July 17, 1951
A- V- BEDFORD
INTERMITTENT FILM ADVANCING MECHANISM
UTILIZING AIR PRESSURE
Filed March 22, 1949
2,560,919
2 Sheets-Sheet 1
INVENTOR
19
-
A104 L/?'ID/I'OBD
"WK/4d”
Air/‘navy
Patented July 17, 1951
2,560,919
UNITED STATES PATENT OFFICE
2.560.919
INTERMI'I‘TENT FILM ADVANCING MECH
ANISM UTILIZING AIR PRESSURE
Aida V. Bedford, Princeton, N. 1., assignor to
Radio Corporation of America, a corporation
of Delaware .
Application March 22, m9, Serial No. 82,867
6 Claims. (CI. 88-18)
1
2
.
This invention relates to motion picture ?lm
apparatus, and particularly to a motion picture
?lm projector having an intermittent pull-down
mechanism with extremely short pull-down
periods.
Fig. 1 is an elevational view, partly in cross
section, of the pull-down mechanism embodying
the invention.
'
- Fig. 2 is a detailed view of the lower loop form
ing‘ portion of the intermittent mechanism of the
7
The application is directed to improvements of
the rapid pull-down mechanism disclosed and
invention.
1
"
Fig. 3 is a detailed view of the air ports for
claimed in co-pending application, - Ser. No.
forming the ?lm loops, taken along the line 2-2
82,866, ?led March 22, 1949. In this co-pending
of Fig. 2, and
application, the pull-down is accomplished by a 10
Fig. 4 is a chart showing the relative operation
blast of air under pressure, the ?lm being previ
times of the various elements of the mechanism
ously formed into a loop one frame long just
in relation to a television scanning system.
ahead of the ?lm gate, the ?lm thus being ad;
Referring now to the drawings, in which the
vanced one frame into the gate aperture. Since
the advancement of one frame is made in about
one twelve-hundredth of a second, improvements
have been provided to obtain better control of
same numerals identify like elements, a motion
picture‘ film 8, of either the thirty-?ve milli
meter or sixteen millimeter type, passes over a
continuously rotating sprocket 9, under pad
the air blast and of the acceleration and deceler
rollers III, the ?lm then passing into a loop l2
ation of the one frame ?lm loop. Thus, a
, and man intermittently driven sprocket l3 with
smoother action and more protection for the ?lm 20 its associated pad rollers II. The ?lm then
are provided.
passes between the guide end of a gate shoe l6
The mechanism is suitable for the normal pro
and a guide ii to a projection aperture I! be
jection of motion picture ?lm without the usual
tween the gate shoes IG and 24, the ?lm forming
light interrupting shutter and for use in a tele
into a loop between the guide l5 and shoes "-2
vision scanning system of the ?ylng spot type. 25
The invention is being described in association
with the latter system for purposes of illustra
tion, the air and ?lm loop controls operating the
same for any use of the projector.
4,7.
as will be described hereinafter.
"
After passing the projection aperture l9, the
?lm will be formed into a lower loop, as will be
described later, and will then pass between a
guide 22 and a guide 34 to an intermittent
The principal object of the invention, there 30 sprocket 25 with its associated pad roller 26.
fore, is to facilitate the intermittent positioning
The ?lm then passes into a lower loop 21 from
of the frames of a motion picture ?lm in a pro
which it is taken by a continuously rotating
jection aperture.
sprocket 28 having pad rollers 29. Thus, the
Another object Of the invention is to provide ' ?lm is continuously and uniformly driven, by‘
improved air and ?lm loop controls for a rapid 35 sprockets 9 and 28, and intermittently advanced
pull-down mechanism for a motion picture pro
by sprockets l3 and 25. Through guide IS, a
jector.
,
clamp |‘| passes; through shoe 24, clamps 2|! and
A further object of the invention is to provide
2| pass; and through guide 34, a clamp 23 passes.
an improved means for rapidly changing picture
Clamps ll, 20, 2|, and 23 are actuated by a re
frames on a motion picture ?lm in a projection 40 spective plurality of cams 30, 3|, 32,. and 33.
aperture by an air blast having special port and
The clamps may contact the ?lm along its edge
?lm loop controls.
or along a narrow strip between adjacent frames
-A still further object of the invention is to
to prevent scratching of the ?lm. Although
provide an improved type of air and ?lm loop _, clamps 2|! and 2| are shown at the aperture is to
controls for an intermittent ?lm mechanism, 45 hold the ?lm 8 stationary in the aperture during
which provides a pull-down time of the order of
the forming of a loop above it, the friction be
one-thousandth of a second.
.
tween shoes IS and 24 could be such that the"
clamps 20 and 2| are unnecessary.
'
Although the novel features which are believed
to be characteristic of this invention will be
An air chamber of trapezoidal shape is formed
pointed out with particularity in the appended 50 by an annular housing plate 35 and an end plate
claims, the manner of its organization and the
38, the latter having an air intake pipe 21, which
mode of its operation will be better understood
will admit air under pressure to a chamber 32.
by referring to the following description, read in
conjunction with the accompanying drawings,
forming a part hereof, in which:
Inside the chamber, formed by the plates :5; and
38, is an inner, rotatable sleeve or port member
The
55 42 and an outer sleeve or port member 4|.
2,660,019
port members may be rotated in any suitable
of a second after clamps '20 and 2| are applied
manner, such as port member 42 by a shaft 44
and clamps H and 23 are released, the same
connected to the member 42 by a ?ange 45 and
cycle as just described occurs, there being a sub
sequent idle period of .0035 second before cer
screws, such as shown at 65, and port member 4|
by a cylindrical extension of the member 4| con 5 tain ports are again aligned to advance the ?lm
centric of the shaft 44. Bearing sleeves 49 and
another frame. Thus, in the ?rst two-sixtieths
50 separate the members 4| and 42 from the
second, the ?rst frame is scanned twice, and
shaft 44 and housing plate 35. Referring to Figs.
during the next three-sixtieths second, the ?lm
is scanned three times. The five scanning peri
2 and 3, the port member 4| has a port 53 therein,
the port member 42 has a port 54 therein, and 10 ods thus correspond to two picture frames photo
graphed in one twenty-fourth second each, in
housing 35 has a port 55 therein. Extending
cluding the camera pull~down time.
from port 55, are funnel flanges 55 on walls 65
To obtain the intermittent sprocket and cam
and 56 shown in Figs. 1 and 2. - Similar walls 09,
action, the sprockets and cams are geared to
without the runnel, are shown in Fig. 1.
The ?lm advancement cycle will be described 15 gether in the proper ratios. However, to obtain
the air blast at one-thirtieth and one-twentieth
in connection with the chart shown in Fig. 4,
second time cycles, it has been found that the
to which reference will now be made, this chart
inner sleeve 42 may be provided with one aper
showing the relationship between the pull-down
ture 54, the sleeve rotating at a,rate of forty
periods and the scanning periods of a television
?ying spot system; although, for normal motion 20 eight revolutions per second, while the sleeve 4|
is provided with two apertures spaced 144 de
picture projection, the pull-down periods may
'grees apart, the sleeve 4| rotating at a speed of
be uniform or equally spaced. First, starting at
sixty revolutions per second in the opposite di
the instant after the positioning of a. frame in
the aperture l9 and the beginning of a television
scanning period, the clamps 20 and 2| are ap
plied by cams 3| and 32 to hold the film sta
tionary in the gate, and clamps I1 and 23 are
released by cams 30 and 33 so that loops may be
formed. This action is performed in approxi
rection to sleeve 42. At these two rates of speed
and aperture placements, there will be an align
ment of apertures at stationary aperture 55 after
one-thirtieth of a second, and then after one
twentieth of a second, these time periods alter
nating in serial order.
Although only a single port is shown at 53,
mately .011 second, after which sprockets l3 30
54, and 55, it is to be understood that these
and 25 are rotated for approximately .010 sec
ports may consist of a plurality of smaller open
ond to form an upper loop, as shown by the
ings aligned in the direction of rotation of the
double broken lines 68, and to remove the lower
sleeves so that the ports may be opened very
loop to the position shown by double broken
lines 60. In the next,.011 second, clamps I1 35 rapidly in a small distance of travel. By the
use of double port members rotating in opposite
and 23 are applied and clamps 20 and 2| are re
directions, the diameters of the members may
leased in preparation for the advancement of a
be much less than that of a single disc, as dis
?lm frame, the sprocket I! having previously
closed in the above mentioned co-pending ap
advanced that length of ?lm into loop 58. Dur
ing these three time periods, the image on the 40 plication.
It has been found that, with a double claw
fraine of ?lm in the aperture is has been
pulling on a pair of sprocket holes, the sprocket
scanned twice.
>
holes would tear out at a pull of ten pounds,
The next action is the "blow down," and this
and less than that, if the pull is uneven. In tests
occurs when the port 53 in sleeve 4| and port
54 in sleeve 42 coincide with port 55. As shown 45 of ?lm tensile strength, however, it has been
found that one hundred to one hundred and ten
in Fig. 3, the ?lm, in position 50, rests on the
pounds pull may be applied to thirty-?ve milli
ends of funnel ?anges 56 of wall 65 and 56 when
meter ?lm. It was also found that the tensile
advanced by sprocket 25. When the air from
strength of splices were greater than for the
chamber 39 is applied to the ?lm, it is blown
to position 52, shown by the double solid lines 50 film itself. In the present invention, a pull of
only twenty pounds is required to move va seven
in Fig. 2 and broken lines in Figs. 2 and 3, by the
inch length of ?lm the height of one frame within
air blast in about .001 second. It will be noted
one-thousandth of a second. Thus, a safety
‘that, when the ?lm has reached the end of the
factor of ?ve has been provided.
walls 65 and 56, the air from ports 53, 54, and
With respect to the air pressure required to
55 exhausts past the ends of the pair of walls 55
move a seven inch length of ?lm the height of
55 and 56. which will reduce the pressure on the
a frame in one-thousandth of a second, it was
?lm and aid in gradually slowing it down or
calculated that a pressure of thirty-two pounds
decelerating it to its stop position at 52. To
per square inch is required, the maximum port
aid in the deceleration, the loop 08 will reach
the edges of walls 59 at about the same time the 60 area being 1.5 square inch. Since the air leaks
through the sprocket holes, and, after passing
loopiiB-BI reaches the edges of walls 55 and
the guides 65 and G6, blows past the ?lm, the
56, and air will be entrapped within a chamber
?lm is accelerated during approximately one
enclosed by walls 59, shoe l5, and the ?lm. To
half of the blow-down period and decelerated
obtain the proper rate of deceleration, a plu
rality of holes 'H are drilled in the shoe IE to 85 during the remainder of this period at a sub
stantially linear rate.
control the escape of air from the chamber, the
There is thus provided an intermittent ?lm
?lm thus being gently brought to rest on the
shoe l5.
advancing mechanism or film pull-down mech
anism in which the pull-down period may be
Now, continuing the ?lm advancement cycle
over two frames, for the next .0085 second, the 70 made very rapid, such as of the order of one
mechanism is idle as far as clamps and inter
thousandth second. This rate is sufficiently fast
mittent sprockets are concerned; it being real
to permit the projection of motion picture ?lm
ized, of course, that sleeve 4| and 42 and
without a shutter for eliminating objectionable
sprockets 5 and 28 continue to rotate and scan
light during this period, since the action of the
ning proceeds. Thus, starting one twenty-fourth 75 ?lm is not observable, and is also of a time
2,660,919
5
period which permits the use of the ?ying spot
type of televsion scanning.
6
4. A mechanism for controlling the intermit
tent rapid movement of a portion of a ?lm strip
from one position to another position, compris
I claim:
ing a pair of path sections having walls through
1. A motion picture projector adapted to have
which the ?lm travels for entrapping air between
?lm advanced into an aperture thereof intermit
said walls'of said sections and portions of said
tently, comprising a ?lm path structure, a ?rst
?lm strip, a ?lm gate positioned between said
intermittent sprocket, a second intermittent
sections, an air source, means for controlling
sprocket, gate means for holding said ?lm sta
the entrance of air into one of said sections to
tionary in said gate during a predetermined time
period, means for producing air under pressure, 10 move the portion of the ?lm entrapping the air
therein into a loop to move the ?lm portion in
a chamber between said gate and said second in—
said gate out of said gate, said ?lm loop portion
termittent sprocket to entrap air and formed by
releasing said air when said loop portion has
certain walls of said structure and a portion of
moved over ahcertain distance of its travel, said
said ?lm, a pair of rotatable valve members for
controlling air to said chamber, one of said walls 15 movement of "said gate portion and loop portion
of said strip moving a third portion of said strip
having a port therein adapted to permit air to
into said other ?lm path section to entrap air
pass into said chamber at predetermined inter
therein when moved over a portion of its travel,
vals for blowing said ?lm into a free 100p be—
and means for determining the rate of escape
tween said gate and said second intermittent
sprocket, and a second chamber between said 20 ment of said entrapped air in said other section.
5. A mechanism in accordance with claim 4,
gate and said ?rst intermittent sprocket to en
in which said sections have parallel side walls,
trap air and formed by other walls of said struc
the edges of said respective portions of said ?lm
ture and a portion of said ?lm between said
being movable adjacent said walls, the depth of
gate and said ?rst intermittent sprocket, air be
ing entrapped during substantially one-half the 25 said walls being approximately one-half the
length of the total movement of the ?lm loop
period of time required to eliminate said loop in
portions.
said second chamber.
6. A mechanism in ‘accordance with claim 4, in
2. A motion picture projector in accordance
which said last mentioned means is an apertured
with claim 1, in which said ?rst mentioned cham
ber comprises parallel side walls extending sub 30 wall of said other section in which said air
is entrapped, air being entrapped in said other
stantially one-half the distance between the ex
section at approximately the same instant the
treme positions of said ?rst mentioned ?lm loop
air is released from said ?rst section.
and said second mentioned chamber having par
ALDA V. BEDFORD.
allel side walls extending substantially one-half
the distance between the extreme positions of said 35
REFERENCES CITED’
second mentioned loop, said second mentioned
The following references are of record in the
chamber having air passages therein to control
?le of this patent:
the deceleration of said ?lm into said second men
tioned chamber by determining the rate of escape
UNITED STATES PATENTS
40
ment of air from said second mentioned chamber.
Number
7 Name
Date
3. A motion picture projector in accordance
960,794
Bingham __________ __ June 7, 1910
with claim 1, in which said rotatable valve mem
1,244,920
Thomas __________ __ Oct. 30, 1917
bers rotate in opposite directions, one of said
1,309,471
Evans ____________ __ July 8, 1919
members having a different number of ports 45 1,393,735
Anselmi et al. ______ Oct. 18. 1921
therein than the other of said members, said
FOREIGN
PATENTS
members rotating at different speeds to provide
Number
Country
Date
unequal time periods between the openings of
10,266
Great Britain __________ _- of 1915
said valve members.