Note: Descriptions are shown in the official language in which they were submitted.
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Variou3 means are known to sequentially fire a photo-
flash lamp array utilizing a circuit board having the
firing circuitry deposited directly thereon. The use of
radiation-sensitive switches and fuses connected in said
circuitry is also known. A photoflash unit of this general
type is described in Uni-ted States Patent No. 3,89~,226
dated July 8, 1975, to James M. Hanson, wherein the parti-
cular flash lamps employed provide an open circuit condition
between the lead-in wires upon flashing and radiation-
sensitive switches permi-t the next lamp to be flashed. It
is also recognized in U.S. Patent 3,532,931 dated October
6, 1970, to P.T. Cote et al, that fuse means are useful
when the flash lamps are not reliably non-shorting upon
flashing to assure that an open circuit condition will result.
By such means, an already fired flash lamp exhibiting re-
latively low resistance between the current conductors by
` reason of a shorted condition cannot thereafter absorb part
of the electrical energy when the next firing pulse is applied
to the next flash lamp and thereby possibly preclude the de-
sired firing sequence from taking place.
It is a primary object of the present invention to provide
fuse elements deposited on a circuit board to enable as-
sociated flash lamps to be fired in sequence.
Another important object of the invention is to provide
a circuit board of this type having both radiation sensitive
switching elements and radiation sensitive fuse elements de-
posited on the circuit pattern for cooperative therebetween
when the associated lamps are flashed.
A still further object of the present invention is to
provide fuse means which interrupts the circuit path by
thermally melting or decomposing -the underlying substrate
to create a hole or opening for permanent disruption of the
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electrical connection.
These and other objects of the present invention are
achieved with a lamp firing circuit pattern which includes
radiation sensitive switches when radiation sensitive fuse
elements are deposited on said circuit pattern to physi-
cally interrupt the circuit path upon activation. Fuse
elements operating in -the desired manner can be obtained
by simp]y depositing a mass of adherent radiation absorbing
material on the cixcuit pattern itself at a location suf-
ficiently proximate to the associated flash lamp so as tobe actuated by the emitted radiation for permanent dis-
ruption of the electrical connection to the actuating flash
lamp. Suitable radiation sensitive switches providing
the desired cooperation of sequential lamp firing are de-
scribed in United States Patent No. 3,990,833 dated
November 9, 1976, to Fred F. Holub et al, and also assigned
to the assignee of the present invention so as not to
` require repeated description in the present application.
, Generally, said switches are also deposited on the circuit
pattern for actuation by radiation being emitted from
ad]acent flash lamps to provide a circuit path to -the next
flash lamp to be fired by undergoing conversion from a high
electrical resistance to a low resistance state.
For satisfactory operation in a photoflash unit of
this type utilizing radiation sensitive switches as dis-
closed in the above referenced U.S. 3,990,833 dated
November 9, 1976, it is required that the fuse elements
exhibit a relatively low electrical resistance up to
approximately 1,000 ohms before actuation but exhibit an
electrical resistance across the interrupter circuit path
after actuation of at least 108 ohms. Understandably, the
heat absorption capability of the fuse element is an ad-
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; ditional consideration and such radiation absorbent particu-
late solids as carbon, copper oxide, and stannous oxide
provide both essential requirements. A simple suspension
of the radiation absorbent material in an organic polymer
binder can be deposited on the circuit pattern with the
desired operating characteristics being further dependet
on cross-sectional geometry, color, and thermal properties
that can be still further modifiered with fillers all in
a known manner.
lOFIG. l is an illustration of an otherwise known
multiple flash lamp circuit board having a lamp firing
circuit pattern deposited on a dielectric substrate and
radiation sensitive switching devices connected in said
circuitry for sequential firing of a plurality of flash
lamps connected thereto which has been modified in ac-
cordance with the present invention; and
FIG. 2 iS an electrical schematic diagram illustrating
the circuit path for one group of four flash lamps being
sequentially fired by the circuit board configuration in -
FIG. l.
In the preferred circuit board embodiment depicted
in FIG. l, both radiation sensitive switches and radiation
sensitive fuse elements are deposited on the pattern ad-
jacent flash lamp locations for simultaneous actuation of
each adjoining switch and fuse element by radiation being
emitted from an adjacent flash lamp. Accordingly, the
circuit arrangement of FIG. l is generally the same as
disclosed in the above referenced U.S. patents which in-
cludes a circuit board member 10, in the form of a die-
lectric substrate constructed with an organic polymer, havingconnector tabs 12 and 14 located at each end for insertion
of said circuit board member to an associated camera socket
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(not shown). The camera socket has contacts for con-
ductor lines 16, 18 and 20 of the lamp firing circuit
pattern to connect four flash lamps in parallel between
conductor lines 16 and 18 when connector tab 12 has been
inserted in the camera socket. Correspondingly, a second
group of four lamps is connected between conductor lines 18
` and 20 when connector tab 14 has been inserted into the
camera socket. Thus while an entire illustrative circuit
board is shown, there is need to discuss only a single group
of four flash lamps since the operation of the second group
of four flash lamps is essentially the mirror image of the
first group. Conductor lines 16 and 20 are interrupted by
radiation switches 22 to prevent the flash lamps in a group
from all being fired together on release of the camera
shutter. As can be noted, the switches 22 are each arranged
;~ in a region of a flash lamp termination 24 so that the heat
and light released when the flash lamp is fired operates to
convert the respective switch from a non-conductive to an
electrically-conductive state, thus establishing current
path to the next lamp to be flashed. Accordingly, when the
particular flash lamp in the circuit is flashed, then the
adjacent radiation switch is actuated providing a current
;~ path to the next lamp to be flashed. Each of the radiation
switches are in contact and bridge across the conductor lines
of the electrical circuit with material employed in the
radiation switch initially having an open circuit or high
resistance condition and with said resistance thereafter
` becoming zero or a low value when the material receives
~ radiation and/or heat from an adjacent flash lamp upon
30 firing of said lamp. It can also be noted that conductor
line 18 has deposited thereon fuse elements 26 at locations
proximate to the flash lamp terminations 24 so as to also
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be actuated by the heat and light released when the flash
lamp is fired. Circular shaped indentations 28 (shown in
~- phantom) surrounding each of said fuse elements 26 have been
formed on the opposite side of the circuit board member to
provide a lesser thickness than exists elsewhere on the
circuit board and thereby assist interruption of the circuit
path from conductor 18 to the already fired flash lamp. ~hen
the particular flash lamp adjacent to a given fuse element is
flashed, the radiation and/or heat created thereby is
absorbed by said fuse element causing the underlying sub-
strate of the conductor pattern as well as the circuit board
to either thermally melt or decompose and create a hole
or opening which permanently disrupts the electrical con-
necttion to the already fired flash lamp.
A more detailed description of the sequential firing
operation for the circuitry of a four-lamp group in the
above described circuit board can be provided in connection
with the schematic diagram shown in FIG. 2. Accordingly,
in FIG. 2 there is shown the flash lamps 24 electrically
connected in branch circuits to assure that the branch
circuit of each lamp will become an open circuit upon the
flashing of the lamp in that circuit. The desired mode
of operation is carried out starting with the leftmost
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branch circuit when the lamp in said circuit is flashed
` ` and causes fuse element 2~ in the same branch circuit to
physically interrupt the circuit path to said lamp while
simultaneously opening the circuit path to the flash lamp in
an adjacent branch circuit by actuating radiation sensitive
switch 22 in that branch circuit to the conductive state.
This cooperative action is repeated between successive
adjacent branches until all four lamps in the groups have
fired from simultaneous actuation of adjoining switch and
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fuse elements with radiation being emitted from an adjacent
flash lamp.
As previously indicated, a fuse element for operation
as above described can s:imply comprise a mass of radiation
absorbent material adhesively bonded to the eircuit pattern.
This can be accomplished with a physieal mixture of radiation
absorbent particulate solids with an organic polymer binder
and which can be adhered direetly to the dielectric substrate.
A satisfactory fuse material composition contains at least
20 percent or more of the radiation absorbent particulate solids
sueh as carbon black mixed with a eonventional liquid adhesive
; which hardens to a solid at ordinary temperatures. When
this fuse material composition is deposited direetly on the
eireuit pattern and allowed to harden at the loeations on
the eircuit board that have been recessed to enhance localized
melting or deeomposition of the underlying substrate, the
fuse aetuation produces a hole through the entire composite
medium. Interruption of the circuit path in this manner
can also be facilitated if the eonductor lines in the
braneh circuits for eaeh associated flash lamp are kept
to a minimum width or thickness~
While preferred embodiments of the invention have been
shown and described, various other embodiments and modifications
thereof will become apparent to persons skilled in the art.
For example, the desired circuit interruption can also be
i achieved by having the fuse elements deposited in physical
; contact with and bridging across spaced apart terminals
of the circuit pattern. It is therefore intended to limit -
the present invention only by the scope of the following
claims.
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