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1. * GB780081 (A)
Description: GB780081 (A) ? 1957-07-31
Improvements in and relating to cinematographic film-traction apparatus
Description of GB780081 (A)
PATENT SPECIFICATION
3 ____ E Dote of filing Complete specification Oct 24, 1955.
Application Date Oct. 22, 1954 Complete Specification Published July
31, 1957.
ld.c am accepz:ice:-Class 97(i), A11B.
780,081 No. 30543/54.
International Classification:-GO3b.
COMPLETE SPECIFICATION
Improvements in and relating to Cinematographic Film-Traction
Apparatus I, ARTHUR WILLIAM KINGSTON, a British subject of The Old
Mill House, Denham, Buckinghamshire, do hereby declare the invention,
for which I pray that a patent may be granted to me, and the method by
which it is to be perferomed, to be particularly described in and by
the following statement: -
The present invention relates to cinematographic film traction
apparatus of the type adapted to feed cinematographic film through a
film gate with a step-by-step motion such that in succession each
frame of the film enters the gate, remains in the gate for a
predetermined interval of time, and then leaves the gate to be
replaced by the next frame, the apparatus including a film engaging
member and means for drivng the film engaging member to cause the
latter to move the film through the film gate with the said
step-by-step motion. By frame is meant a part of the film upon which a
picture is to be recorded or has been recorded, as the case may be,
the part being one of a plurality of such parts along the length of
the film at spaced intervals.
Tn cinematographic film-traction apparatus of this type in common use,
the film engaging member comprises a claw adapted to engage in
perforations in the film. The driving means for driving the film
engaging member is then of the type comprising reciprocating means

2. including a driving member for imparting a reciprocatory motion to the
film engaging member, and engaging and disengaging means including a
driving member for moving the film engaging member into and out of
engagement with the film, the two motions being so related to one
another that, in operation, the film engaging member when brought into
engagement with the film moves the film in the desired direct!on
through the film gate. Such apparatus is widely used in the projection
of motion picture films on to a screen for direct viewing by an
audience.
Film traction apparatus of the type specified has also been employed
in the television trans[Price 3s. 6..1 mission of motion-pictures
recorded on cinematographic film. For this purpose, a light scanning
beam is focused on to the film in the film gate and through the film
on to a photo- M) electric cell and the beam is caused to scan the
film in the film gate in a manner well known in the art.
In television transmission of motion-picture films as carried out in
Great Britain, the light 55 scanning beam is arranged to scan the film
in the gate at the rate of 50 scans per second.
Since, however, a system of interlaced horizontal scanning is employed
in which the scanning beam is made to scan along alternate horizontal
lines of a picture during one scan and complete the scan by scanning
the remaining unscanned horizontal lines of the picture during the
next scan, complete scans, hereinafter referred to as frame-scans, are
made at only 65 half this rate, that is to say, at a rate of 25
frame-scans per second. In order to synchronise the appearance of the
frames of the film in the film gate with scanning times of the
scanning beam, the film traction apparatus 70 is arranged to feed film
through the film gate at the rate of 25 film frames per second, which
of course is one frame per second faster than the standard rate in
motion-picture practice.
In this way the scanning beam is able to make 75 one substantially
complete scan between successive feed movements of the film through
the film gate.
It has been found, however, that unless the film pull-down interval,
that is to say, the 80 timne taken to replace one frame in the film
gate by the next, can be made at least as short as the time between
the end of one scan and the beginning of the next, movement of the
film in the gate will be televised causing blurring of 85 the top or
bottom, or both top and bottom, of the televised picture. If a shutter
is employed to cut off projection during movement of the film in the
film gate, only alternate lines at the top or bottom, or both top and
bottom of the 90 televised picture will appear in the picture
transmitted.
780,081 The principal object of the present invention is to provide in

3. a cinematographic filmtraction apparatus of the type specified means
whereby the objectionable effects above referred to can be reduced.
According to the present invention, cinematographic film-traction
apparatus of the type specified, comprises a first coupling device
including a rotatably mounted driving member, a driven member mounted
for rotation about an axis parallel to but offset from the axis of
rotation of the driving member, and a driving connection between the
driving and driven members, said driving connection comprising a link
pivotally connected at one end to the driving member on an axis offset
from and parallel to the axis of rotation of the driving member and
pivotally connected at its other end to the driven member on an axis
offset from and parallel to the axis of the driven member, the
arrangement of the driving member, the driving connection and the
driven member being such that the driving member when rotating at
constant speed causes the driven member to rotate at a speed which
varies continuously between a maximum and minimum value, and the
driven member being coupled to the said means for driving the film
engaging member in such a manner that the driven member when moving at
the said maximum speed is in a position to cause the film engaging
member to move the film through the film gate, and a second coupling
device including a rotatably mounted driving member, a driven member
mounted for rotation about an axis parallel to but offset from the
axis of rotation of the driving member of the second device, and a
driving connection between the driving and driven members of the
second device, the last-mentioned driving connection comprising a link
pivotally connected at one end to the driving member of the second
device on an axis offset from and parallel to the axis of rotation
thereof and pivotally connected at the other end to the driven member
of the second device on an axis offset from and parallel to the axis
of rotation of the last-mentioned driven member, the arrangement of
the driving member, the driving connection and the driven member of
the second device being such that the driving member of the second
device when rotated at constant speed causes the driven member of the
second device to rotate at a speed which varies continuously between a
maximum and minimum value, and the driven member of the second device
being coupled to the driving member of the first coupling device in
such a manner that the driven member of the second device causes the
driving member of the first coupling device to move at maximum speed
when the latter member is in a position to move the driven member of
the first coupling device at maximum speed.
Where the said means for driving the film engaging member is of the
type specified, the driven member of the first coupling device is
coupled to the driving member of the reciprocatory means. The driving
member of the reciprocatory means may be a rotatable cam, the film

4. engaging member engaging said cam 70 and being mounted for sliding
movement in the desired direction of movement of film in the film
gate. The driving member of the engaging and disengaging means may be
adapted to be driven by the driven member of 75 the first coupling
device, and may comprise a cam-wheel having a peripheral contour, the
film engaging member engaging said contour and being mounted for
rocking movement about an axis parallel to the direction of movement
of film in the film gate.
An embodiment of the invention will now be described with reference to
the accompanying drawings in which Fig. 1 is a Perspective view of a
cinematographic film-traction apparatus according to the invention in
which parts of the housing and supports are shown cut away to reveal
the details of the two coupling devices.
Figs. 2a and 2b are side elevation and plan 90 view of the engaging
and disengaging mechanism employed in the apparatus shown in Fig.
1, and Figs. 3a and 3b are simplified perspective views of the two
coupling devices shown in 95 Fig. 1 showing the positions of minimum
and maximum speed respectively.
Fig. 1 shows a film-traction apparatus according to this invention,
applied to a cinematographic proejctor of conventional design. 104
Cinematographic film (not shown) passes in known manner down a
vertical film path in front of a rectangular aperture 12 (shown in
broken line) in a plate 13. The rectangular aperture 12 constitutes
the film gate and the 10' film is guided by guide rollers not shown so
as to pass in front of the aperture, perforations in the film Passing
in front of and along a vertical slit 14 formed in the plate 13
alongside the aperture 12. "o A film engaging member 15 in the form of
a hollow rectangular metal frame is mounted for rocking and sliding
movement on vertical guide pins 16 and 17. The size of the frame and
the disposition of the pins 16 and 17 are 11! such that projecting
parts 18, hereinafter referred to as the claw 18, passes into the slit
14.
A cam 19 having a shape approximately that of the sector of a circle
is fixedly mounted in 121 the region of its apex on the end of a
camshaft projecting through and rotatably mounted in a supporting face
plate 21 carried by the frame of the projector. On the other end of
the camshaft 20 is fixedly mounted a radially 12' extending arm 22.
The free end of the arm 22 is provided with a bearing which carries a
horizontally disposed pin 23 fixedly mounted on one end of a link 24.
A shaft 25 parallel to but offset from the camshaft 20 is rotatably
13( 780,081 mounted in a support 26 and carries at its end, adjacent
the link 24 a radially extending arm] 27. The free end of the arm 27
is provided with a bearing which carries a horizontally disposed pin
28 fixedly mounted on the other end of the link 24 and projecting in

5. the opposite direction to that of the pin 23.
The other end of the shaft 25 carries a radially extending arm 29
provided at its free end with a bearing which carries a horizontally
disposed pin 30 fixedly mounted on a further link 31. A further shaft
32 parallel to but offset from the shaft 25 is rotatably mounted in a
support 33, and has fixedly mounted on the end adjacent the arm 29 a
disc 34 (shown in broken line). The disc 34 is provided with a bearing
near its circumference, which carries a horizontally disposed pin 35
fixedly mounted on the other end of the link 31, the pin 35 extending
in the opposite direction to that of the pin 30. The shaft 32 is
driven by a motor (not shown) through a resilient coupling (not
shown).
The shaft 32 is in known manner coupled through reduction gears (not
shown) to a shaft for driving the film-carrying sprockets of the
projector.
A camwheel 36 having a peripheral groove 37 therein is fixedly mounted
on one end of a shaft not shown, which is driven through reduction
gears 38 and 39 form the camshaft 20. The gears 38 and 39 have a
reduction ratio of 1:2.
A cam follower part 40 of the film engaging member 15 engages in the
groove 37, and in conjunction therewith provides a means for rocking
the film engaging member 15 about the guide pins 16 and 17 to cause
the claw 18 alternately to engage and disengage the perfora4( tions in
the film (not shown) on the other side of the plate 13.
The camwheel 36 and the film engaging member 15 are shown in detail in
Figs. 2a and 2b. The groove 37 in the rim of the camwheel 4 36 is
displaced laterally over a region shown in Fig. 2b by the angle X
which the displaced portion subtends.
In operation, the motor (not shown) is run at constant speed at 50
revolutions per second.
SO The shaft 32 which is driven by the motor through the resilient
coupling (not shown) rotates the disc 34 at constant angular speed.
The pin 35 being rotatably mounted in the disc 34 describes a circle
about the shaft 32 5S at the constant angular speed, causing the link
31 to rotate the arm 29 at a speed which varies continuously between a
maximum and minimum value during each revolution. The shaft 25 driven
by the arm 29 rotates the arm 27 at this varying angular speed. The
pin 28 being rotatably mounted in the free end of the arm 27 is
constrained to move in a circle about the shaft 25, causing the link
24 to rotate the arm 22 at a speed which varies continuously between a
maximum and minimum value during each revolution. The camshaft 20 is
rotated by the arm 20 at this continuously varying angular speed,
causing the cam 19 to impart a reciprocatory motion to the film
engaging member 15, in which the downward movement 70 of the member 15

6. is effected at maximum speed.
Two positions of minimum and maximum speeds of the two coupling
devices shown in Fig. 1 are shown schematically in Pigs. 3a and 3b.
The position shown in Fig. 3a is the position of minimum speed. The
position shown in Fig. 3b is the position of maximum speed.
It will be seen from Fig. 3b that the arm 29 is in a position to be
moved at maximum speed when the arm 22 is in a position to be moved 80
at maximum speed.
The camwheel 36 which is driven by the camshaft 20 through reduction
gears 38 and 39 makes one revolution for every two revolutions of the
cam 29, and by rocking the film engaging member 15 about the guide
pins 16 and 17 causes the claw 18 to engage the film for a period
during each revolution of the camwheel.
The arrangement is such that the rocking of the film engaging member
15 by the camwheel 90 36 coincides with the downward movements
imparted to the film engaging member 15 by the cam 19. It will be
apparent, however, that since the camwheel 36 makes only 25
revolutions per second, the claw 18 is caused to 95 engage the film
only during every alternate downward movement of the film engaging
member 15. The film is thus fed through the film gate 12 at the rate
of 25 frames per second.
The apparatus shown in Fig. 1 may be lOG employed in conjunction with
television transmission apparatus operating at 25 frame scans per
second for televising pictures recorded on cinematographic film. A "
flying spot " scanner is placed in front of the projection apparatus
105 shown in Fig. 1 and so arranged that the scanning light beam
traverses the film in the film gate. The operation of the
film-traction apparatus and the flying spot scanner are synchronised
so that the film is pulled down in 110 the film gate during the
fly-back interval of the scanning beam. The scanning beam having
passed through the film in the film gate is deflected through 900 by a
prism (not shown) and directed on to a photo-cell to produce
television picture signals for transmission.
The embodiment described with reference to Fig. 1 may be modified in a
variety of ways.
In order to obtain a still higher pulldown speed, it can be arranged
for the apparatus to be 120 operated at say 75 revolutions per second
and arranging by suitable choice of reduction gearing to rotate the
camwheel at 25 revolutions per second, whereby the claw 18 becomes
operative in pulling down film only once every 125 three downward
movements of the film engaging member 15.
The apparatus can equally well be adapted to pull film through the
film gate with irregular step-by-step motion. Irregular step-by-step
130 780,081 motion of the film is necessary if the apparatus is to be

7. employed in the television transmission of motion-picture film in
which the television has a frame-scan of 30 frame scans per second as
in the case in Canada and in the U.S.A. It will be appreciated that it
is not possible to increase the film projection rate to 30 frames per
second without making the motion in the picture appear unnatural. This
difficulty can however be overcome by making the time between
successive film movements alternately / i and 1I,0 sec. so that the
average projection rate of the film remains at 24 frames per second.
During the interval of '/.fth second, the scanning beam of the
television apparatus makes 3 scans, that is to say, 1./ frame-scans,
and during the interval '1/,, second the scanning beam makes one
complete frame scan.
The embodiment described can be modified to give such an irregular
step-by-step motion of the film by arranging that the claw makes
pull-down movements per second but is operative in pulling the film
down during the first and third downward movements in every five. This
may, for example, be achieved by substituting the camwheel 36 shown in
Figs. 1 and 2a and 2b which imparts rocking movement to the film
engaging member 15 by a camwheel having a groove along its rim which
is laterally displaced over two regions which divide the circumference
of the camwheel in the ratio 2:3. Such a camwheel when rotated at 12
revolutions per second can be arranged to cause the claw 18 of the
film engaging mem3S ber 15 to engage the film during the first and
third downward movements in every five successive downward movements
of the film engaging member 15. The film is thereby moved through the
film gate with an irregular step-by-step motion at the average rate of
24 frames per second.
It will be appreciated that cinematographic film traction apparatus
according to this invention may equally well be employed in
conjunction with television apparatus for recording televised pictures
directly on to cinematographic film. Unexposed film on which televised
pictures are to be recorded is fed through the film gate in the manner
hereinbefore described and the scanning beam from a " flying spot "
scanner, modulated in intensity in accordance with the transmitted
picture signals, is caused to scan the film in the film gate, the
operation of the to scanner and film traction apparatus being
synchronised so that the film is pulled down during the fly-back
interval of the scanning beam.
It is a well known fact that when using conventional cinematographic
projection apparatus for the projection of motion-picture films on to
a screen for direct viewing movement of the film in the film gate may
be detected in the projected picture unless a shutter is employed to
cut off projection during the intervals when the film is being moved
through the gate. In order to reduce flicker effects it is desirable

8. to employ a multi-bladed rotatable shutter in which the blades of the
shutter subtend equal angles and are spaced by equal 70 gaps
subtending angles equal to those of the blades. Two-bladed shutters in
which the blades each subtend an angle of 900 and are spaced by 90A
gaps are in common use. A three-bladed shutter each blade of which
subtends an angle of 60' and is spaced from the next blade by a 60-
gap has also been proposed for use with apparatus in which the
pull-down interval is shortened by doubling or trebling the overall
speed of the apparatus and causing 80 the claw to engage the film
every alternate or third downward movement.
Apparatus according to the present invention operating at normal speed
may however he advantageously employed with balanced 85 shutters of
three or more blades due to the greatly reduced pull-down interval,
thereby greatly reducing any flicker effect.
It has also been found that when cinematographic film-traction
apparatus according to 90 this invention is employed for projecting of
motion-picture films on to a screen for direct viewing movement of the
film in the film gate may be sufficiently fast to avoid detection in
the projected picture, and a shutter may not be 95 required.
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