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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to cabinet assemblies for housing electronic
apparatus or the like and, more particularly, to such cabinet assemblies
and methods for forming the assemblies which are characterized by high
integrity radio frequency interference seals and improved structural
strength.
Electronic equipment of various sorts is frequently assembled in a modular
form wherein a typically box-like cabinet assembly is constructed for
receiving one or more individual electronic sub-assemblies. The cabinet
assemblies may, in turn, be housed within a larger chassis or may be
utilized in a stand-along mode. In either case, the electronic
sub-assemblies are often contained on printed circuit boards which include
suitable mounting apparatus enabling the boards to be easily inserted or
removed from the cabinet assemblies as the need arises. This modular
arrangement facilitates logistical operations associated with maintaining
the equipment in that, for example, repair operations, including stock
piling of spare parts, may be performed on a sub-assembly basis by
relatively inexperienced maintenance personnel in a minimum period of
time. These latter considerations largely account for the recent
popularity of such modularized electronic equipment.
Due to the nature of electronic equipment, and especially particular
apparatus such as radio receivers and transmitters, the cabinet assemblies
preferably supply an operational environment secure from radio frequency
interference (RFI). If allowed to exceed certain levels, radio frequency
interference permeating the cabinet assembly from an external source can
seriously degrade the performance of the electronic sub-assemblies by
subjecting them to excessive levels of noise. On the other hand, radiation
of radio frequency interference from within the cabinet assembly can
adversely affect the performance of other nearby equipment. To avoid these
problems, most military agencies, for example, provide strict
specifications defining precise limits of radio frequency interference to
which various types of equipment may be subjected as well as to maximum
permissible levels of radiation.
One technique commonly used to decrease the radio frequency interference
susceptibility of cabinet assemblies adapted for housing electronic
apparatus is to secure the various joints of the cabinets with special
radio frequency interference shielding materials. These shielding
materials, an exemplary form of which may comprise a strip of silicone
rubber impregnated with wire fibers or the like, are normally glued to one
or more surfaces of the cabinet assembly to seal the joints for preventing
externally generated radio frequency interference from exposing and
interfering with the electronic equipment contained within the cabinet and
for preventing internally generated radio frequency interference from
radiating outwardly from the cabinet. While such prior art efforts have
been successful to a degree, they have not always reduced radio frequency
interference leakage to an acceptable level in a manner which is
conveniently and cost effectively implemented.
In addition to providing adequate radio frequency interference shielding,
the cabinet assembly is also preferably relatively light-weight and
inexpensively manufacturable while, at the same time, possessing adequate
structural strength. These requirement have heretofore been considered to
be somewhat conflicting and have not been fully satisfied by any known
prior art cabinet assembly useful for housing electronic apparatus.
SUMMARY OF THE INVENTION
In view of the foregoing, it is a basic object of the invention to provide
a new and useful cabinet assembly for housing electronic sub-assemblies.
It is a further object of the invention to provide such a cabinet assembly
which is characterized by high integrity radio frequency interference
seals.
Yet another object of the invention is to provide a cabinet assembly of the
foregoing type which is conveniently and inexpensively manufactured and
which is relatively light-weight and yet possesses a high degree of
structural strength.
In accordance with these and other useful objects, the cabinet assembly of
the present invention comprises an extrusion having a pair of opposed
upstanding side walls and an upstanding end wall extending transversely
between the side walls. A deck member is secured between the side and end
walls near the bottom of the extrusion for supporting an item of
electronic apparatus. A lid member is provided for enclosing the open top
end of the extrusion and is characterized by a configuration substantially
conforming to but slightly smaller than the dimensions thereof. A mounting
rail comprising a transverse flange formed integrally with the extrusion
extends interiorally about the side and end walls near the top end of the
extrusion and is adapted for supporting the lid member. Finally, a
flexible radio frequency interference sealing material is disposed
overlying the mounting rail.
In the assembly of the cabinet, the lid member is forced into compression
against the mounting rail and sealing material leaving a slight
intersticial area between the surfaces of the side and end walls and the
lid member. The radio frequency inteference sealing material is forced
upwards from the intersticial area and may slightly overlay portions of
the top surface of the lid member as well as portions of the exterior
surfaces of the end and side walls. The seals thereby formed provide a
high degree of radio frequency interference integrity wherein radiation
must follow a rather tortuous path to be either radiated from or into the
cabinet assembly through the joints thereof. A similar lid member may also
be used to secure the bottom end of the extrusion.
The deck member is characterized by a double bend configuration at its
front edge which, together with the extrusion, form a structurally sound
configuration while utilizing a minimum degree of metal thereby reducing
the weight of the assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view, partly in exploded form, showing the cabinet
assembly of the present invention.
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1.
FIG. 3 is an enlarged view of a portion of the cross-sectional view shown
in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and in particular, to FIG. 1, the cabinet
assembly of the invention, identified generally by reference numeral 10,
comprises a one-piece generally U-shaped extrusion 12 having a pair of
opposed upstanding side walls 14 and 16 and a transversely extending end
wall 18. A deck member 20 is disposed between the side and end walls 14,
16 and 18 and adapted for supporting an electronic sub-assembly within
cabinet assembly 10. The deck member 20 includes three upstanding flanges
24 each abutting one of the walls 14, 16, and 18. Conventional means such
as screws 22 or the like secure deck member 20 within cabinet assembly 10
by appropriately fastening each of the flanges 24 to its respective wall
14, 16 and 18 to provide increased stress distribution between the
members. Also, good thermal contact is thereby established between the
members which facilitates heat dissipation throughout the assembly. The
front-most edge 26 of deck member 20 is formed having a double bend adding
structural strength to the deck without utilizing additional metal. A pair
of tabs 28 extend from the distal ends of front edge 26 in abutment with
side walls 14 and 16. Screws 22 fasten tabs 28 to the side walls as
previously described.
A mounting rail or flange 30, comprising a portion of the extrusion making
up side and end walls 14, 16 and 18, extends transversely from and
interiorally of the side and end walls 14, 16 and 18. Mounting rail 30,
which is disposed slightly below the upper end of cabinet assembly 10,
thusly extends completely about the interior surfaces of walls 14, 16 and
18 forming a generally U-shaped interior mounting structure. A similar
mounting rail 32 is disposed slightly above the bottom end of assembly 10
forming a second U-shaped interior mounting structure.
Referring now to FIG. 2, a flexible radio frequency interference sealing
material 34 is disposed completely overlying the entire extent of mounting
rail 30. Sealing material 34 may comprise, for example, a strip of
silicone rubber impregnated with wire fiber. Such material is well-known
in the industry and may be obtained from various sources.
The top end of the assembly 10 is closed by a generally flat lid member 36
which has a configuration substantially conforming to the shape of the top
end of assembly 10. The dimensions of lid member 36, however, are slightly
less than the corresponding dimensions of the top end of assembly 20 such
that when the lid member is seated on mounting rail 30 a small
intersticial area is formed between the lid and the interior side surfaces
of the side and end walls 14, 16 and 18. It will be noted that this
intersticial area leaves exposed a small portion of the sealing material
34 disposed over mounting rail 30. Upon forcing lid member 36 into
compression with mounting rail 30, the sealing material is forced upward
from the intersticial area forming a narrow layer partly overlying the top
surface of lid member 36 and the outside surfaces of walls 14, 16 and 18.
The sealing material 34, under compression from lid member 36, digs into
the metallic members forming an electrical bond which, in association with
the labyrinth type seal, forms a highly stable and secure radio frequency
interference seal. In particular, electro-magnetic radiations eminating
from the interior of cabinet assembly 10 must pass along a path making at
least two right angles before radiating from the joint formed between lid
member 36 and extrusion 12. Similarly, electromagnetic radiations
eminating from outside cabinet assembly 10 must follow a path including at
least two right angles in order to penetrate this seal.
Lid member 36 may be secured to extrusion 12 by means of suitable screws 38
passing through aligned apertures 39 in the lid and in the mounting rail
30. When so secured, the lid member 36 serves as a stress bearing member
and also functions as a dust cover and provides electro-status shielding
for the electronic equipment disposed within the cabinet assembly 10.
A bottom plate 40, constructed identically with lid member 36, is secured
to bottom mounting rail or flange 32 in a manner identical to that
previously described with respect to the lid member. FIG. 3 shows an
enlarged view of the seal formed by the material 34. It will be observed
that the sealing material 34 is disposed between mounting rail 32 and
bottom plate 40, extends downwardly from the intersticial area between the
walls 14, 16 and 18 and bottom plate 40 and then partially overlies a
portion of the bottom surface of bottom plate 40 and a portion of the
outer surface of the extrusion walls.
Referring back to FIG. 1, a front panel 42 is secured across the opened
front end of extrusion 12 and serves as a stress bearing member which adds
structural strength to the assembly 10.
While a particular embodiment of the invention has been shown and
described, it will be obvious to those skilled in the art that changes and
modifications may be made without departing from the invention in its
broader aspects. For example, various other sealing materials may be used
in place of the wire fiber impregnated silicone rubber described above.
Therefore, the aim in the appended claims is to cover all such changes and
modifications as fall within the true spirit and scope of the invention.
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