Note: Descriptions are shown in the official language in which they were submitted.
ELECTRICAL PLUG WITH LEVER FOR
DISENGAGEMENT FROM A MATING RECEPTACLE
FIELD OF INVENTION
This invention . relates to electrical plugs. It is particularly
S described in relation to low profile electrical plugs for use with AC
convenience
receptacles, but is it not necessarily restricted thereto.
BACkONOUr~D OF INVENTION
Electrical plugs such as those used for connecting to convenience
outlet receptacles typically comprise an insulating body member and a pair of
conductor blades which project forwardly from the bottom face of the body
member. A third conductor may also be used to provide a ground connection.
In one common type of North American plug, the body member is elongated
along the axial direction of the blades, which"permits the body member to be
grasped for removal of the plug from the receptacle. There have been a
number or proposals to provide these plugs with handles to facilitate their
removal from receptacles.
_2_
In another type of plug, the body member has a relatively low
profile which does not permit the body member to be grasped easily for
removal of the plug.
It is old and well known to provide flush-fitting electrical devices
such as fuse holders with a fold flat handle. In U.S. Patent 2,507,092
(Cline),
there is described a low profile electrical plug with a fold flat handle.
The removal of electrical plugs from receptacles may require an
appreciable physical force to be applied through a grasping action, which is
difficult for physically infirm persons.
It is an object of this invention to provide electrical plug devices
which incorporate means to facilitate their removal from receptacles.
It is another object of this invention to provide electrical plugs
wherein the effort required for their removal from a receptacle may be
significantly less than that which is required to pull the plug from the
receptacle.
It is still another object oi~ihis invention to provide electrical plugs
which do not necessitate their being grasped in order to be removed from a
receptacle.
,n
It is yet another object of this invention to provide removal means
of the foregoing type which is particularly adapted for use with low profile
plugs.
In accordance with a broad aspect of this invention, in an
electrical plug comprising a low profile insulating-housing which may
otherwise
be referred to as the body, with at least one conductor blade projecting from
a bottom fac~a thereof for inserting into a receptacle therefor, and a wire
connector exiting the body generally parallel to that bottom face, there is
provided a lever, and pivot means mounting the lever to the body for rotation
about a fulcrum between a first stored position wherein the lever is diposed
within the low profile of the body, and a second position wherein the lever is
upstanding. The lever includes a lever arm having a first end which, when the
lever is disposed in its second position, exterids below the bottom face of
the
housing. Accordingly, the rotation of the lever from its first position to its
second position will, when the plug is in engaged relationship with a
receptacle, cause the first end of the lever arm to bear upon the receptacle
and urge the plug into disengaged relation with the receptacle. It will be
appreciated that the words "bottom face" and "above" as used above and
throughout the specification to describe the plug and its use are used in a
~'~~~1
relative sense to facilitate description, together with the terms "top",
"end", "left"
and "right" rather than in any absolute sense.
Suitably and preferably, the mechanical advantage of the lever is
substantially greater than one, and conveniently may be in the range of about
1.5 to about 10. Also suitably and preferably, the lever will provide a
variable
mechanical advantage, preferably one which decreases as the lever is rotated
from the first position to the second position. In accordance with the
preferred
embodiment the range changes from an initial value of about 5 to a final value
of about 2, but the range may be increased or decreased as desired.
Accordingly, the force necessary to move the lever from its first position
through an initial arc of about i0° may be relatively low. Once the
lever has
been moved through this initial arc, it becomes more accessible so that a
greater force can be applied. At no time does the application of the rotating
force require that the plug or the lever he grasped in any manner, and the
force applied may be restricted to a pushing force, which is usually more
readily applied by physically challenged persons than ~ba pulling force,
particularly where this must be accompanied by a grasping action.
Suitably, the variable mechanical advantage is provided by
shaping the first end of the lever arm as a yam.
~~ ~~~ ~ 9,
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Also suitably, the lever will comprise two lever arms connected
together remote from the first end thereof by a bight, with the lever arms in
parallel relationship. Preferably, the bight includes an outwardly facing
portion
that is upwardly outwardly inclined to facilitate the application of a
rotating
force thereto when the lever is in its first position.
The insulated housing of the plug will normally include a flank wall
which intersects the bottom face about a substantial portion of the periphery
thereof. Suitably and preferably, the lever arms and the bight when in the
stored position will be contiguous with the flank wall along substantially the
whole of the length of the lever. Desirably, the lever and the flank wall will
be
provided with co-operating means which prevent the rotation of the lever
beyond its first position.
Preferably, the lever arms are attached to the insulating body by
gudgeon pins integrally formed with the lever arms, which rotate in gudgeon
openings provided in the body. In accordance with the preferred embodiment,
the gudgeon pins and openings have a complementary shape serving to
capture the gudgeon pins and prevent their withdrawal from the gudgeon
openi~~gs along the axis thereof.
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~'he most commonly adopted receptacles for domestic use in
North America are formed as duplex pairs, with a standard modular interval
between the outlets of approximately 38.20 mm. (1.50 in.), and it is a common
expedient to ensure that a plug inserted into one outlet of the receptacle
will
not intertere with a plug in the adjacent outlet. With low profile plugs
wherein
the wire cord will normally exit from the plug body along an axis in a plane
parallel to the face of the plug, the angle subtended by the axis within this
plane will be selected so that the wire cord does not form an impediment to an
adjacent outlet.'~Suitably, this angle will be not greater than about
60° relative
to an axis passing through the conductor blades of the plug. In the instant
lever- off plugs, the operation of the lever of one plug must not be
significantly
impeded by the adjacent plug. Generally speaking, this condition will be
ensured where the fulcrum of the lever subtends an angle within the range of
about 90° to about 45° with the axis passing through the
conductor blades, with
90° being preferred. In accordance with the preferred embodiment
wherein the
lever comprises a pair of lever arms interconnected by a bight, the lever has
an outwardly facing flank which extends over a circular arc of about
230°, the
diameter of which arc is marginally less than the modular spacing of the
duplex outlets, and the axes of the wire cord and of the fulcrum may be varied
within the above limits without conflict.
The foregoing objects and aspects of the invention, together with
other objects, aspects and advantages thereof will be more apparent from a
consideration of the following description of the preferred embodiment thereof
taken in conjunction with the drawings annexed hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
In the Drawings-
FIG. 1 Shows a plug in accordance with the
invention in perspective view from the
top, front, right side;
FIG.2 Shows the plug of FIG. 1 in top
elevation;
FIG. 3 Shows the plug of FIG. i in bottom
elevation;
_g_
FIG. 4 Shows the plug of FIG 1 in right side
elevation;
FIG.5 Shows the plug of FIG. 1 in front
elevation;
FIG. 6 Shows the body of the plug of FIG. 1 in
right side elevation before assembly
with the lever;
FIG. ' Shows the lever of the plug of FIG. 1 in
bottom elevation befiore assembly with
the plug body; and
FIGS. 8 - 10 Show in schematic form, the plug of
FIG.1 in assembled relationship with a
receptacle and the progressive action
of the lever in the removal of the plug
from the receptacle, with hidden detail
2~~8~1'9
shown in dashed outline.
FIG. 11 Shows a pair of plugs engaged in a
duplex receptacle which is shown in
dashed outline;
FIGS 12 - 13 Are similar to FIG. 3, but show different
embodiments of the plug.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings Iri detail, a plug in accordance with
the invention is identified generally therein by the numeral 10. Plug 10
comprises an insulating body 12 having a bottom face 14, a top face 16 and
a flank wall i8 extending therebetween. A pair of conductor blades 20, 22
project downwardly from bottom face 14, and a wire cord conductor 24 extends
from body 12 and attaches thereto over rearward portions of flank wall 18 by
means of a strain relief 26; the conductor wires of cord 24 connect to
conductor
blades 20, 22 within body 12 in a conventional manner which is not
illustrated.
Conductor blades 20, 22 have a transverse axis 32 passing therethrough, and
~~~~g~9
- 10-
wire cord conductor 24 exits from body 12 along an axis 34 which extends in
a plane parallel to the plane of bottom face 14.
Plug 10 further comprises a lever 40 which includes a pair of
mirror image lever arms 42 interconnected by a bight 44. A gudgeon pin 46
extends from each of lever arms 42 in opposed relationship. Gudgeon pins 46
include at the distal end thereof, a head portion 50 of enlarged diameter. A
pair of circular gudgeon openings 52 are formed in body 12 on a notional axis
54 which is disposed intermediate blades 20, 22 within body 12, adjacent the
centre of resistance of engagement of the plug with a receptacle as will be
referred to subsequently at greater length. Gudgeon openings 52
communicate with flank wall 18 and are respectively intersected by a pair of
T shaped slots 56, which also intersect bottom face 14. Lever 40 is assembled
onto body 12 by urging gudgeon pins 46 along slots 56 until the gudgeon pins
snap in to the gudgeon openings 52, so that notional axis 54 then defines a
fulcrum 60 of the lever 40.
LEVer 40 is rotatable about fulcrum 60 between a first stored,
position, as seen in FIGS. 1 - 5, wherein the lever does not project below the
plane of bottom face 14, and a second position, as seen in FIG. 10, wherein
the rearward end 70 of the lever projects below the bottom face.
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The over-rotation of lever 40 beyond the first position is precluded
by providing the forward end portion 72 of flank 18 with an upwardly rearward
inclination, which will form an abutment for a similarly inclined portion 74
on the
inwardly facing wall surface' of bight 44. The bottom surtace of bight 44 is
upwardly forwardly inclined at 76 to facilitate the application of a force F
to
lever 40 when it is desired to remove plug 10 from engagement with a
receptacle R. As best considered with reference to FIGS. 8 -10, a receptacle
R has electrical contacts C with a gripping portion disposed at a distance D
below the upper surface S of the receptacle. The plug 10 has conductor
blades 20, 22 with a length L. Typically L is about 17 mm and D is not less
than about 50% of L. Accordingly, the blades 20, 22 may be inserted a
distance of about 9 mm into the receptacle R before any significant resistance
is encountered, and the length of the blades engaged by contacts C is
approximately 8 mm. As a corollary of this, the withdrawal of plug 10 from its
fully seated position in receptacle R by a distance of L - D equal to about 8
mm will disengage the blades 20, 22 from the grip of contacts C, and will
k
permit the further withdrawal of the plug from the receptacle without any
substantial resistance. Desirably, lever 40 will be dimensioned such that when
in its second position, the lever end will project a distance of about 50% of
the
- 12-
length L of blades 20, 22, or about 8 mm in this exemplary embodiment. Lever
40 is provided with a cam surface 80 which is arranged to progressively
decrease the mechanical advantage of the lever with the degree of rotation
thereof from the first position to the second position. The effect of this is
to
minimize the force F that is necessary to rotate lever 40 when the lever is at
or adjacent its first position, wherein it will be generally flush with the
surtace
S of receptacle R and less readily accessible than when it is more upstanding
from the receptacle R and the body 12 of plug 10. Suitably, for a plug 10 for
use with a standard North American 15 amp receptacle, the mechanical
advantage will change in the range of about 5:1 to about 2:1. Experimentally,
the force F applied to the forward extremity of lever 40 in a tangential
direction
to the motion of the lever was determined to be about 2.25N adjacent the first
position of the lever, and this increased to about ~S.SN adjacent the second
position. This contrasts with a force of about i1N which was required to be
applied along the axial direction of insertion of blades 20, 22 to release the
blades of plug 1n~ from engagement with the contacts C of receptacle R.
Lever 40 has an outwardly facing flank 80 which describes a
circular arc extending over an angular interval of approximately 260°,
and has
a diameter d equal to 36.60 mm. (1.44 in.), which is somewhat less than the
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intermodular spacing of 38.20 mm. (1.50 in.~ between two outlets O of a duplex
pair of receptacles P shown in FIG. i l, whereby the body 12 of one plug 10
engaged in one outlet will not interfere with the body of another plug engaged
in the adjacent outlet irrespective of the angular rotation of the plug body
with
respect to the duplex outlet. This angular rotation will of course be set by
the
axis 32 of conductor blades 20, 22. The axis of fulcrum 60, being at right
angles to blade axis 32, will ensure that the inclined surface 76 of lever 40
through which the force F is applied to rotate the lever, is not impeded, and
the
axis 34 of wire cord 24 and strain relief 26, being collinear with the blade
axis
32, will ensure that the wire cord will not intertere with a plug 10 engaged
in an
adjacent outlet O of the duplex pair P.
The inter-relationships of the blade axis 32, wire cord axis 34 and
of the fulcrum 60 may be changed, however, while avoiding inter-plug
interference. Thus, with reference to FIG. 12, the blade axis 132 of a plug i
10
is intersected at an angle of approximately 45° by the fulcrum 160 and
by the
wire cord/strain relief axis 134, and with reference to FIG. 13 the blade axis
of
a plug 210 is intersected by the fulcrum 260 at an angle of 90° and by
the
wire/corc~ strain relief at an angle of about 45°. In this last
embodiment a
ground pin 282 is also provided, although it will be appreciated that a
similar
- 14-
V
ground pin could have been provided if desired in each of the embodiments.
The foregoing embodiments are illustrative only of the invention
and not limitative thereof. It will be appreciated that many other variations
may
be made, some of which may be preferred according to particular
circumstances, and it is intended that all changes be encompassed by the
Claims appended hereto.
