U.S. patent number 3,695,116 [Application Number 05/076,952] was granted by the patent office on 1972-10-03 for non-explosive electrically initiated heat-ignitable actuator.
This patent grant is currently assigned to The Bunker-Ramo Corporation. Invention is credited to Robert Baur.
United States Patent |
3,695,116 |
Baur |
October 3, 1972 |
NON-EXPLOSIVE ELECTRICALLY INITIATED HEAT-IGNITABLE ACTUATOR
Abstract
A non-explosive, electrically initiated, heat-ignitable actuator
constructed and arranged in the form of a biased, collapsible dual
piston assembly. When the actuator is in the unactuated condition,
the dual piston assembly is prevented from collapsing by an
electrically triggerable dual shear pin and associated
heat-ignitable wire arrangement. The shear pins and their
associated wires are composed of a primarily alluminum and
palladium bimetallic composition which when ignited produces a
violent but non-explosive reaction which rapidly propagates to all
portions of the material. The construction of the dual piston
assembly is such that ignition of either or both of the shear pins
causes the piston assembly to collapse and thereby bring about
actuation of the actuator.
Inventors: |
Baur; Robert (Los Angeles,
CA) |
Assignee: |
The Bunker-Ramo Corporation
(Oak Brook, IL)
|
Family
ID: |
22135192 |
Appl.
No.: |
05/076,952 |
Filed: |
September 30, 1970 |
Current U.S.
Class: |
74/2 |
Current CPC
Class: |
B64D
17/32 (20130101); B64D 1/06 (20130101); F42B
3/006 (20130101); Y10T 74/11 (20150115) |
Current International
Class: |
B64D
1/00 (20060101); B64D 17/00 (20060101); B64D
1/06 (20060101); B64D 17/32 (20060101); F42B
3/00 (20060101); G05g 017/00 () |
Field of
Search: |
;74/2 ;89/1B
;337/401,220 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kaufman; Milton
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A non-explosive, electrically initiated, heat-ignitable actuator
comprising:
a housing,
a collapsible piston assembly disposed within said housing,
at least one heat-ignitable shear pin cooperating with said
collapsible piston assembly to prevent collapse thereof, and
initiating means for igniting said shear pin in response to an
applied electrical signal.
2. The invention in accordance with claim 1, wherein said shear pin
is in the form of a hollow cylinder and said initiating means
includes a heat-ignitable wire passing through said cylinder for
causing ignition of said shear pin as a result of said wire being
ignited in response to said electrical signal being applied
thereto.
3. The invention in accordance with claim 1, wherein said shear pin
and wire are of a heat-ignitable material which when brought to
ignition temperature produces a violent and rapidly propagating but
non-explosive reaction resulting in disintegration of the
material.
4. The invention in accordance with claim 1, wherein said
heat-ignitable material is a bimetallic composition comprised
primarily of aluminum and palladium.
5. The invention in accordance with claim 1, wherein said shear pin
is formed by rolling a foil of said heat-ignitable material onto
said wire so as to form a cylinder encircling said wire.
6. The invention in accordance with claim 1, wherein said wire is
provided with a substantially reduced diameter portion at a
predetermined location thereof in order to establish an initial
starting point for ignition of the wire in response to the applied
electrical signal.
7. The invention in accordance with claim 1, wherein a second
heat-ignitable shear pin is provided cooperating with said
collapsible piston assembly so that ignition of either shear pin
permits collapsing of said assembly.
8. The invention in accordance with claim 1, wherein said
collapsible piston assembly includes first and second pistons whose
movements within said housing are respectively prevented by the
shear pins.
9. The invention in accordance with claim 1, wherein said shear
pins are of a heat-ignitable material which when brought to
ignition temperature produces a violent and rapidly propagating but
non-explosive reaction resulting in disintegration of the material,
and wherein said initiating means includes a heat-ignitable wire of
said material cooperating with each shear pin for causing ignition
thereof as a result of said wire being ignited in response to said
electrical signal being applied thereto.
10. A non-explosive electrically initiated, heat-ignitable actuator
comprising:
a housing,
a collapsible dual piston assembly disposed within said
housing,
first and second heat-ignitable members cooperating with said dual
piston assembly in a manner so as to prevent collapse thereof so
long as neither member is ignited, and
initiating means for igniting said members in response to an
applied electrical signal.
11. The invention in accordance with claim 10, wherein said
collapsible dual piston assembly includes inner and outer pistons
and a body portion, said outer piston being movable with respect to
said housing and said inner piston being disposed between said
outer piston and said body portion and being relatively movable
with respect to both, one of said heat-ignitable members being
disposed so as to prevent relative movement between said inner
piston and said outer piston and the other of said heat-ignitable
members being disposed so as to prevent relative movement between
said inner piston and said body portion.
12. The invention in accordance with claim 11, wherein said members
are each provided as a shear pin, and said initiating means
includes first and second heat-ignitable wires cooperating with
respective ones of said shear pins for causing ignition thereof as
a result of its respective wire being ignited in response to said
electrical signal being applied thereto.
13. The invention in accordance with claim 12, wherein each shear
pin is provided in the form of a hollow cylinder through which its
respective wire is passed.
14. The invention in accordance with claim 12, wherein said shear
pins and wires are of a heat-ignitable material which when brought
to ignition temperature produces a violent and rapidly propagating
but non-explosive reaction resulting in disintegration of the
material.
15. The invention in accordance with claim 11, wherein said outer
piston is slidably movable within said housing and said inner
piston has its end portions slidably movable in respective bores
provided in said outer piston and said body portion, and wherein
one of said members is disposed so as to prevent relative movement
of said inner piston in the bore of said outer piston and the other
of said members is disposed so as to prevent relative movement of
said inner piston in the bore of said body portion.
16. The invention in accordance with claim 15, wherein said members
are each provided as a shear pin, and said initiating means
includes first and second heat-ignitable wires cooperating with
respective ones of said shear pins for causing ignition of each as
a result of its respective wire being ignited in response to said
electrical signal being applied thereto.
17. The invention in accordance with claim 16, wherein said shear
pins and wires are of a heat-ignitable material which when brought
to ignition temperature produces a violent and rapidly propagating
but non-explosive reaction resulting in disintegration of the
material.
18. The invention in accordance with claim 16, wherein said
heat-ignitable material is a bimetallic composition comprising
primarily aluminum and palladium.
19. The invention in accordance with claim 16, wherein said housing
also includes means for maintaining the uncollapsed dual piston
assembly in a fixed position in said housing.
20. The invention in accordance with claim 19, wherein said housing
includes means adapted to receive an applied force acting so as to
urge the respective ends of said inner piston more deeply into
their respective bores against the restraint provided by their
respective shear pins, and wherein the ends of said inner piston
are each able to move a sufficient distance into their respective
bores so as to cause the piston assembly to collapse by at least a
predetermined minimum amount in response to an applied force if at
least one of said shear pins is ignited.
21. The invention in accordance with claim 20, wherein said
initiating means includes lead-in wires fed into said housing and
electrically connected to said heat-ignitable wires so as to permit
applying an initiating current thereto sufficient to cause ignition
thereof.
22. The invention in accordance with claim 21, wherein each
heat-ignitable wire has a greatly reduced diameter at a
predetermined location for establishing a starting point for
ignition thereof in response to an applied initiating current.
23. The invention in accordance with claim 21, wherein said housing
also includes means for sealing said piston assembly therein.
24. The invention in accordance with claim 16, wherein means are
additionally provided responsive to the collapse of said piston
assembly for initiating the performance of a mechanical operation.
Description
BACKGROUND OF THE INVENTION
The present invention relates to fast acting, electrically
initiatable actuators capable of providing relatively large
mechanical forces. Such an actuator may be desired, for example, in
order to provide for physically moving a mechanical member in
response to an electrical initiating signal so as to initiate the
automatic actuation of a remotely located mechanical device.
Known electrically initiatable actuators are of various types.
Certain types involve the use of magnetic solenoid or
servomechanism devices which have the disadvantages of being
expensive, bulky, slow-acting and/or requiring excessive power.
Other known types of actuators are of an explosive nature involving
the use of explosive squibs, bridge-wire initiators, frangible
diaphragms and similar devices of an explosive nature. While such
explosive actuators may be made smaller and at less expense, they
are more dangerous to use, handle, and test.
More recently developed types of electrically initiatable actuator
devices have attempted to avoid the use of explosive actuation
while retaining its advantages. Typical ones of such devices are
described, for example, in U.S. Pat. Nos. 3,163,732 and 3,359,804.
In a typical device of this nature a spring is maintained in a
loaded condition by an electrically responsive keeper wire in axial
tension. The construction and arrangement of the keeper wire is
caused to be such that, when an electrical current of sufficient
magnitude is caused to flow in the wire, the resulting heating
causes the axial tensile strength of the wire to decrease below
that required to retain the spring. The weakened keeper wire thus
breaks and releases the spring to actuate any suitable device.
While devices of this type are able to avoid the use of explosive
actuation, they have been found to be of marginal reliability,
relatively slow-acting, and/or relatively complex.
SUMMARY OF THE INVENTION
In an exemplary embodiment of an improved actuator in accordance
with the invention, the above referred to disadvantages of prior
art actuators are to a very great extent overcome by the provision
of a non-explosive electrically initiated heat-ignitable actuator
provided in the form of a biased, collapsible dual piston assembly.
In the unactuated condition, the two pistons making up the dual
piston assembly are prevented from collapsing by a pair of spaced
heat-ignitable shear pins cooperating with respective ones of the
pistons. Each shear pin is triggered by applying an appropriate
initiating current to a respective heat-ignitable wire associated
therewith. The heat-ignitable shear pins and their associated
heat-ignitable wires are made from a bimetallic heat-ignitable
composition comprised primarily of palladium and aluminum which
when brought to ignition temperature produces a violent, but
non-explosive, rapidly propagating reaction which results in a
disintegration of all parts of the material. The collapsible dual
piston assembly has a construction such that ignition of either or
both of the shear pins will cause the assembly to collapse and
thereby bring about actuation of the actuator.
The specific nature of the invention as well as the objects,
advantages and features thereof will become apparent from the
following description of a preferred embodiment thereof taken in
conjunction with the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an axial cross-sectional view of a typical embodiment of
a non-explosive electrically initiatable actuator in accordance
with the invention, the actuator being illustrated in its
unactuated condition.
FIG. 2 is an axial cross-sectional view taken along the line 2--2
in FIG. 1.
FIG. 3 is an exploded perspective view of the actuator illustrated
in FIGS. 1 and 2.
FIGS. 4 - 6 are axial cross-sectional views illustrating relative
positions of the actuator elements prior to and after
actuation.
FIGS. 7 and 8 are views illustrating how the actuator of FIGS. 1 -
3 may typically be employed with additional structure to initiate a
desired remote mechanical movement.
Referring to the drawings in more detail and particularly to FIGS.
1 - 3, it will be seen that the actuator basically comprises a
generally cylindrical housing 10 containing a collapsible dual
piston assembly including outer and inner pistons 12 and 15 and a
body portion 14, the assembly being prevented from collapsing by
shear pins 20 and 30. The outer piston 12 is disposed within the
left side of the housing 10 (as veiwed in FIGS. 1 - 3) and has a
reduced cylindrical portion 12a extending from a hole 10a at the
left end of the housing 10 (as viewed in FIGS. 1 - 3) and to which
a biasing force F is applied. The inner piston 15 is disposed
between the outer piston 12 and the body portion 14 and is slidably
moveable within respective aligned axial bores 12b and 14a thereof.
The heat-ignitable shear pins 20 and 30 are disposed in respective
holes 15a and 15b of the inner piston 15 and respective holes 12c
and 14b of the outer piston 12 and the body portion 14 whereby to
maintain the illustrated uncollapsed condition of the piston
assembly against the biasing force F. A threaded sleeve 17 is
threaded into internal threads provided at the right end of the
housing 10 and serves to maintain the uncollapsed dual piston
assembly in a fixed position in the housing 10. The right end of
the housing 10 is sealed by potting material 18 and the left end by
an O-ring 41.
In order to provide for electrical initiation of the actuator
illustrated in FIGS. 1 - 3, each of the heat-ignitable shear pins
20 and 30 has a respective fusible wire 22 or 32 associated
therewith which passes therethrough and extends along the body
portion 14 in recesses 14c (as best shown in FIG. 3) for soldering
to respective ones of lead-in wires 26 and 36 to which initiating
electrical current is applied. As shown, the lead-in wires 26 and
36 are fed into the housing 10 via the threaded sleeve 17 within
which they are potted and are further supported in the housing 10
by respective stress-relieving ferrules 34 disposed in recesses 14d
of the body portion 14. The housing 10, pistons 12 and 15, the body
portion 14 and the threaded sleeve 17 are all of insulative
material in order to prevent shorting of the shear pins 20 and 30
and their associated heat-ignitable wires 22 and 32.
It will be understood from FIGS. 1 - 3 that the actuator may
typically be assembled by first forming a subassembly comprised of
the pistons 12 and 15, the body portion 14, and the heat-ignitable
shear pins 20 and 30 along with their associated heat-ignitable
wires 22 and 32 appropriately soldered to the lead-in wires 26 and
36 carried by ferrules 34. This subassembly is then inserted into
the left end of housing 10 behind the O-ring 41 with the reduced
cylindrical portion 12a extending from the hole 10a at the right
end of the housing 10 and with the lead-in wires 26 and 36
extending from the right side of the housing 10. The threaded
sleeve is then threaded into the right end of the housing 10 and
the potting material 18 then applied. The O-ring 41 together with
the potting material 18 serves to provide satisfactory sealing for
the elements of the subassembly within the housing 10.
Preferably, the heat-ignitable shear pins 20 and 30 and their
associated heat-ignitable wires 22 and 32 are made from a
bimetallic composition which when brought to operating or ignition
temperature will alloy violently and exothermically, resulting in
deflagration without the support of oxygen. Ignition is by heat
alone, requiring only the exposure of the composition to the
operating temperatures. When this reaction is triggered,
temperatures in excess of the boiling point of the constituents are
reached and, once started, the reaction will continue until the
alloying of all available materials to which the reaction is able
to propagate is complete, or unless it is cooled by some mechanical
means below the operating temperature. The reaction products are
normally an alloy of the participating materials. It is important
to note that, although the reaction is violent and very rapid (of
the order of milliseconds), the reaction is not of an explosive
nature and there is no shock or detonation. The only energy
released is thermal (approximate minimum temperature 2,800.degree.
C. - 325 calories per gram and 2,890 calories per cubic
centimeter).
Suitable bimetallic composition which may be used for the
heat-ignitable shear pins 20 and 30 and the heat-ignitable wires 22
and 32 are available from the Pyrofuze Corporation, an affiliate of
Sigmund Cohn Corporation, 121 South Columbus Avenue, Mount Vernon,
New York. The product is sold under the registered trademark
PYROFUZE, is offered mainly as a composite of essentially palladium
and aluminum, and may be purchased in a variety of structural
forms. For the exemplary embodiment of the invention being
described herein, the heat-ignitable shear pins 20 and 30 are
typically formed from 0.001 inch thick PYROFUZE foil containing an
outer shell of palladium and an inner core of aluminum, the
aluminum constituting 99 percent of the composition. The
heat-ignitable wires 22 and 32 are each typically provided as a
composite braid formed by first braiding eight single strands of
0.003 inch diameter PYROFUZE HI- K wire so as to form an inner
braid, and then braiding an additional eight single strands of
0.004 inch diameter PYROFUZE HI- K wire over the inner braid. Each
HI- K PYROFUZE wire used in the braiding has an inner core
containing 0.30 percent silicon (maximum), 0.40 percent iron
(maximum), 0.10 percent copper (maximum), .10 percent zinc
(maximum), 0.05-0.20 percent manganese, 4.5-5.6 percent magnesium,
0.05-0.20 percent chromium, and the balance aluminum, and an outer
shell containing 5 percent ruthenium and the balance palladium.
The above-described foil used for each of the heat-ignitable shear
pins 20 and 30 may typically be about 2.6 inches long and 0.3 inch
wide and is rolled onto its respective heat-ignitable wire 22 or 32
to form a cylinder encircling its respective wire and having an
overall diameter of about 0.07 inch for insertion into its
respective holes 12c and 15a or 15a and 14b, as illustrated in
FIGS. 1 - 3. In order to trigger high speed ignition starting from
a known location, as well as to provide a desired input resistance
for the actuator, it is preferred that one of the soldered
connections between each heat-ignitable wire 22 or 32 and its
respective lead-in wire 26 or 36 be made using only a single one of
the eight strands of the inner braid, as illustrated by numerals
22a and 32a in FIGS. 1 and 2. Of course, care must be taken in
soldering to the heat-ignitable wires to prevent ignition. This is
no problem since heat-ignitable wires of the type described are
able to withstand temperatures up to about 800.degree. F. without
igniting. The overall length of the heat-ignitable wires 22 and 32
may typically be about 1.1 inch and 1.7 inch, respectively, in a
housing 10 which is typically of about 2 inches in length and about
0.5 inch outside diameter. For such an actuator having the typical
heat-ignitable shear pins 20 and 30 and heat-ignitable wires 22 and
32, as described above, it has been found that an input current of
about 7.5 amperes to each pair of lead-in wires 26 and 36 is
sufficient to provide sufficient heating to reliably trigger the
ignition of each of the heat-ignitable wires 22 and 32, starting at
the single strand locations 22a and 33a. The reaction then rapidly
propagates (in a manner somewhat similar to what occurs in a
conventional fuse but much more rapidly) to their respective shear
pins 20 and 30, each of which will then also be ignited as a result
of the heating of the adjacent respective heat-ignitable wire
passing therethrough. The resulting ignition and disintegration of
the heat-ignitable shear pins 20 and 30 removes their restraining
effect on the movement of the pistons 12 and 15 so as to thereby
permit the dual piston assembly to collapse in response to the
applied force F to complete actuation of the actuator, as will next
be considered with reference to FIGS. 4 - 6.
FIG. 4 is essentially the same as FIG. 1 and is provided as a
reference for FIGS. 5 and 6 which illustrate two possible resulting
actuated or collapsed positions of the outer and inner pistons 12
and 15 following ignition of the actuator. It will be noted that,
for greater clarity, neither the shear pins 20 and 30 not their
associated heat-ignitable wires 22 and 32 are shown in FIGS. 5 and
6.
Considering FIG. 5 in more derail, it will be seen that this figure
illustrates the resulting actuated or collapsed position of the
pistons 12 and 15 for the situation where only the shear pin 30 is
ignited, in which case rightward movement of the outer piston 12 by
the distance D is obtained as a result of the right end of the
inner piston 15 moving to the right into the bore 14a of the body
14. FIG. 6 on the other hand illustrates the situation where only
the shear pin 20 is ignited, in which case the same desired
rightward movement of the outer piston 12 by the distance D is
obtained as before, but this time it occurs as a result of the
outer piston 12 moving to the right so that its bore 12b receives a
greater portion of the left end of the inner piston 15.
It should now be evident that, if both of the shear pins 20 and 30
are ignited, which is normally the case, the desired rightward
movement of the outer piston D is again obtained, but in such case
will usually be a result of a combination of the piston movements
illustrated in FIGS. 5 and 6, since both types of movement will be
able to occur. The resulting position of the inner piston 15 will
thus ordinarily be somewhere intermediate that shown in FIGS. 5 and
6, depending primarily on the relative times of ignition of the
shear pins 20 and 30. It will be understood that this resulting
intermediate position of the piston 15 is not significant, since
the important requirement is that the desired rightward movement D
of the reduced cylindrical portion 12a of the outer piston 12 be
achieved in response to the applied force F, and this requirement
will be met as long as at least one of the shear pins 20 and 30 is
ignited. It has been found that with a bias force F of, for
example, eighty pounds applied to an embodiment of an actuator of
the type described herein, only approximately 40 milliseconds is
required following the application of initiating current to the
lead-in wires 26 and 36 for the actuator to reach the fully
actuated condition where the reduced cylindrical portion 12a of the
outer piston 12 has moved the desired distance D.
Having described with reference to FIGS. 1 - 6 the construction and
operation of an exemplary embodiment of an actuator in accordance
with the invention, reference is next directed to FIGS. 7 and 8
which illustrate how such an actuator 50 may typically be provided
within a suitable housing 55 along with other structure for the
purpose of initiating a desired mechanical operation. FIG. 7
illustrates the actuator in its unactuated condition with the
applied force F (FIGS. 1 and 2) being provided by compressed
springs 58 having cooperating members 59 urging a pair of pivotable
latches 62 in respective clockwise and counter clockwise directions
so that they act against the reduced cylindrical portion 12a of the
actuator 50.
FIG. 8 illustrates the actuator 50 in its actuated condition with
the reduced cylindrical portion 12a having moved within the housing
10, and with the latches 62 having been rotated, as indicated by
the arrows A, to free the springs 59 to move in the direction
indicated by the arrows B so as to thereby be able to act on any
suitable structure which might be provided to obtain a resulting
desired mechanical motion.
Although the invention has been described in connection with a
particular exemplary embodiment, it is to be understood that the
construction, arrangement, fabrication and/or use of the invention
is subject to considerable variations and/or modifications without
departing from the scope of the invention as defined in the
appended claims.
* * * * *