connected by pins in such a way as to
form a 106t motion connection, so that the pistons
are free to float a limited distance relative to
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the rack assembly. The rack assembly includes a
number of pieces which must be secured together.
Such construction is relatively expensive to manu-
facture and assemble. Also, the pins must be
removed whenever a rack is to be replaced.
One-piece rack and piston assemblies in
rotary actuators are known. Constructions of this
type are shown, for example, in Steiner U. S.
Patent 2,844,128, Meyer et al u. s. Patent
3,156,160 and Carr U. S. Patent 3,213,760. One
piece rack and piston assemblies such as those
shown in these patents are relatively inexpensive
to manufacture compared to the multiple piece
arrangement such as that shown in Carr U. S. Patent
3,246,581 cited above. However, a floating piston
is desirable for some services and one-piece rack
and piston assemblies do not necessarily meet this
requirement.
DISCLOSURE OF INVENTION
It is an object of this invention to pro-
vide a rotary actuator having a minimum of moving
parts.
A more specific object is to provide a
rotary actuator having a floating rack but with a
minimum of moving parts.
A further object is to provide a rotary
actuator which is easy to assemble and in which the
rack can be quickly and easily replaced.
These and other objects are accomplished
by providing a reciprocable rack and piston
assembly comprising a one-piece rack insert in
which a rack and rack bearing are integrally joined
and/or are one and the same, and a one-piece piston
member having a piston at each end, means
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connecting the two pistons and means for retaining
said rack insert in such manner that the rack
insert is free to float in any direction except
longitudinally but is constrained from longitudinal
movement.
BRIEF DESCRIPTION OF DRA~INGS
IN THE DRAWINGS:
Fig. 1 is a front elevational view with
parts shown in section, of a rotary actuator
embodying the novel rack and piston assembly of
this invention.
Fig. 2 is a sectional view taken along 2-2
of Fig. 1.
Fig. 3 i5 a front elevational view of the
novel cast rack and piston assembly of this inven-
tion.
Fig. 4. is a sectional view taken along
line 4-4 of Fig. 3.
Fig. 5 is a bottom view of the piston
member of this invention.
BEST MODE FOR CARRYING OUT THE INVENTION
This invention will be described with
particular reference to a fluid operated, double
acting rotary actuator of the rack and pinion type,
although it will be understood that this invention
is also applicable to other types of rack and
pinion rotary actuators.
Referring now to Figs, 1 and 2, 10 indi-
cates generally an air operated rotary actuator of
the rack and pinion type. Rotary actuator 10 has a
housing 12 having an inside wall of circular cross
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section and an outside wall of square or rectan-
gular cross section. The two ends of housing 12
are closed by end caps 14. Housing 12 and end caps
14 together form a chamber for a pinion and for the
novel rack and piston assembly of this invention,
as will be hereafter described. This chamber
includes a longitudinally extending piston bore
12a, which is formed by the inside wall of housing
12, and in which the rack and piston assembly
reciprocates. Sealing rings 15 provide a fluid
tight seal between the housing 12 and the end caps
14. Bolts 16 secure the end caps to housing 12.
Each of the end caps 14 has a central port
18 for the admission of fluid under pressure. As
will be described later, the rotary actuator 10 is
driven by alternately admitting fluid under
pressure first to one end of the rotary actuator
and then to the other, in each case through a port
18. The exterior of housing 12 may be provided
with screw-threaded bores 19 for mounting bolts.
These bores do not extend to the interior of the
housing.
Rotary actuator 10 is symmetrical about
the line 2-2 in Fig. 1.
Rotary actuator 10 also has a pinion 20
and a pinion journal 20a, which are mounted in
direct drive relationship. Pinion 20 drives an
output shaft 22. Shaft 22 has a key 23. Shaft 22
may extend in both directions through an opening 24
in housiny 12. This opening is located midway
between the two ends of the rotary actuator lQ.
One end of shaft 22 terminates inside the housing
12.
Pinion journal 20a is mounted for rotation
in bearings 26. Bearings 26 are held in place by
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thrust washers 30 and bearing retainers 32.
O-rings 34 prevent leakage between the pinion
journal 20a and bearing 26, while O-rings 36
prevent leakage between bearing 26 and housing 12.
The rotary actuator of this invention has
a novel two-piece rack and piston assembly 40 which
reciprocates in bore 12a. Rack and piston assembly
40 co~prises a replaceable rack insert 42 and a
one-piece reciprocable piston member 44.
Rack insert 42 is a one-piece member, and
is preferably a metal casting in which a rack and a
rack bearing are integrally joined and/or are ~ne
and the same. The top o~ rack insert 42 has a
plurality of teeth which engage mating teeth on
pinion 20. The bottom of rack insert 42 is cylin-
drical in shape and fitted to the cylindrical
inside wall of rotary actuator lO. The bottom of
rack insert 42 is a bearing surface which slides
smoothly in the rotary actuator chamber. Rack
insert 42 also includes a pair of tangs 42a, one at
each end, for engaging piston member 44.
A wide rack insert 42 and pinion 20 are
preferred. This makes it possible to use lower
strength and less expensive materials than would
normally be required. A wide rack insert alsG pro-
vides a large bearing area between the rack insert
42 and the inside wall of housing 12.
The length of the rack insert 42 is deter-
mined by the maximum number of degrees of desired
rotation of the pinion 20 and its associated shaft
22. Rotations of either 90 degrees or 180 degrees
are the most widely desired, although any desired
degree of rotation may be obtained by appropriate
selection of pinion diameter and rack length.
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The one-piece piston member 44 will be
described with particular reference to Figs. 3, 4
and 5. Piston member 44 comprises at least one
piston and means for engaging rack insert 42,
thereby causing rack assembly 42 to reciprocate as
piston member 44 reciprocates.
The preferred piston member 44 is a
one-piece precision cast metal member as shown in
the drawings and particularly in Figs 3, 4 and 5.
Piston member 44 includes two pistons 46, one at
each end, a pair of rack-retaining lugs 47 which
extend inwardly from each piston toward the other
and which form slots 47a to receive tangs 42a, and
a support strut 48 which extends from one piston to
the other and thereby connects the two pistons.
Pistons 46 have grooves 50 to receive sealing rings
52 (see Fig. 13.
Lugs 47 engage the ends of rack insert 42
so that there is a snug fit between rack insert 42
and piston assembly 44. Rack insert 42 is free to
float in any direction except longitudinally but is
constrained from longitudinal movement (i.e., move-
ment toward one of the end caps 14). This floating
arrangement prevents forces transmitted by pinion
20 to rack insert 42 from being Eurther transmitted
to piston member 44. Instead, the separation force
from the pinion will drive the rack insert against
the cylinder wall but will not have any tendency to
cock the piston member. This arrangement also
makes the rack insert 42 self-aligning with respect
to pinion 20.
When fluid pressure is applied to the left
end of rotary actuator 10, the rack insert 42 and
piston assembly 44 move as a unit to the right;
conversely, application of fluid pressure to the
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right end of rotary actuator 10, causes the rack
insert 42 and piston assembly 44 to move as a unit
to the left.
There is no attachment means (such as a
pin or the like) betw~en piston member 44 and rack
insert 42. Instead, piston member 44 drives rack
insert 42 by direct contact between the two. This
arrangement makes it easy to replace rack insert
42.
The piston material is one which can be
cast and machined readily. A minimum of machining
is required since the member may be cast to desired
shape.
Various options not illustrated herein may
be provided if desired. For example, a fluid
cushion such as that illustrated in U. S. Patent
3,213,760 to Carr may be provided to cushion the
movement of rack and piston assembly 40 as it
approaches either end of travel. Also, the limit
of rotation of output shaft 22 may be adjusted by
providing an adjustable stop such as that shown on
page 10 of the brochure, "FLO-TORK Rotary Actua-
tors" (FLO-TORK, Inc., Orrville, Ohio, 1984).
The piston member of this invention is
light in weight and capable of manufacture at low
cost with a minimum of machining. The piston and
rack assembly provides a larger bearing area and
wider tooth contact than do rack and rack bearing
structure in presently known rotary actuators. A
rotary actuator containing this piston member is
easy to assemble because the rack insert and the
piston member together comprise only two pieces, in
contrast to the multiplicity of pieces required in
typical floating piston rotary actuators known in
the art. Also, the present construction permits
quick and easy replacement of the rack insert.
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While in accordance with the Patent
statutes only a preferred embodiment has been
illustrated and described in detail, it is to be
particularly understood that the invention is not
limited thereto or thereby.
