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Description  |
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FIELD OF THE INVENTION
The present invention relates to a hydraulic actuator. More particularly
this invention concerns an actuator usable to open and close a power
chuck.
BACKGROUND OF THE INVENTION
A power chuck, such as described in my copending application Ser. Nos.
40,126 (now abandoned); 40,127 (now U.S. Pat. No. 4,243,236); 40,128 (now
U.S. Pat. No. 4,243,237); 40,271; 40,272; and 40,433 (now abandoned), all
filed May 18, 1979, has a chuck body which is mounted on a lathe spindle
and is rotated thereby. Radially displaceable jaws on the chuck body are
all coupled to an actuating member which is displaceable axially relative
to the chuck body to radially displace the jaws thereof into or out of
engagement with a workpiece. Typically the lathe spindle as well as the
chuck are tubular so that rod stock can be fed axially through the spindle
to the chuck for serial production of like workpieces, in particular when
the lathe is operated as a screw machine.
A standard actuator, such as described in U.S. Pat. No. 2,835,227 or the
corresponding German patent publication No. 1,018,696 filed 8 March 1954
by L. Gamet, has an actuator body that is fixed to the chuck body, a
piston that is axially reciprocal within the actuator body and which is
connected to the actuating element of the chuck, and a connector body
which is rotatable on the actuator body and carries hydraulic connections
for pressurizing the compartments in the actuator body that axially flank
the piston. In this arrangement the piston is formed as a radially
projecting flange on a sleeve that is axially slidable within the actuator
body, and that in turn is fixed to another sleeve that extends axially out
of the actuator for connection to the actuating element of the chuck.
The connector body is mounted via roller bearing on the actuator body with
extremely small clearance in at least one location. At this location one
of the bodies is formed with circumferential grooves open toward the other
body which in turn is formed with radially extending passages aligned with
these grooves. The connector body has hydraulic connections connectable
via a valve to a source of fluid under pressure and a sump to pressurize
the compartments and operate the chuck by the actuator.
The hydraulic fluid or oil used to pressurize the compartments flanking the
piston therefore passes across a very narrow gap between the two bodies,
forming a boundary layer. As these two bodies fit together very well, but
without touching, this boundary layer acts as a fairly effective seal
between the passages relative to each other and between the passages and
the surrounding atmosphere. In fact the amount of leakage from this
boundary layer can be easily controlled so that it serves to lubricate the
working parts of the actuator.
The shear in this oil film, however, creates considerable heat. As the
radius between the film and the axis increases, the amount of shear also
increases considerably. Since such an actuator must normally form an
axially throughgoing passage, limits are set to reduction of this radius,
so that under the best of circumstances the radial spacing will be
relatively large.
As a result there is considerable heating of this boundary layer. It is
therefore common practice, as suggested in the above-cited German patent
publication, to provide the actuator and/or connector bodies with cooling
fins. Furthermore it is standard procedure to circulate the hydraulic
fluid through a cooler before returning it to the arrangement. The first
expedient has proven itself relatively ineffective in dissipating large
amounts of heat, and presents dangerous radially extending vanes on which
a lathe operator can be hurt. The second expedient is relatively
expensive, increasing first and operating costs.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved
power-chuck actuator.
Another object is to provide such an actuator which is not subject to the
above-described overheating problem.
SUMMARY OF THE INVENTION
These objects are attained according to the instant invention by providing
the actuator with fan means constituted as a fan carried on or coupled to
the actuator body. The connector body is formed with passages opening at
the intake or output side of this fan. When the two bodies rotate relative
to each other, therefore, air will be forced through these passages by the
fan to cool the actuator.
According to further features of this invention the connnector body has a
pair of concentric and radially spaced tube sections. The inner tube
section forms the outer wall of a compartment in which oil from the
boundary layer collects. The space between the inner and outer tubes opens
at its ends at arcuate slots. Heat-dissipating ribs bridge these slots,
and the fan is constituted as a multiplicity of radially extending vanes
carried on a wheel bolted directly on the back face of the actuator body.
These vanes are axially aligned with the slots at the other end of this
space between the two tube sections. Thus as the actuator body rotates
relative to the connector body the fan will suck air in through the space
formed between these two tube sections to effectively dissipate heat from
the connector body.
According to another feature of this invention the connector body is formed
with an axially forwardly projecting extension projecting beyond the space
in which the fan is provided. This extension is formed with a
circumferential array of angularly equispaced throughgoing holes
constituting a protective mesh or screen level with the fan. Thus the
outer surface of the actuator according to this invention will be
relatively smooth and free of projections, so that an operator of a
machine using such an actuator is not likely to hurt himself or herself on
the fan.
According to further features of this invention the actuator body is formed
centered on the axis with an inner axially forwardly extending annular
wall, with an outer axially forwardly extending annular wall forming with
the inner wall an annular chamber, and with an annular end wall generally
axially closing the chamber and having an inner periphery defining with
the inner wall an axially forwardly open annular slot. The piston
according to this invention is annular and axially forwardly and
backwardly displaceable in the chamber. It has an axially forwardly
projecting collar extending out of the chamber through the slot and having
an outer surface sealed against the inner periphery of the end wall, which
is advantageously bolted to the front edge of the outer wall, and an inner
surface sealed against the inner wall. Thus it is possible to reduce the
inner diameter of the connector body greatly, so that not only is heat
buildup minimized in the chuck according to this invention, but the heat
that is generated can readily be dissipated by the built-in fan.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an axial section through a power actuator according to this
invention; and
FIGS. 2 and 3 are sections taken respectively along lines II--II and
III--III of FIG. 1.
SPECIFIC DESCRIPTION
The power actuator according to this invention has a housing 1 formed
integrally with an annular outer wall 1.1 spaced relative to a central
axis outwardly from an annular inner wall 1.2. Bolts 1.3 secure a flat
cover plate 1.4 to the axial forward edge of the wall 1.1 to define a
front face 2 for the actuator body 1. Threaded holes 1.5 in the end plate
1.4 serve for mounting a power-chuck body to the end face 2. The body 1
therefore forms between the walls 1.1, 1.2 and 1.4 an annular chamber 3
subdivided by an annular piston 4 into a front compartment 3.1 and a back
compartment 3.2. This piston 4 has an axially forwardly extending collar 5
that extends axially forwardly out of the compartment 3 through a slot or
annular gap 6 formed between the cylindrical inner peripheral surface 7 of
the end plate 1.4 and the outer cylindrical peripheral surface 8 of the
inner annular wall 1.2. Seal rings 9 are provided to prevent leakage at
the gap 6. The sleeve or collar 5 is formed internally with a screwthread
10 into which the drive or actuating body of the power chuck to be
operated by this actuator is screwed. Axially extending antirotation pins
11 fixed in the body 1 pass through the piston 4 and prevent it from
rotating relative to the body 1.
In addition the body 1 is formed with an axially backwardly extending
sleeve 13 defining an axial passage 14 through the entire power actuator.
The inner diameter D of the collar 6 is approximately the same as that of
the passage 14, so that rod stock can be fed through the actuator as well
as through the power chuck operated by it in the manner well known in the
art, and of particular interest on lathes acting as screw machines.
A connector housing 16 is supported by axially spaced roller bearings 15 on
the sleeve extension 13 of the body 1, so that this connector housing 16
can rotate relative to the body 1 about the axis 12. Normally this
connector housing is held nonrotatable while the housing 1 rotates jointly
with the chuck it is attached to. The housing 16 is formed with a
cylindrical central bore 16.1 which is only at most few hundredths of a
millimeter larger in diameter than the outside diameter of the cylindrical
backward extension 13. In addition this housing 16 is formed with a pair
of axially spaced and radially inwardly open grooves 16.2 into which open
radially throughgoing passages 16.3.
The housing 16 also is provided with a pair of cap-shaped annular end
plates 16.5 defining annular passages 16.4 at the opposite ends of an
axially extending and centered compartment 16.6 into which the passages
16.3 open. A tube section 16.8 bridges the end caps 16.4 and defines the
outer wall of the compartment 16.6, with an oil-drain outlet 16.7 being
connected to this tube section 16.8. Normally the power actuator is
oriented with the axis 12 horizontal and the oil-drain outlet 16.7
directed downwardly. Another tube section 16.9 is placed between the end
plates 16.5 and lies outwardly of the tube section 16.8. Glands 16.10 are
provided at the ends of the annular passages 16.4.
A pair of hydraulic connection nipples 17.1 and 17.2 open at their inner
ends into respective radially inwardly open grooves 18.1 and 18.2 that
open into respective passages 19.1 and 19.2 (see FIG. 2) that in turn
communicate with respective axially extending passages 20.1 and 20.2 that
open into the compartments 3.1 and 3.2 of the piston chamber 3.
There is, therefore, fluid flow across the gap 21, having a radial
dimension of at most a few hundredths of a millimeter, between the
connector housing 16 and the body extension 13. Any oil leaking axially
along the interface between the two parts will flow into the radial
grooves 16.1 and 16.2 flanking the two grooves 18.1 and 18.2, and thence
will flow out through the radial passages 16.3 into the compartment 16.6,
whence the oil can drain off through the drain 16.7.
The two tube sections 16.8 and 16.9 define an annular axially extending
passage 22 opening externally at its axial ends through arcuate holes 23
best seen in FIG. 2. The two bodies 1 and 16 form between their axially
confronting ends a radially outwardly open groove or space 28. An annular
fan ring 24 is screwed to the rear face 27 of the chuck body 1 in this
space 28 and has a plurality of vanes 24.1. In addition the connector
housing 16 is formed with an axially forwardly projecting extension 25
formed with a multiplicity of radially throughgoing holes 25.1 axially
level with the vanes 24.1 and constituting a protective screen for the fan
24. Thus rotation of the chuck body 1 about the axis 12 at high speed
relative to the connector body 16 will cause the fan 24 to suck air
axially in through the rear holes 23, then through the compartment 22,
then through the front holes 23, and will expel the air radially outwardly
through the holes 25.1, thereby cooling the connector body 16. To aid in
heat dissipation ribs 26 are formed in the body 16 that bridge the
openings 23 as shown in FIG. 2. The faster the relative rotation of the
two bodies 1 and 16, the greater will be the air throughput through the
chamber 22, compensating for the greater heat development at higher speed.
Thus the actuator according to this invention is self-cooling.
FIG. 3 shows how the chuck is provided with a double-safety valve 30
comprised of a pair of cages 30.1 and 30.2 housing respective valve balls
31.1 and 31.2 biased by respective compression springs 32.1 and 32.2
against respective seats 33.1 and 33.2. A control piston 34 is chordally
displaceable betweeen the two balls 31.1 and 31.2 and can displace either
of these balls away from its respective seat. The ball 31.1 therefore
forms a check valve normally effective to prevent flow from the passage
20.1 to the passage 19.1, and the ball 31.2 normally acts as a check valve
preventing flow backwardly from the passage 20.2 to the passage 19.2. So
long as the piston 34 remains in the illustrated central position flow out
of either of the chambers 3.1 and 3.2 is impossible.
When, however, one of the passages 19.1 or 19.2 is pressurized the chamber
between the respective valve ball 31.1 or 31.2 and the piston 34 will
become pressurized, so as simultaneously to lift the respective ball off
its seat, and to push the piston 34 in the opposite direction to lift the
other ball off its seat also. For example if the passage 19.1 is
pressurized the ball 31.1 will be lifted off its seat 33.1 by the pressure
effective upwardly, as seen in FIG. 3, against it, while the piston 34
will be pressed downwardly by the same pressure to move the ball 31.2
downwardly away from its seat 33.2.
This safety-valve structure 30 therefore ensures that absent positive
actuation of the chuck by pressurization of one of the passages 19.1 or
19.2 via the respective connection 17.1 or 17.2, the piston 4 would be
unable to move in the chamber 3. Thus if for some reason or other pressure
is lost, the chuck operated by the actuator according to this invention
will not automatically loosen, but will remain locked on its workpiece.
This expedient therefore makes the system substantially safer, and even
allows the pressure to the actuator to be cut off, if necessary, once the
chuck has been adequately tightened on the workpiece.
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