U.S. patent number 3,692,264 [Application Number 05/054,461] was granted by the patent office on 1972-09-19 for shock isolation mounts for fragile devices.
This patent grant is currently assigned to Industrial Research Products, Inc.. Invention is credited to Mahlon D. Burkhard, Russell J. Maxwell.
United States Patent |
3,692,264 |
Burkhard , et al. |
September 19, 1972 |
SHOCK ISOLATION MOUNTS FOR FRAGILE DEVICES
Abstract
Shock isolation mounts for miniature microphones, sound
reproducers, and other fragile devices, in which the device is
suspended between thin film support members mounted on a rigid
frame in a configuration such that shock stresses of substantial
magnitude occurring in either direction along a given path are
absorbed almost entirely by tensional stress of one or more of the
film support members. Vibration isolation is also provided,
separately from the shock isolation, by means of one or more
vibration absorption elements, formed of rubber or other material
of high resilience and high compliance in compression, interposed
between the fragile device and support members or between the
support members and the frame or between the frame and an external
support structure. The support members are usually made of plastic,
such as a polyester film, and may be pre-formed to fit the external
configuration of the transducer or other device or may be flat
strips with no pre-forming required.
Inventors: |
Burkhard; Mahlon D. (Hinsdale,
IL), Maxwell; Russell J. (West Dundee, IL) |
Assignee: |
Industrial Research Products,
Inc. (Elk Grove Village, IL)
|
Family
ID: |
21991234 |
Appl.
No.: |
05/054,461 |
Filed: |
July 13, 1970 |
Current U.S.
Class: |
248/621; 206/583;
381/368; 206/588; 968/378 |
Current CPC
Class: |
H04R
1/08 (20130101); G04B 43/002 (20130101); F16F
1/424 (20130101); F16F 2236/022 (20130101) |
Current International
Class: |
F16F
1/42 (20060101); H04R 1/08 (20060101); G04B
43/00 (20060101); G04c 003/00 () |
Field of
Search: |
;248/358R,358A,15,22,26
;179/179,146,180 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Foss; J. Franklin
Claims
We claim:
1. A shock isolation mount for mounting a miniature transducer or
like small, relatively fragile device within a housing, and for
protecting that device against shock damage from excessive
acceleration in either direction along a given path, the minimum
spacing from the device to the housing along that path being a
distance D, comprising:
a first thin, flat film support member, formed of a low-compliance
material having a high modulus of elasticity, extending across one
side of said device approximately normal to said path;
a second thin, flat film support member, formed of a low-compliance
material having a high modulus of elasticity extending across the
other side of said device, said device being wholly supported by
said support members;
each of said support members having a width many times greater than
its thickness;
and rigid frame means, connected to said housing and engaging said
support members in broad area contact, beyond the periphery of said
device, to complete an assembly, the configuration of said frame
means, said support members, and said device being such that
stresses of substantial magnitude produced by acceleration of said
housing and said frame means in either direction along said path
are absorbed primarily by tensional strain, of limited amplitude
less than said distance D, of one of said film support members.
2. A shock isolation mount for a fragile miniature device,
according to claim 1, in which each of said support members is a
flat, flexible strip of plastic film stretched tautly across said
frame means.
3. A shock isolation mount for a fragile miniature device,
according to claim 1, in which said frame means, at the point of
engagement with said film support members, is padded with a
material having high resilience and high compliance in compression
to afford vibration isolation for said device and to preclude
excessive localized stressing of the film under shock
conditions.
4. A shock isolation mount for a fragile miniature device,
according to claim 1, in which at least one vibration absorption
element, of high resilience and high compliance in compression, is
interposed between each of said support members and said
device.
5. A shock isolation mount for a fragile miniature device,
according to claim 1, in which at least one vibration absorption
element of high resilience and high compliance in compression, is
interposed between each of said support members and said frame
means.
6. A shock isolation mount for a fragile miniature device,
according to claim 1, in which each of said thin film support
members is a plastic film having a high modulus of elasticity
pre-formed into a cup-like configuration conforming to one-half of
said device and having a projecting flange engaged by said frame
means.
7. A shock isolation mount for a fragile miniature device,
according to claim 6, in which the outer rim of the cup portion of
each film support member is spaced inwardly of the point of
engagement of that support member with said frame means to allow
limited flexure of that rim and thereby afford vibration isolation
for said device.
8. A shock isolation mount for a fragile miniature device,
according to claim 1, in which said frame means comprises a pair of
rigid mounting members located on opposite sides of said device and
in which the end portions of each of said support members are at
least partially wrapped around said mounting members.
9. A shock isolation mount for a fragile miniature device,
according to claim 8, in which said housing comprises an external
frame for supporting said assembly, and in which at least one
vibration absorption element, of high resilience and high
compliance in compression, is interposed between said external
frame and each of said mounting members to afford vibration
isolation as well as shock isolation for said device.
10. A shock isolation mount for a fragile miniature device,
according to claim 8, in which said housing comprises an external
frame for supporting said assembly, and in which a plurality of
individual rubber vibration absorption elements are interposed
between each of said mounting members and said external frame to
afford vibration isolation as well as shock isolation for said
device.
11. A shock isolation mount for a fragile miniature device,
according to claim 8, in which there are at least three thin film
support members, all of tubular configuration, with said rigidity
mounting members and said device threaded thereinto.
12. A shock isolation mount for a fragile miniature device,
according to claim 11, in which the tubular thin film support
members are separate from each other.
13. A shock isolation mount for a fragile miniature device,
according to claim 11, in which the tubular thin film support
members are all part of a single unitary tube, slit transversely at
spaced points.
14. A shock isolation mount for a fragile miniature device,
according to claim 1, in which said frame means comprises a pair of
rigid ring-like mounting members and in which the peripheral
portions of said support members are clamped between said mounting
members.
15. A shock isolation mount for a fragile miniature device,
according to claim 14, in which said housing comprises an external
frame for supporting said assembly, and in which at least one
vibration absorption element, of high resilience and high
compliance in compression, is interposed between said external
frame and each of said mounting members to afford vibration
isolation as well as shock isolation for said device.
16. A shock isolation mount for a fragile miniature device,
according to claim 14, in which said housing comprises an external
frame for supporting said assembly, and in which a plurality of
individual rubber vibration absorption elements are interposed
between each of said mounting members and said external frame to
afford vibration isolation as well as shock isolation for said
device.
17. A shock isolation mount for a fragile miniature device,
according to claim 14, in which said housing comprises an external
frame slotted to receive said assembly, and in which said support
members project outwardly of said mounting members to isolate said
mounting members from said external frame and to center said
assembly within said external frame.
18. A shock isolation mount for a fragile miniature device,
according to claim 17, in which the outwardly projecting portion of
each of said support members is looped back to afford a
high-compliance vibration absorption element interposed between one
of said mounting members and said external frame to afford
vibration isolation therebetween.
19. A shock isolation mount for a fragile miniature device,
according to claim 14, in which each of said film support members
is bonded to the surfaces of a respective one of said mounting
members.
20. A shock isolation mount for a fragile miniature device,
according to claim 19, in which said film support members are each
bent over a respective mounting member, and further comprising an
external band clamping each support member to its mounting member.
Description
BACKGROUND OF THE INVENTION
This invention relates to new and improved devices for minimizing
the shock forces applied to a miniature transducer or other
relatively fragile device when subject to high acceleration, as may
occur when the device is dropped onto a hard surface or is abruptly
set into motion from a static or rest condition. The invention is
particularly applicable to the protection of the microphones and
sound reproducing units in hearing aids, which may frequently be
subject to relatively high shock stresses; it is also applicable to
the protection of a variety of other electrical, mechanical,
electromechanical, and electronic devices and instruments.
In many applications requiring shock protection for miniature
fragile devices, and particularly in hearing aids, it has been
common practice to surround the devices with rubber, foamed
plastic, or other viscoelastic material. The protective material is
frequently molded into a specific shape to fit the device requiring
protection, or may be assembled from flat stock or bulk material.
The rubber is intended to serve two protective functions. The first
function is to provide vibration isolation for the device with
respect to external structures or with respect to other devices in
a common assembly (e.g., vibration isolation between the microphone
and the sound reproducer in a hearing aid). The second function is
to reduce the shock force applied to the device when the assembly
in which it is incorporated is subject to a severe mechanical
shock. But the conventional rubber or other viscoelastic shock
protection provided for hearing aid transducers and similar devices
is not particularly effective.
The space available for shock isolation elements in modern hearing
aids and like apparatus is quite limited because the apparatus is
by its nature extremely small. Furthermore, the transducers and
other devices requiring protection are usually of miniature
construction and of light weight so that many known types of shock
isolators cannot be used. Moreover, the reduction of shock forces
by compression of rubber or similar viscoelastic material is quite
ineffective as compared to other mechanisms because of the inherent
nature of the stress-strain characteristics of the material itself.
The attempted use of rubber compression elements for simultaneous
shock protection and vibration damping does neither job well - the
resulting structure is usually too stiff for good vibration
suppression and too soft for effective shock protection.
Other compression devices for shock isolation have been proposed,
as, for example, in Weiss U.S. Pat. No. 3,048,668 in which a
hearing aid transducer is suspended within a rigid housing by means
of a plurality of tubular compression members. This type of
compression shock absorber is operationally generally similar to
the rubber shock absorption and vibration suppression elements that
have seen more general use.
There have also been other proposals for vibration isolation and
shock isolation mountings, as few of which have used mounting
members that are stressed at least partly in tension when subjected
to external vibration or shock forces. One such device is shown in
Hoekstra U.S. Pat. No. 2,910,263, in which the shock and vibration
isolation mount for an electronic chassis comprises a suspension
member of braided wire ribbon. Tension stressing of the suspension
ribbon is apparently incidental and flexure of the ribbon is relied
upon for the principal isolation functions. Another device of this
general kind is shown in Lawrence et al. U.S. Pat. No. 3,204,911 in
which vibration damping is effected by a combination of flexure,
compression, and tension of semicircular loops of stranded wire
cable.
Other arrangements in which some tension of the mounting members
has been employed for vibration or shock isolation have utilized
helical springs, as, for example, in Wells U.S. Pat. No. 3,028,138.
But most of these constructions are not readily adaptable to
miniature devices such as hearing aid transducers, requiring
excessive space or exhibiting unduly complex structural
requirements that cannot be readily duplicated on the small scale
required.
SUMMARY OF THE INVENTION
It is an object of the present invention, therefore, to provide
superior shock energy absorbing capabilities in an extremely
limited space in a shock isolation mount for small and relatively
fragile devices.
A further object of the invention is to afford a shock isolation
mount for miniature transducers and the like that not only provides
superior shock protection but which also affords effective
vibration isolation of the device from its surrounding structure. A
specific object of the invention is to provide vibration isolation
in a negligible amount of space in comparison to the space required
for shock protection while at the same time maintaining effective
shock protection.
A particular feature of the invention is the utilization of thin
film support members in a shock isolation mount for miniature
transducers or like fragile devices in which shock stresses are
absorbed by tension of the film to provide the most efficient and
effective use of available space in the overall structure in which
the device is mounted.
Accordingly, the invention is directed to a shock isolation mount
for mounting a miniature transducer or like small, relatively
fragile device within a given limited space and for protecting that
device against shock damage from sudden acceleration in either
direction along a given path. A shock isolation mount constructed
in accordance with the invention comprises a first thin film
support member extending across one side of the device
approximately normal to the path of potential damaging acceleration
and a second thin film support member extending across the opposite
side of the device with the device being wholly supported by the
film support members. Preferably, the support members are formed of
a thin tough plastic film having a high modulus of elasticity. The
film members may be performed to conform to the configuration of
the device to be protected or may be fabricated from flat flexible
strips. The shock isolation mount further comprises rigid frame
means engaging the support members beyond the periphery of the
protected device to complete an assembly, the configuration of the
frame means, the support members, and the device being such that
the energy of shock stresses of substantial magnitude in either
direction along the aforesaid path is absorbed primarily by
tensional stress of at least one of the support members. Energy
absorbed during tensional stress in general includes energy storage
by elastic deformation and energy dissipation by internal loss
mechanisms and by external frictional losses as the support member
slides in response to the tensional stress. In the preferred forms
of the invention, separate vibration isolation is provided by one
or more small vibration absorption elements of rubber or other
material having high resilience and high compliance in compression,
interposed between the fragile device and the support members,
between the support members and the frame means, or between the
frame means and external support structure.
Other and further objects of the present invention will be apparent
from the following description and claims and are illustrated in
the accompanying drawings which, by way of illustration, show
preferred embodiments of the present invention and the principles
thereof and what is now considered to be the best mode contemplated
for applying these principles. Other embodiments of the invention
embodying the same or equivalent principles may be made as desired
by those skilled in the art without departing from the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of a shock isolation mount
constructed in accordance with one embodiment of the present
invention;
FIG. 2 is a perspective view of the shock isolation mount of FIG. 1
as assembled;
FIG. 3 is a sectional elevation view showing the shock isolation
mount of FIGS. 1 and 2 mounted in an external support
structure;
FIGS. 4, 5 and 6 are stress-strain plots showing the operating
characteristics of different forms of shock isolation mounts;
FIG. 7 is a detail sectional view, similar to FIG. 3, illustrating
a modification of the mount construction;
FIG. 8 is a sectional elevation view, similar to FIG. 3,
illustrating another modification of the invention;
FIG. 9 is an exploded perspective view of another form of shock
isolation mount constructed in accordance with the invention;
FIG. 10 is a plan view of the shock isolation mount of FIG. 9 in
assembled condition;
FIG. 11 is a bottom view of the shock isolation mount of FIG. 9 as
assembled;
FIG. 12 is a sectional elevation view taken approximately along
line 12--12 in FIG. 10;
FIG. 13 illustrates a modification of the assembly of FIGS. 9-12 in
a sectional elevation view;
FIG. 14 is a plan view of a further modification of the
invention;
FIG. 15 is a sectional elevation view taken approximately along
line 15--15 in FIG. 14;
FIGS. 16, 17 and 18 are detail sectional views of different forms
of vibration isolators that may be incorporated in shock protection
mounts constructed in accordance with the invention;
FIGS. 19 and 20 are detail views of an alternate construction for
the shock mount of FIGS. 10-12; and
FIG. 21 is a perspective view of another embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates, in an exploded perspective view, a shock
isolation mount 10 constructed in accordance with the present
invention. The shock isolation mount 10 is utilized for mounting a
miniature microphone, sound reproducer, or other small, relatively
fragile device 11 within a limited space and is employed to protect
the device 11 against shock damage from sudden acceleration in
either direction along a given path generally indicated by the
phantom line X. If it is assumed that device 11 is a miniature
microphone or other transducer, it will be recognized that the
device is primarily susceptible to damage as the result of shocks
occurring along the path X, considered as a path perpendicular to
the transducer diaphragm. Shock forces applied to the device in
directions transverse to path X are much less likely to damage the
device. As shown in FIG. 1, the transducer or other miniature
device 11 may be provided with suitable electrical leads 12. The
device is shown as being of rectangular configuration, but the
shock mount 10 can be equally well applied to a device of square,
circular, elliptical or other configuration, as will be apparent
from the detailed description hereinafter.
The shock isolation mount 10 of FIG. 1 comprises a first thin film
support member 13 that extends across one side of the device 11
transversely of the critical shock path X. Member 13 may be formed
from a wide variety of materials but preferably is fabricated from
a thin tough plastic film having a high modulus of elasticity. A
particularly suitable material is polyester film. Member 13 is
preformed to afford a central cup-like portion 14 that conforms to
the configuration of the upper half of transducer 11. That is, when
support member 13 is mounted on transducer 11, the cup-like portion
14 fits closely around the exterior of the upper half of the
transducer. The cup portion 14 of member 13 may be provided with
appropriate apertures 15 for the electrical leads 12 of the
transducer. Moreover, a central aperture 16 may be formed in member
13 to provide access to the transducer 11 for entry or egress of
sound waves.
The shock isolation mount 10 of FIG. 1 further includes a second
thin film support member 17 that is essentially similar in
construction to member 13 and is pre-formed to afford a central
cup-like depression 18 for receiving the bottom half of transducer
11. The shock mount further comprises a rigid frame means that
includes an upper mounting member 19 and a lower mounting member
21. Mounting member 19 is of generally ring-like configuration.
That is, the mounting member is provided with a central aperture 22
that fits around the cup portion 14 of support member 13 when the
mount is assembled (see FIG. 2). Similarly, mounting member 21 has
a central opening 23 for receiving central cup portion 18 of
support member 17.
When the shock isolation mount 10 of FIGS. 1-3 is assembled, the
transducer or other delicate device 11 is deposited in the lower
cup portion 18 of support member 17 and the upper support member 13
is brought down over the transducer with its cup portion 14
encompassing the upper part of the transducer. The two rigid
ring-like mounting members 19 and 21 fit closely around the
projecting cup portions of the support members so that the
peripheral portions of the two support members 13 and 17 are
clamped between the mounting members 19 and 21. This completes the
assembly shown in FIG. 2 and also shown in cross-section in FIG. 3.
It should be noted that the engagement of the rigid frame means
comprising the mounting members 19 and 21 with the periphery of the
support members 13 and 17, and the overall configuration of the
frame means, the support members, and the device 11 are such that
any stresses of substantial magnitude produced by acceleration of
device 11 in either of the opposed directions A and B along the
path X (FIG. 3) can be absorbed only by tensional strain on the
part of one of the support members 13 and 17. It should be
emphasized that the walls of the film cup portions 14 and 18 serve
for tension shock absorption as much as or more than the bases of
the cups. Absorption of such shock stresses by flexure or by
compression of the film support members is minimal.
In order to reach a full realization of the operational advantages
of the shock isolation mount 10, when mounted in a confining
external structure as shown in FIG. 3, some analysis of different
forms of shock isolators is desirable. The fundamental concept upon
which any shock isolator is based is that the energy absorbed by
the compression or extension of the shock isolating elements, plus
the energy lost due to friction forces, must equal energy lost or
gained by the supported device, as the result of stopping of the
device abruptly after dropping some specified height or as the
result of the device being set in motion by an abrupt applied force
of some kind. The energy lost or gained is equal to the area under
the force versus displacement curve of the protected device moving
against the spring system represented by the shock isolation
elements. Mathematically, for the case of a dropped structure, that
energy is
where P is the force created by the abrupt deceleration of the
device, d is the distance the device travels while under the
influence or restraint of the shock isolation mount, and x is the
integration variable. It is evident that a low force P acting over
a long distance d is preferable to a large force acting over a
short distance if low acceleration forces are to be generated and
if a low rate of energy transfer to the protected device is
required. The maximum available distance d (e.g., the rattle space
dimensions D, FIG. 3) is likely to be rather small. Thus, the basic
problem is to produce maximum protection for a fragile device in a
given limited amount of available rattle space D for an anticipated
shock-producing condition by keeping the force generated by the
shock to a minimum level. Some motion of the protected device
relative to the surrounding structure must be provided, but that
motion should be made to occur at reaction force levels critically
designed in relation to the shock resistance characteristics of the
protected device. As the available range of motion is increased,
the reaction force can be made smaller.
For conventional compression shock absorption elements, the
stress-strain or force displacement curve is a tangent curve of the
form generally illustrated in FIG. 4. Rubber and most other spring
elements which compress between the protected device and the
encompassing structure follow tangent elasticity laws. For tangent
elastic elements of this kind, a part of the rattle space D must be
used to contain the compressed elastic material, with the result
that not all of the rattle space can be used for motion of the
protected device.
Furthermore, compression spring members and other tangent
elasticity protectors produce a force increasing with compression
deformation of the spring material. Typically, a rubber compression
material may permit 50 to 60 percent compression at very low force
levels, absorbing only small amounts of energy. If the device is
dropped from a large height, most of the energy must be absorbed at
very high force levels after the rubber is substantially fully
compressed, resulting in large peak accelerations with respect to
the protected device. Thus, tangent elasticity shock protection
elements are inefficient with respect to use of a given amount of
rattle space and in many instances cannot provide the required
protection within existing dimensional limitations.
Improved efficiency in the shock absorption elements is achieved by
utilization of elements which afford linear or generally hyperbolic
deformation characteristics as shown in FIGS. 5 and 6 respectively.
Characteristics of this kind are more readily obtainable using
shock absorption elements that are deformed in tension rather than
in compression. Furthermore, the tension-deforming support members
employed in the present invention make it possible to utilize
virtually all of the available rattle space in motion of the
protected device. That is, tension members such as the support
members 13 and 17, because they usually occupy 5 percent or less of
the total available rattle space, afford substantial advantages in
comparison with compression shock absorption elements because the
latter inevitably require a substantial portion of the available
space for storage of the material when it is compressed.
Preferably, in the shock isolation mount 10 and in the other
embodiments of the invention discussed herein, the dimensions of
the film are selected in proportion to the mass and dimensions of
the protected device and the anticipated maximum shock so that all
of the film is stretched to its elastic limit under maximum shock
conditions.
Referring again to FIGS. 1-3 and the shock isolation mount 10
illustrated therein, it is seen that there are a plurality of
vibration absorption elements 24 on the surface of mounting member
19 opposite that surface of the mounting member which engages
support member 13. The vibration absorption elements 24 may
comprise minute dots of a material having high resilience and high
compliance in compression. A good example is the thixotropic
mixture of silicon rubber known as RTV, which may be applied to the
surface of mounting member 19 by means of a hypodermic syringe or
by transfer techniques such as those used in the "printing" of
various materials onto metal surfaces. A similar series of minute
vibration absorption elements 25 is applied to the lower surface of
the other mounting member 21, as seen in FIG. 3.
In FIG. 3, the shock absorption mount 10 is shown mounted in an
external structure that forms an external frame for the assembly
and that also defines the maximum available rattle space D. This
external frame, forming a part of a housing for the shock
absorption mount, comprises wall members 26, 27 and 28 (one wall
has been cut away) affording a continuous slot 29 for receiving the
edge portions of the shock mount assembly. The film members 13 and
17 project a short distance outwardly of the edges of the mounting
members 19 and 21 into engagement with the side walls of the slot
29 and serve to isolate the rigid mounting members 19 and 21 from
the external frame 26-28. The projection of the film members into
engagement with the walls of the external frame also serves to
center the assembly within the external frame. The vibration
absorption elements 24 and 25, on the other hand, engage the upper
and lower surface of slot 29 to afford vibration isolation for
device 11 with respect to the encompassing structure. The external
frame or housing may be completed by appropriate face plates 31 and
32 which define the limit of maximum displacement of the device 11
along path X and thus determine the maximum available rattle space
D at each side of the device.
If the structure encompassing transducer 11 (e.g., the frame means
19, 21 and housing 26-28 and 31-32 is subject to a high shock force
in the direction indicated by the arrow A, (FIG. 3), transducer 11
tends to remain at rest and the shock force is absorbed almost
entirely by tensional strain or stretching of the side walls of the
cup portion 18 of film support member 17. Conversely, a shock force
in the opposite direction, accelerating the encompassing structure
in the direction of the arrow B, is absorbed by tensional stress of
the side walls of the cup portion 14 of film support member 13.
It is feasible to utilize only the linear range of elongation of
the film support members 13 and 17, as delineated in FIG. 5. On the
other hand, it is equally possible to construct the shock isolation
mount for operation in the non-linear range FIG. illustrated in
Fig. 6, with the film support members absorbing additional energy
of drop or other shock at an approximately constant force level. It
is characteristic of the shock isolation mount that the stresses on
the support members may exceed the range normally considered
permissible for linear springs.
It has been found that polyester films are manufactured and
available in a range of film thickness and with mechanical
constants quite suitable for fabrication of shock isolation mounts
in accordance with the invention. The basic requirements are that
the film have a high modulus of elasticity, that the film be
readily formable, and that the film be capable of a reasonable but
not excessive elongation before exceeding its elastic limit. In
this regard, it should be noted that such highly compliant
materials as rubber are not satisfactory for shock isolation in
mounts constructed in accordance with the invention.
In the mount illustrated in FIGS. 1-3, and particularly in FIG. 3,
vibration isolation is afforded by the highly compliant compression
isolators 24 and 25 and by the flexible extension portions at the
edges of the film support members 13 and 17. Because vibration
forces are of much lower magnitude than the shock forces produced
by dropping or other sudden movement of the device, they can be
effectively damped by the compression elements 24 and 25. Moreover,
it is practical to provide vibration isolation in all directions,
though not necessary in all instances.
FIG. 7 illustrates a modification of the shock mount of FIGS. 1-3.
As in the previous construction, the miniature transducer or other
relatively fragile device 11 is wholly supported between two
pre-formed cup-like film support members 43 and 47 with the edge
portions of the support members clamped between two rigid ring-like
mounting members 49 and 51. Mounting members 49 and 51 correspond
in all respects to the mounting members 19 and 21 of the previous
embodiment except that they are not provided with the vibration
isolation elements employed in the previous embodiment. As before,
the shock mount assembly is mounted in an external frame or housing
illustrated by the wall members 27 and 28 and the cover members 31
and 32, projecting into the slot 29 in the external frame.
In the construction shown in FIG. 7, however, the peripheral
portion 44 of the film support member 43 is looped back over the
adjacent mounting member 49. Similarly, the outer portion 52 of
support member 47 is looped back to the outer surface of mounting
member 51. The two looped portions 44 and 52 of support members 43
and 47 each afford a vibration absorption element of relatively
high compliance effectively interposed between the external frame
and the mounting member with which the support member is
associated. Thus, the looped portions 44 and 52 of the film support
members provide vibration isolation for device 11; they also serve
to center device 11 in the overall construction, including the
external frame.
FIG. 8 illustrated another form of shock isolation mount
constructed in accordance with the present invention. In the
construction shown in FIG. 8, a miniature transducer or similar
fragile device 11 is wholly supported between two film support
members 61 and 62. Support member 61 and 62, like the support
members of the previous embodiments, are pre-formed to afford
cup-like receptacles for the opposite sides of device 11. In this
instance, however, the sides of the cup portions of the support
members flare outwardly away from device 11 instead of conforming
closely to the sides of the device.
The frame means for the construction illustrated in FIG. 8 comprise
a pair of rigid ring-like mounting members 63 and 64 between which
the peripheral portions of support member 61 and 62 are clamped.
Furthermore, the edge portion of support member 61 is bent around
the external surface of mounting member 63. Similarly, the
periphery of support member 62 extends around the outer edge of
mounting ring 64. An external clamp ring 65 fits tightly over the
resulting assembly to afford a strong mechanical connection between
the two film support members and the mounting members 63 and
64.
In the construction shown in FIG. 8, minute individual protruding
spikes or spires 66 of RTV silicon rubber or like material are
spaced around the upper surface of mounting member 63. Similar
elements 67 of the same material are disposed around the lower
surface of mounting member 64. These vibration isolation elements
66 and 67 are interposed between the mounting members and an
external frame or housing generally illustrated in FIG. 8 by the
upper frame member 68 and the lower frame member 69.
The operation of the construction illustrated in FIG. 8 is
generally similar to that discussed above in connection with the
embodiments of FIGS. 1-3 and 7. Low amplitude relatively high
frequency vibrations are effectively absorbed by compression of the
vibration isolation elements 66 and 67. Shock forces along the path
X, on the other hand, are absorbed almost entirely by tension
deformation of either the film support member 61 or the film
support member 62, depending upon the direction in which device 11
is accelerated by the shock. There is some flexure of the film
support members, due to the inclination of the walls of the cup
portions of those members, but this is relatively insignificant and
the principal absorption of shock forces is accomplished, as
before, by tensional strain of the film support members.
FIGS. 9 through 12 illustrate a shock isolation mount 100
constructed in accordance with another embodiment of the invention;
used in conjunction with a rectangular miniature transducer or
other delicate device 111. The device shown has a sound pressure
opening 112 and appropriate electrical leads 113 and 114. The shock
isolation mount 100 includes a rigid frame means comprising two
rigid mounting members 115 and 116. The shock isolation mount
further includes a first thin flat strip film support member 117
and a second film support member that is divided into two segments
118A and 118B.
When assembled, shock isolator mount 100 has the film strip support
member 117 extended upwardly over the outer surface of mounting
member 115, across the top of the mounting member, downwardly along
the inner surface of the mounting member 115, across the space
between the two mounting members, upwardly along the inner surface
of mounting member 116, across the top of member 116, and
downwardly in engagement with the outer surface of mounting member
116, as best shown in FIG. 12.
A similar configuration is employed for the two strips of film 118A
and 118B forming the other support member for this construction
except that these two strips are reversed with respect to strip
117. Thus, strips 118A and 118B each extend across the top surface
121 of device 111 and strip 117 extends across the bottom surface
122 of the device, device 111 being wholly supported by the strip
film support members. The lapped-over portions of the film strip
support members are cemented or otherwise secured to the outer
surface of mounting members 115 and 116. The inner portions of the
film strips are left free of the mounting members so that they can
stretch, in tension, whenever the device 111 is subject to
substantial shock forces along the path X. The space between strips
118A and 118B affords working access to the transducer 111, as
shown by the location of opening 112. It should be noted that the
ends of the transducer are also exposed and readily accessible.
Shock isolation mount 100 functions in essentially the same manner
as described above with respect to the other embodiments of the
invention. Because any shock forces of substantial magnitude are
absorbed almost entirely by tensional strain of the film strip
support members, it is readily possible to achieve a linear or even
hyperbolic stress-strain characteristic as shown in FIGS. 5 and 6.
It will be recognized that mounting members 115 and 116 may
comprise opposed walls of a rectangular cylindrical frame.
Furthermore, although no vibration isolation means or external
housing have been shown for the construction of FIGS. 9-12, it
should be understood that a vibration isolation arrangement like
that shown in the preceding figures can be employed.
FIG. 13 illustrates a slight modification of the shock isolation
mount 100 mounted in an external frame. In the construction shown
in FIG. 13, an external clamping ring 124 is added to assembly 100,
clamping the film strip support members firmly against the outer
walls of the frame members 115 and 116. The edges of clamping rings
124 carry a multiplicity of small vibration absorption elements of
a material having high compliance and resilience in compression.
These elements 122 are engaged by an external frame or housing 123.
It is thus seen that the construction shown in FIG. 13 provides
both vibration isolation and shock isolation for the transducer or
other miniature fragile device 111.
An alternative method of assembly, to afford the same basic
construction as illustrated in FIGS. 9-12, but with the added
advantage of elimination of any need to cement the film support
members to the mounting members, is illustrated in FIGS. 19 and 20.
The shock isolation mount, in this instance, is constructed from a
tube 161 of thin polyester film. The tube is cut at two locations
intermediate its length as indicated by the cuts 162 and 163 in
FIG. 19. The transducer 111 is then threaded into space 166 between
the segments of the film tube, arranged as shown in FIG. 20, and
mounting plates 115 and 116 are inserted into spaces 167 and 168.
The end result is a construction essentially similar to that shown
in FIGS. 11 and 12, with surplus film members 164 and 165 (FIG. 20)
extending directly across the construction. The presence of the
additional film loops 164 and 165 has no detrimental effect.
Indeed, the additional film loops can afford some small vibration
isolation is used to support the transducer along a central line or
at a central portion so that the rigid mounting members 115 and 116
do not contact encompassing structures.
The principal advantage of the construction illustrated in FIGS. 19
and 20 is the elimination of any need for cement or other fastening
of the film supports to the rigid mounting members or to the
protected device. In actual assembly, the mounting members 115 and
116 are inserted first into the tube 161, in spaces 167 and 168,
and then mounted in a jig, following which device 111 is forced
into the central portion 166 of the film tube. A long conical
"needle" is utilized as a guide for threading the transducer or
other device 111 into the desired position. Needless to say, the
dimensions for the elements of the assembly should be selected to
afford a tight fit, tensioning the film slightly, when
assembled.
FIG. 21 illustrates a further modification of the invention that is
essentially similar to the construction discussed above in
connection with FIGS. 19 and 20. The shock protection mount shown
in FIG. 21 utilizes three tubular film support members 171, 172 and
173. The film loops or tubes 171-173 conform to the configuration
realized if the slits 162 and 163 shown in FIG. 19 are extended
completely through the tube 161 of thin polyester film or other
like material. As shown in FIG. 21, each of the tubular film
support members 171-173 is looped around each of the two rigid
mounting members 115 and 116, and the fragile transducer or other
device 111 is mounted between the support members, the tubular
support member 172 being located on the opposite side of device 111
from support members 171 and 173. The overall effect, therefore, is
the positioning of the rigid mounting members 115 and 116 in
successive pockets in the loops corresponding to the pockets 167
and 168 of FIG. 20. The difference is that in the construction of
FIG. 21, the film support members 171-173 may be spaced from each
other, whereas in the construction shown in FIGS. 19 and 20 the
tubular strip segments are contiguous.
FIGS. 14 and 15 illustrate another modification of the present
invention, again using strip film support members that have not
been preformed to the configuration of the transducer or other
device 111 requiring shock protection. In this instance, there are
only two film strip support members 131 and 132, engaging opposite
sides of the device 111.
In the embodiment of FIGS. 14 and 15, the frame means for the
isolation mount comprises a rectangular frame including four
mounting members 133, 134, 135 and 136. The mounting members may
constitute the walls of a rectangular tube. The film strip support
member 131 extends upwardly along the outer surface of mounting
member 136, over the top of the mounting member, downwardly along
the inner surface of mounting member 136, across the bottom surface
of transducer 111, up the inner surface of mounting member 134,
over the top of the mounting member, and downwardly along the outer
surface of mounting member 134. The mounting arrangement for
support member 132 is similar except that it is oriented at an
angle of 90.degree. relative to strip 131, passes over the opposite
side of transducer 111 from strip 131, and is supported from
mounting members 133 and 135. The resulting structure functions in
essentially the same manner for shock absorption as the embodiments
of the invention described above. It will be recognized that an
additional clamp ring (not shown) can be mounted upon the shock
mount of FIGS. 14 and 15, in the manner generally illustrated in
FIG. 13, and that appropriate vibration absorption elements can be
utilized as in the embodiments of the earlier figures.
In all of the embodiments of the shock isolation mount of the
present invention discussed above there is some tendency toward the
development of relatively high stresses at the points at which the
film support members make the transition from one surface to
another in engagement with the mounting members. Referring to FIG.
3, such points of relatively high potential stress are indicated at
the corners 39. In all of the various views, the corresponding
points of potential high stress on the film are shown as having
definite radii; in most instances, the use of a definite radius at
the transition point is sufficient to preserve the integrity of the
film support member.
On the other hand, it may be desirable to form a bead of plastic or
other like material at each such transition point in order to
reduce the concentration of stress as applied to the film support
members. Furthermore, if such a bead is formed from viscoelastic
material affording high compliance for small-amplitude vibrations,
the bead serves a dual purpose, reducing stress concentrations in
the film for shock absorption while at the same time providing
vibration isolation for the transducer or other protected
device.
One construction of this general nature is illustrated in FIG. 16,
in which a mounting member 141 is provided with an edge bead 142
over which a film strip support member 143 extends. A similar
construction, in which a relatively thin layer or pad of highly
compliant vibration isolation material 145 is interposed between a
film strip support member 146 and a mounting member 147 is
illustrated in FIG. 17. FIG. 18, on the other hand, shows the
mounting member 147 and vibration isolation strip 145 used in
conjunction with a film support member 149 of a somewhat different
configuration, allowing a flexure portion 151 in the form of an
overhang over the rim of mounting member 147. These and similar
constructions may be utilized to afford both vibration isolation
and reduction of stress concentration in the shock protection
mount. In any of these constructions, and in the other shock
protection mounts of the invention, vibration isolation can be
aided or even accomplished entirely by interposing resilient
compression isolators between the transducer or other protected
device and the film supports instead of in the external frame or
between the frame and the film supports. Thus, vibration isolation
can be effected by one or more small, compressible, resilient
rubber inserts such as the insert 150 (FIG. 17) between the device
111 and the support strip 146.
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