Note: Descriptions are shown in the official language in which they were submitted.
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SOCKET WITH AUTOMATIC HIGH VOLTAGE CUT-OFF
The invention relates to a safety socket from
which high voltages are removed when the lamp or light
bulb is unscrewed from the socket.
BACKGROUND I THE INVENTION
The invention relates to a socket of the type
adapted to receive a lamp or other load device having a
threaded cylindrical shell serving as one contact, and a
center contact or eyelet serving as the other contact.
Lamp bases of this kind are very common, come in various
lo sizes and are generally referred to as Edison screw
bases, and the sockets therefore are available in
matching sizes. For ordinary domestic sizes of
incandescent lamps, the medium screw base is generally
used, while for industrial applications and high
intensity discharge (HID) lamps, the mogul screw base is
generally used.
When an HID lamp such as a metal halide or a
high pressure sodium discharge lamp is extinguished, the
high vapor pressure in the arc tube prevents immediate
restarting at normal voltage and a cooling interval is
required. This enforced temporary outage may last from
about 1 minute up Jo as much as 15 minutes depending
upon lamp type. Circuits for quickly restarting
extinguished lamps while still hot, commonly referred Jo
as "hot restart circuits," have recently become
LD-~732
z _
available, one such being described in U.S. patent
No. 4,331,905-Owen, Starting and Operating Circuit for
Gaseous Discharge Lamps, issued May 25, 1982. In hot
restart luminaries utilizing such a circuit, the voltage
in the lamp socket on open circuit includes pulses in
the range of 5,000 to 6,000 volts at high frequencies,
for instance at 20,000 ho. Such voltages are hazardous
and a person replacing the lamp when power is on runs
the risk of shock or burn.
SUMMARY OF THE INVENTION
The object of the invention is to eliminate the
hazard presented by high voltages in a screw-type
socket for HID lamps.
So-called safety or shock-proof lamp sockets
for domestic use are well-known. They generally
comprise tabs or shields of insulating material which
block access to the contacts in a socket until forced
aside by insertion of -the lamp base. Such sockets may
prevent finger insertion and are useful for protection
of the careless or of children. But they are ineffective
as protection against voltages of the present magnitude.
Circuit interrupting sockets are also known
for use with fluorescent lamps, particularly instant-
start fluorescent lamps which require relatively
high starting voltages. Such lamps comprise long glass
tubes which are provided with a pair of short-circuited
pins at each end. The interrupting feature is achieved
by completing the ballast primary circuit through the
lamp holder terminals and a pair of short-circuited
pins in the lamp base. This arrangement does not lend
itself to use with the screw-type bases of HID lamps and
their sockets.
Our invention overcomes the problem of high
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voltage hazard in screw sockets by an automatically
operated switch which disables the source of high
voltage. An actuator is incorporated into the socket
and is arranged to operate the switch contacts. When
there is no lamp in the socket the switch is open and
the high voltage source is disabled so that the socket
is hazard-free. As a lamp is screwed into the socket,
the actuator is engaged by the lamp base and causes the
switch contacts to close. This activates the high
voltage source and energizes the socket for normal lamp
operation.
DESCRIPTION OF THE DRAWING
FIGS. lo and lb are closed and open cross
section views in elevation of a socket and
plunger-actuated switch combination embodying the
invention together with the base portion of a lamp and
with a suitable circuit schematically represented.
FIG. 2 is a plan view looking up into tune
socket of FIG. 1 when the lamp is removed.
FIGS. pa and 3b are closed and open cross
section views in elevation of an integral socket switch
variarlt .
FIGS. pa and 4b are closed and open cross
section views in elevation of another socket switch
variant having a side actuator.
DETAILED DESCRIPTION
Referring now Jo the drawing and more
particularly to FIGS. 1 and 2 9 there is shown an
embodiment of the invention which comprises a
cylindrical socket housing 1 of electrically insulating
material such as porcelain or a thermoses plastic. The
housing is open a its bottom end and comprises a
transverse base portion 2 near its top end. In its
central region, base portion 2 is formed with a recessed
generally circular seat and recess 3 for receiving coil
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spring 4. On opposite sides of recess 3, base portion 2
has a pair of slots for receiving the legs pa, 5b of a
U-shaped conductive contact member 5 which has a web
portion underlying coil spring 4. Barbs or punched-out
projections 5c in the legs enrage the topside of base
portion 2 for holding contact member 5 in assembly in
the socket housing with spring 4 pressing resiliently
against the web portion. The legs pa, 5b have elongated
terminal portions or tabs at their ends which project
above the top of the slots for receiving push-on
terminal connectors of known type (not shown).
Fitting within socket housing 1 is conductive
cylindrical screw-threaded metal shell 7 having terminal
strips pa, 7b projecting upwardly from opposite sides.
The arrangement is such that when the terminal strips
are inserted through corresponding slots pa, 8b in base
portion 2, the ends of the strips may be twisted
slightly to engage the topside of base portion 2 and
lock the shell in place within the socket housing. On
its under surface, base portion 2 is formed with
parallel co-planar ledges pa, 9b located inwardly of
slots pa, 8b. As seen in Fig. 1 showing part of an HID
lamp 10 of conventional type mounted in socket housing 1
with its mogul thread base 11 screwed into shell 7,
ledges pa, 9b are so spaced as to engage the shoulder of
the lamp base outwardly of the raised glass web 12
supporting eyelet 13. The ledges thereby serve as stop
means for automatically aligning lamp 10 in the proper
position along the central axis of the socket and thus
provide consistent location of the light center relative
to the optical elements of the luminary. Central
contact member 5, being resiliently mounted in
engagement with oil spring 4, serves in effect as a
"floating" contact which is readily movable in all
directions and accommodates automatically to the
movement of lamp 10 without tendency to tilt or cock the
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lamp at an angle to the socket axis. For further
details on the socket, reference may be made to U.S.
patent No. o'er et at., Electrical Socket,
issued June 17, 1975.
In accordance with the present invention, means
are provided for automatically removing high voltages
from the socket, usually from the central contact
member 5, whenever there is no lamp screwed into the
socket. For this purpose there is provided in the
illustrated embodiment an actuator in the form of a
plunger 14 movable through a vertical passageway in base
portion 2 of the socket. The plunger is biased down-
warmly by a coiled spring 15. The passageway is
located such that the lower end of the plunger is
engaged by the flat shoulder of the lamp base. The
upper end of the plunger engages a blade 16 hinged at
17 on a switch 18, the blade being arranged to actuate the
operating pin 19 of the switch when bent up. If desired,
the conventional micro switch may be used for switch 18
and plunger 14 may be arranged to press directly on the
operating pin 19 of the switch at its upper limit of
travel.
Switch 18 plays the role of a disabling switch
connected in the primary side of the high voltage
pulse source. It is normally open as shown in Fig. lb.
It is closed by upward movement of plunger 14 when a
lamp is screwed fully home into the socket as shown in
Fig. lay As illustrated schematically in Fig. lay the
switch may be connected to interrupt the primary side of
the supply from the line terminals 20 to the high
voltage pulse source or generator 21. In the illustrated
arrangement, the pulse source provides its kilovolt
pulses in series with the secondary side output of
ballast 22 to central contact member 5. Since the
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pulse generator is a low wattage device, this
arrangement has the advantage of requiring only a
relatively low current micro switch to remove the
hazardous kilovolt pulses from the socket. However the
secondary side open-circuit output voltage of ballast Z2
continues to be applied to the socket.
For greater safety it may be desirable to
remove all voltages from the socket whenever the lamp is
removed. Also there are circuits, as disclosed in the
lo previously mentioned Owen patent, in which the pulse
generating circuit is integral with the ballast. In
such ease the disabling switch is inserted in the
primary side of the ballast to interrupt the supply
thereto from the line terminals, and a switch of
adequate current capacity to bear the entire ballast
primary current load is used, as illustrated in Figs. pa
and 3b. In this variant, the switch is an integral part
of the socket assembly. Plunger 14 in this embodiment
is made of a non-conducting material able is stand the
operating temperature of the socket suitable a ceramic
material. A contact 30 topping a metal sleeve 31 is
mounted on the upper end of plunger 14. A conductive
spring blade 32, suitably of phosphor-bronze, is
anchored at 33 to the socket housing and has a forked
end which encompasses sleeve 31 and engages collar 34 in
its lower end. Blade 32 presses plunger 14 down as
shown in Fig. 3b, and causes contact 30 to separate
itself from fixed contact OWE This opens the primary
circuit to the combined ballast and high voltage pulse
generator 36, thereby removing all voltages from the
lamp side of the socket. Screwing lamp 10 home into the
socket forces plunger 14 up and moves contact 30 into
engagement with contact 35 thereby restoring power.
In the variant of the invention illustrated
in Figs. pa and 4b, micro switch 18 is located on the
lo
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side of socket l. Blade 16 of the switch is moved by an
actuator in the form of a spring blade 40 having a fixed
end 41 wedged in a relief in the wall of the socket
housing near the lower end of screw shell 7. The upper
end of actuator 40 normally inclines inwardly and
penetrates into the hollow socket space through a slot
in screw shell 7 as shown in Fig. 4b. When a lamp 10 is
screwed home into the socket, actuator 40 is forced
laterally out by the lamp base as shown in Fig. pa.
This moves the laterally projecting end 42 of the
actuator out through an aperture in the wall of the
housing, causing switch 13 to close the primary circuit
Jo the high voltage generator.
While the present invention has been
described with reference to particular embodiments
utilizing a preferred high quality socket design, it
will be understood that it is equally applicable to
other screw socket designs and that numerous
modifications may be made by those skilled in the art
without departing from the scope of the invention. The
appended claims are in~çnded to cover all such
equivalent variations as come within the true spirit and
scope of the invention.
