Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the connection between an
electrical device and an insulated cable or cord or, more
particularly, to lamp and cord construction in integral
string sets.
In the past, a variety of constructions have been
used to electrically connect an electrical device, e.g., a
lamp or socket, to a cable or power cord. Considering prior
art decorative strirg sets as one, but not the only
example, the lamp is connected to the cord by way of a
socket. The socket generally comprises conductive tabs
which are crimped, twisted, soldered, or welded to the stripped
ends of the wires in the cord. The stripping, crimping, etc. all
involve complex assembly procedures which add to the cost of
the string set. Further, however, reliably the socket is
connected, a lamp must be inserted and make good contact
with the socket, a condition not necessarily obtained in the
hands of the consumer. Also, the string set must be
mechanically strong at the connections to withstand handling,
particularly the stress due to pulling in the direction of
the wire.
If the string set is intended for outdoor use, the
connections must be further protected from the environment
to avoid deterioration of the connections or possible short
circuits due to moisture. In the prior art, string sets
designated as suitable for outdoor use are noticeably heavier
in construction and generally costlier to make. Further,
whatever the recommendations of the manufacturer, there is
a problem in that some consumers will use an indoor set
outdoors, despite the attendant risks.
In view of the foregoing, it is therefore an object
of the present invention to provide an improved connection
between an electrical device and insulated wire.
Another object of the present invention is to
provide a superior integral string set.
A further object of the present invention is to
provide a string set suitable for use either indoors or
outdoors.
Another object of the present invention is to
provide a mechanically strong string set.
A further object of the present invention is to
simplify the construction of integral string sets.
The foregoing objects are achieved in the present
f 10 invention wherein the lead wires from each lamp are mechanically
clamped to the wires ina power cord by a plastic sandwich
which is thermally or ultrasonically softened temporarily. -~
In one embodiment of the present invention, the insulation
is not removed from the free ends of the power cord to which
the lamp is joined. In another embodiment, the insulation
is removed.
A more complete understanding of the present
invention can be obtained by considering the following
detailed description in conjunction with the accompanying
drawings, in which:
FIGURE 1 illustrates a partially assembled lamp and
wire sandwich.
FIGURE 2 illustrates a bottom view of the assembled
sandwich prior to softening the plastic.
FIGURE 3 illustrates the sandwich after softening.
FIGU~E 4 illustrates an integral string set in
accordance with the present invention.
FIGURE 1 illustrates a side view of a preferred
embodiment of the present invention as used in fastening wire
lamps to the wire of a string set. Specifically, a series
connected string set as used for decorative lighting during
holidays may be considered as a plurality of lamps interconnected
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by a plurality of wire segments, the lamps and segments
together combining to form the series circuit which is
connected to a plug. In FIGURE 1, wire lamp 11, that is,
a lamp having lead wires extending from the sealed end -
thereof but lacking any base or base structure, is connected
to insulated wire segments 12 and 13 by way of lead wires 14
and 15. In a preferred embodiment of the present invention
lead wires 14 and 15 are doubled back on themselves to
increase the number of contacts with segments 12 and 13. It is
also preferred, although not necessary for the present
invention, that segments 12 and 13 comprise what is knowrl as
stranded wire, i.e. a plurality of strands of wire twisted
together as opposed to a single solid conductor. Wire segments
12 and 13 are interconnected by lead wires 14 and 15 and
filament 16. Also illustrated in the embodiment of
FIGURE 1 iS a shunt 17 such as disclosed in Canadian
application Serial No.3~ , filed concurrently herewith
and assigned to the assignee of the present invention.
Shunt 17 provides the dual functions of supporting and
positioning lead wires 14 and 15 within lamp 11 as well
as continuing the circuit in the event filament 16 opens.
Located from behind segments 12 and 13 is a plastic
sheet 18 which encloses the contact area between segments 12
and 13 and lead wires 14 and 15 respectively. The function
of plastic sheet 18 can be better understood by considering
FIGURES 2 and 3 which comprise end views of a preferred
embodiment of the present invention, before and after sealing
respectively.
As illustrated in FIGURE 2, overlying the other side
of a contact area is a second plastic sheet 19 of the same
general proportions as sheet 18 and approximately parallel
thereto. Lead wires 14 and 15 respectively touch conductors
21 and 22 from segments 12 and 13. The lead wires are not
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soldered, welded, or otherwise electrically bonded to
conductors 21 and 22. In assembling a string set in
accordance with the present invention, plastic sheets 18 and
19 are deformed, e.g. by thermal or ultrasonic means, to bond
to each other and the insulation on segments 12 and 13,
thereby sealing the region of contact between lead wires
14 and 15 and wires 21 and 22 respectively.
Unlike prior art contacts formed in deformed
plastic, it has been found that one conductor, e.g. wire 14,
need not rest on an anvil for the other conductor, e.g. lead
wire 12, to make reliable contact therewith. During the
bonding or deformation, the conductors are surrounded by
plastic in a liquid state and, upon cooling, are brought
into electrical contact. As should be apparent, this simplifies
manufacture since an exposed conductor does not have to be
covered in subsequent operations: a totally enclosed,
mechanically and electrically secure connection is made in
a single operation.
While illustrated for the sake of clarity in
FIGURES 1 and 2 as having the ends thereof stripped, wire
segments 12 and 13 preferably comprise a core conductor
surrounded over its entire length by an insulating jacket. It
has been found that during the deformation this insulation
does not interfere with the contact between lead wires 1~ and
15 and conductors 21 and 22. It appears that the lead wires
simply penetrate through the plastic in the fluid state and
make mechanical contact with the conductors. In this
manner, the construction of string sets in accordance with
the present invention is even more simplified, requiring
only the severance of the insulated wire into segments.
As illustrated in FIGURE 3, the deformation of
sheets 18 and 19 causes the plastic, which may comprise any
suitable thermoplastic such as polyvinylchloride (PVC), to
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flow into the regions and force lead wires 14 and 15 into
mechanical contact with wires 21 and 22 respectively. It
; is a characteristic of most thermoplastics that upon going
from the liquid state to the solid state, some shrinkage
occurs. This shrinkage causes a continuous pressure to be
applied to the contact thereby assuring a reliable
electrical connection despite the absence of solder or welds.
Further, since the plastic sheets are bonded to each other as
well as to the plastic insulation around segments 12 and 13, the
entire contact area is sealed against hostile environments
as well as being mechanically strong, as strong as wire
segments 12 and 13 themselves.
FIG~RE 4 illustrates a string set in accordance
with the present invention wherein a plug 31 has connected
thereto a plurality of wire segments, such as segments 33
and 34 which in turn are interconnected by a plurality of
lamps 11. Surrounding lamps 11 are ornamental structures
such as disclosed in Canadian application Serial No. 3 ~ P,J~G
filed concurrently herewith and assigned to the assignee of
the present invention. As described in that application,
ornamental structures 35 preferably comprise a unitary
plastic part haviny tabs on the lower portion thereof which
fit around the contact area of the lamp as well as a portion
of the wire segment connected thereto. In accordance with the
present invention, these tabs may be substituted for plastic
sheets 18 and 19 or may be provided in addition to plastic
sheets 18 and 19 and further sealed to each other and to the
insulation of the wire segments. In the latter form, the
connections between the wire segments and lamps 11 are thus
doubly sealed against the environment, thereby providing a
lightweight, easily constructed string set which may be
used either indoors or outdoors.
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Having thus described the invention it will be
apparent to those of ordinary skill in the art that various
modifications can be made within the spirit and scope of the
present invention. For example, the choice of a particular
thermoplastic depends on considerations external to the
present invention, e.g. cost and government regulations.
Further, while illustrated as connected to segmented wire,
wire lamps may also be connected across continuous, parallel
conductors in accordance with the present invention. For
this connection, the thermal or ultrasonic source is suitably
shaped to contact the sheets at the appropriate locations.
The resultant string set then comprises parallel connections -
of the lamps.
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