Note: Descriptions are shown in the official language in which they were submitted.
23
FILM SHEET CASSETTE
This invention relate~ to a film sheet cassette
and, more particularly, to a cassette for handli~g film sheets
under daylight conditions and facilitating their imaglng.
There has been described in U.S. Patent 3 784 835
issued January 8, 1974 to Gunter Schmidt a film sheet cassette
that is particularly useful in x-ray appllcations and permits
the handling of film sheets under daylight conditions. The
cassette compri~es a houslng having a front plate and a back
plate in parallel spaced relation~hip. A pressure plate is
disposed between the front plate and the back plate and re-
slliently urged against the front plate in llghttight relation-
Rhip therewith. The cassette housing haæ channels formed along
opposite edges thereof for slideably receiving cam rods. The
; pressure plate is provided with follower studs along the edges
; thereof whlch rlde on cam surfaces of the rod~. Actuating
plns are provided on the cassette such that when they are
depressed they engage the cam rods and cause the~ to slide
within the channels such th~t the cam surfaces lift the fol-
lower studA and space the pressure plate from the front plate.
This permits the film sheets to be inserted into or removed
from the cassette.
While particularly unique and useful, Schmidt 18
ca~sette is adapted only for use with x-ray films. The front
plate and pressure plate are coated with fluorescent materials
which must be maintained in intimate contact with the film
sheets to transfer x-ray images formed thereon to the film.
In more recent y~ars, it has become psrticularly deslrable to
u~e daylightca~settes wlth other film systems, particularly
those used in medical applications such as axialto~ography.
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In axialtomography, a computer analyzes plural x-ray ~cansions
and forms a picture whlch i5 presented on a television~ e
display. The picture developed on the television screen is
then imaged, using a conventional camera, onto a film ca~sette
in the camera. The film in the cassette is then removed and
developed~ It would be particularly desirable to utilize a
cassette in con~unction with such cameras that is capable of
being handled under daylight conditions.
It is therefore an obJect of this invention to pro-
vide a film sheet cassette capable of handling photographlcfllms under daylight conditions.
Another ob~ect of this invention is to provide an
improved fllm sheet cassette.
In accordance with an embodiment of the inve~tlon,
a film sheet cassette ls constructed comprising a flat frame
defining an entrance forJ and an exposure aperture adapted to
support the edges of, a film sheet in a fixed focal planeJ a
pressure plate for reslliently bearing against said frame to
6ecure the edges of a film sheet between sald aperture and
said pressure plate, said pressure plate having at least one
cam follower, cam rod means defining at least one cam surface,
means mounting the cam rod mea~ on the frame for linear move-
ment wlth respect thereto between ~irst and second positions
and wlth the cam surface engaging said cam follower, said cam
surface being shaped to move the cam follower ~nd hence said
pressure plate a~ay from the aperture as the cam rod means
moves from said first to a said 6econd position~ a light shield
disposed ad~acent said film sheet entrance for preventing the
passage of light through said entrance to ~aid aperture and
said pressure plate when said cam rod means i~ in said flrst
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position, said ~rame defining elongated guide tracks along
said exposure aperture and an access slot, and a slide plate
adapted to be slideably inserted through said accese slot
into said guide tracks for blocking the pasQage of light
through said aperture.
In a partlcularly preferred embodiment, a detent
is provided on said frame to retain the ~lide plate in a
position blocking said aperture. Further, a light trap
means is positioned in said access slot to prevent the pas-
sage of light into the region con~iguous thepres~ure plate.The llght trap means is a flexible sheet, secured to the
frame at said access slot, yieldably engaging the slide plate.
The flexible sheet i5 for~ed to have a plurality of indlvidual
fingers, each engaging a portion of said slide plate.
In order that the invention may be more readlly
~nder~tood, the following description ls given merely by way
of example, reference being made to the a¢companging drawings,
in ~hich:
FIG. 1 i~ a plan view of the frame of a fllm sheet
cassette, the exposure aperture face down, constructed in
accordance with a preferred embodiment of this invention;
FIG. 2 ls a ~ectional view taken on the section line
2-2 of the film sheet cas6ette frame depicted in FIG. l;
FIG. 3 i~ a partial section view taken on the section
line 3-3 of the fllm sheet cassette frame depicted in FIG. 1~ -
~ IG. 4 is a partlal sectional view taken on section
line 4-4 of the film sheet cassette frame depicted in FIG. l;
FIG. 5 is an exploded pi¢torial vlew o~ a film sheet
cassette constructed in accordance with this invention using
3~ the frame of FIG. l;
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FIG. 6 ls a fragmentary side elevation view depict-
ing the operation of a cam rod used in the cassette depicted
in FIG. 5; and
FIG. 7 is a pictorial representation of the cassette
constructed ln accordance with this invention showlng the slide
partially withdrawn.
The lllustrated cassette is adapted to receive and
store photographic fllm sheets responsive to actinic radlation
(light) from an automatic film dispenser that preferably is ~ -
part of daylight film handling system sold by E.I. du Pont de
Nemours & Co. (Inc.), Wllmington, Delaware. Such dispenser
is described, ~or example, ln U.S. Patent 3,790,160 issued
February 5, 1974 to Gunter Schmidt. The film sheets used with
such system are appropriately notched and stacked as described
in U.S. Reissue Patent 28 438 to facilitate dispensing from
the lighttight dlspenser. The dispenser is capable of being
operated to open the envelope containing the fllm sheet stack
and dispensing the films individually into the cassette. The
dispenser cooper~tes with khe cas3ette to open the cassette
permitting a film ~3heet to be dropped therein, after which,
as the cassette is removed from the dispenser, the cassette
is again closed so as to be lighttight and permit the handling
of the fllm under daylight conditions. The cas~ette i8 then
placed in the back of a camera, a shield plate covering the
exposure aperture removed, the film exposed, the shield plate
replacedJ and the cassette removed from the camera for further
processing of the film. The cassette then may be inserted
lnto a sheet film storage magazine of the type described, for
example, in U.S. Patent 3,715,087 issued February 6, 1973,
also to Gunter Schmidt. The film may be developed or other-
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wise processed in the magazine. The advantage of the day-
light system, of course, is that a darkroom need not be used
to place the film into and remove it ~rom the cassette. This
results in a considerable time saving and iæ a real conven-
ience.
The cassette, according to this invention, include~
a lighttight hou~ing 10 which has an open exposure aperture
or window 12, through -which the film may be exposed, a remov-
able slide plate 14 adapted to block the window in a light-
tlght manner and a back plate 16. The housing has an entranceopening 18, through which the ~ilm may be inserted from the
film dispenser, and an access openlng or slot 20 through which
the slide plate 14 may be withdrawn to permit exposure of the
fil~.
The housing 10 includes a planar irame having U-
; ~haped cam channels 22 on elther side. A ~lared entrance
opening piece 24 a~d an access cross-member 26 ~oin the ends
o~ channels 22. The access cross-member 26 and the entrance
piece 24 are ~ecured to channels 22 by suitable epoxy cement.
Secured to the inner portion of the bottom edge (in the
drawing) o~ the frame are two rectangular window frames 30.
The wlndow ~rames 30 define trackæ 31 adapted to receive the
~llde plate 14 therein in a lighttight relationship. The
bottom portion Or the acces~ crQss-member 26 i8 sized to ~orm,
with a removable (by screws) plate 32, the access slot 20 as
well a~ continuation~ Or the tracks 31. A ~ixed plate 36 is
contiguous with the removable plate 32 ~nd epoxied to the
frame. m ese two plates 32 and 36 enclose a cavitg 38 ~or~ed
in the cross member 26 in which ls mounted a light shield 40.
The light shield 40 may be a reRilient, sprlng-like
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member formed, for example, of stainles~ steel, and secured
to the access cross-member 26 as by screw~ 42. me resilient
member 40 preferably ls formed so as to have flexible flngers ~ -
44. The flexible fingers are particularly deslrable in that
they permit the light trap to contact the sliding plate 14 at
a number of points across its wldth and the light trap does
not become bowed or otheFwise afrord access of light to the
cassette. The fingers preferably are covered with a sheet of
opaque velvet or plush-like material of well-known type to
10 facllitate the llght seal. The ~rame at the access slot 20
has formed thereon a nib 46 which functlon~ as a detent. The
nib 46 ls adapted to contact an enlarKed handle 48 formed on
one edge of the slide plate 14 to ~acilitdte its retention.
Such contact holds the slide plate in position securely so
that it does not inadvertently fall out.
To co~plete the descriptlon of the frame, cam rods
50J which may be ~ormed out Or ~heet metal, are L-shaped in
cross section and adapted to slide within the cam ch~nnels
22. Cam sur~aces 54 which, as wlll be described, are adapted
20 to engage cam follower tabs 56 on the pressure plate 58, are
similarly formed of sheet metal and welded or suitably
~ttached to the ca~ rods. The ends of the cam rods 50 con-
tl6suous the entrance openlng 18 have pins 60 inæerted i~ a
U-shAped receptacle formed in the ea~ rods to permlt the cam
rods to be actuated by mating plns (not shown) in the film
sheet dispenser or magazine. me inner walls of the cam
channels 22 are Approprlately cut away at 80 to permlt the
tabs 56 to be 61ideably lnserted therein and to provide
pivot ~tuds 61 for a palr of strlps 66 that are provided with
30 sprlng ~ingers 67. Fingers 67 normally bear against pressure
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plate 58 and hold it against ~rame 30. Strips 66 pivot ebout
studs 61 when cam rod~ 50 are actuated. Compre~sion springs
62 are positloned in the cam rods 50, and are retained at one
end by a tab (not shown) on the cam rods 50. Pins 64 are
insertable through the cam channels 22 and through ~lots 65
formed in the cam rod 50 to secure the remaining end of the
springs 62. ~us, when the cam rodæ are actuated, the springs
compress.
me cam rods 50 also carry pr~ssure plate actuating
~urfaces 70 positioned to engage fingerR 94 at the ends of
~trlps 66. When so engaged, the spring fingers 67 hold pres-
sure plate 58 against frame 30. me spring strips 66 have
aperture~ 90 at elther end whlch are adapted to ~it over the
studs 61 rormed ln the cam channels 22 B0 as to provide plvot
polnts.
As best sho~n in FIG. 6, cam surraces 54 engage
follower tabs 56 and move pressure plate 58 away from frame
30 when the cam rods are actuated. In addltlon, a lil3ht-trap
strip 74 (FIa. 5) has end tabs or pins 76 adapted to engage
notches or 610t8 78 rormed in the cam channels 22 Ruch that
the light-trap strip ~ay plvot between open and clo~ed posl-
tlons~ thereby openlng and closing the entrance opening 18
against li~
~he ll~ht-trap 74 i8 operated by the movement of
the pre~sure plate and has spring ~abs 79 which engage back
plate 16 and urge the li~ht-tr~p 74 normally to a closed
position bearing against Mared piece 24 until it i~ opened
by the ~ovement of the pressure plate to an open position
(away from the ~indow fr~me). Ihe pre~sure plate 58 has the
cam follo~er tabs 56 adapted to move within the limits of
slots 80 in the cam channels 22. ~e pressure plate 58 ls
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covered with a surface 59 on the film contact side that
provides an air layer between the film and the surface. m e
surface al~o should be non-electrostat~c such that the ~ilm
may slide ~reely across the surface of the pressure plate and
will, when the cassette is turned on end, drop freely out of
or into the cassette when the pressure plate is opened.
Such a sur~ace ~ay be made by adhering polyester
film to the film side of the pressure plate and coating the
film with a suspension that forms a stippled sur~ace. The
coating may be made by ~uspendlng silicon beads o~ about 1
mll diameter in a cellulose acetate solution. A suitable
black dye is added to reduce the tendency toward li~ht
piping between the ~ilm back and the surface. The beads
comprise about 1-2% by volume. The suspension ls applied to
the film on the pressure plate and allowed to dry. The sur-
face 59 is formed 80 that lts film backing extends slightly
beyond the end of the pressure plate and is bent back as at
71 to form together with the piece 24 (FIa. 3) of the frame
a flared opening for the fllm sheet.
The reverse side of the frame is adapted to receive
a backing plate 16 slideably therewith to complete the overall
enclosure. For this purpose, the back plate 16 ~s adapted to
slide in grooves 84 formed in the cam channels 22. The mem-
ber 26 1~ notched as at 43 to permit the ~llde plate 14 to
be withdrawn ~y gripping its handle 48. -~
In use, the pressure plate 58 normally engages the
edges of the window frame 30 80 as to secure a film sheet
(not shown) at its edges. The pressure plate engages such
edges due to the action of the compress~on spring 62, urging
the cam rod~ 50 toward the entrance opening 18 of the housing
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10. This ensures that the cam surfaces 54 are disengaged
~rom the cam follower tabs 56 (FIG. 6) and that the cam sur-
faces 70 engage the cam follower fingers 94 and plvot the
fingers 67 against the back of the pressure plate 58. At the
same time, the light-trap 74 is pivoted by the springs 79 to
close the entrance opening 18 to light. At this moment, the
spring strips 40 engage the slide plate 14 to prevent light
from entering the interior o~ the cassette in the region
between the pressure plate and window through that route.
The cassette is now placed into the back portion of
a ca~era for exposure and the slide plate 14 is wlthdrawn past
the detent nlb 46. As the slide plate is withdrawn, the
resilient strip 40 properly closes the opening to prevent
light irom entering the cassette. m e action of the individual
fingers ensures that no light is able to escape around the
edges and across the sur~ace Or the slide plate as it is
withdr~wn.
Followlng exposure, the reverse procedure is followed.
The sllde plate is re-introduced past the nib 46 into the access
openin~ 20 so as to close off the window and protect the exposed
fllm sheet against light. m e f~ct that during exposure the
iilm is able to re~t against the pressure plate and is ~irmly
held at all edge~, tends to hold the film ~heet, even though
it be relatlvely thin, in the focal plane o~ the optlcs o~
the camera. The retention of ~ocal plane holds even though
the cassette is turned wlth the film slde down. In short,
the cassette may be positioned in any orientation and still
rind advantageous use.
After the exposure and wlth the ~lide plate back in
position~ the cassette may be withdrawn ~rom the ca~era and
introduced into a fllm magazine of the type described by
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Schmidt. When it is introduced into this magazine, release
pins (not shown) engage the pins 60 such that they are de-
pre~sed into the cas~ette. Thls compresses the spr~ngs 62
and moves the cam surfaces 70, 54 so as to remove the pressure
of the spring str~p 66 against the pressure plate and lift the
pressure plate away from contact with the window edges. Up-
ward moYement o~ the pressure plate causes the light-trap 74
to plvot upwardly, tensioning its leaf springs, and pivotally
opens the light-trap 74 at the entrance opening 18. With the
cassette in a vertical orientation, with the entrance opening
downJ the fllm sheet slides freely out to the cassette across
the alr layer on the surface of the pressure plate.
The pressure plate itself i8 released partlcularly
by the withdrawal depicted by the dotted lines (FIG. 6) of the
cam surface 70 from contact with the spring strip cam follower
fingers 94 (FIG. 6) and the lifting cam 54 which engages the
tabs 56, causing them to be li~ted to the position represented
by the dotted lines in FIG. 6, thereby llftlng the pressure
plate away rrom cont~ct wlth the wlndow. It ls thus seen to
be a double actlon o~ release and positive actlon of the cam
surface which wlthdraws the pressure plate and opens the cas-
sette. When the cassette is to be reloaded, it is placed
entrance opening up, as described by Schmidt, in a dispenser.
The pins are again depressed, opening the entrance opening 18,
and a film sheet dropped in the cassette by the dispenser, all
under daylight conditlons. Upon removal from the dispenser,
the pins are released and the cassette is again ready ~or use.
The resulting cas~ette is a low-cost unit which i8
easily constructed and yet provides a sure lighttight seal for
the interior contents of the cassette. The lndividual resili-
ent ringers on the light-trap permit the ready removal o~ the
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slide plate 14 for taking pictures. The stippled, non-
electro~tatic surface of the pressure plate ensures an air
layer and ~ree slidability of the film for removal and with-
drawal of the film sheet. The film shee~ is releaseably
and firmly held by its edges in the desired ~ocal plane.
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