PRESSURE PLATES FOR CINEMATOGRAPH PROJECTORS

CADRES PRESSEURS POUR PROJECTEURS CINEMATOGRAPHIQUES

English Abstract

ABSTRACT OF THE DISCLOSURE
In a cinematographic film projector, there is
provided at the film gate an apertured pressure plate
which presses the film against a film guide. When
the film is arrested in the film gate to project a
stationary image formed by one film frame, heat emitted
from the light source tends to buckle the film causing
distortion of the image. To overcome or reduce buckling
in these circumstances, the pressure plate is provided
with a transparent member extending across the aperture
in the pressure plate to present to the film within the
area of the aperture a film contacting surface which
opposes buckling of the film within the area of the
aperture.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A cinematograph film projector comprising a film gate including film
guide means and an apertured pressure plate to press the film against the film
guide means, the pressure plate including a transparent member extending across
the aperture in the pressure plate to present to the film within the area of
the aperture in the plate a film contacting surface so disposed as to oppose
buckling of the film within the area of the aperture in the plate.
2. A projector according to claim 1, wherein the pressure plate includes
spaced parallel contact rails extending along opposite edges of the aperture
in the plate and having film contacting surfaces which contact the film along
the longitudinal edges thereof, and wherein the transparent member is located
between the rails with the film contacting surface of the transparent member
set back slightly in relation to the film contacting surfaces of the rails so
as to minimize contact with the film as the latter passes through the film gate.
3. A projector according to claim 2, wherein the contact rails of the
plate are upstanding from a flat base portion provided with the aperture of
the plate and wherein the transparent member is mounted on the base portion
on the same side thereof as the rails.
4. A projector according to claim 3, wherein the transparent member is
in the form of a transparent plate bridging the aperture in the base portion
and wherein the film contacting surface of the transparent member is flat over
the area of the aperture in the plate and is curved in a direction away from
the film at the entry and exit ends of the gate.
5. A projector according to claim 4, wherein each of the contact rails
on the pressure plate is formed with a longitudinally extending recess to

reduce the area of contact thereof with the film.
6. A projector according to claim 1, 2 or 3, comprising light source
means to produce an image of the film in the film gate, the light source
means being mounted on the same side of the film as the film guide means.
7. A projector according to claim 1, 2 or 3, wherein the transparent
member comprises a glass plate.

Description

1075941
This invention relates to pressure plates for supporting films
in film gates of cinematograph projectors which have the ability to
arrest movement of the film and to project a stationary image formed by
one frame of the stationary film.
In such projectors, heat emitted from the projection lamp
tends to buckle the film when the latter is stationary, causing
distortion of the image. This can generally be corrected by refocusing,
but the need to refocus each time the film is stopped or started represents
a considerable disadvantage which the present invention is intended to
overcome.
According to the invention a cinematograph film projector
comprises a film gate including film guide means and an apertured
pressure plate to press the film against the film guide means, the
pressure plate including a transparent member extending across the aperture
in the pressure plate to present to the film within the area of the
aperture in the plate a film contacting surface so disposed as to oppose
buckling of the film within the area of the aperture in the plate.
The transparent material is preferably glass. Said one
surface of the window is preferably slightly recessed with respect to
spaced contact rails of the plates so as to minimise abrasion of the film
as it passes over the window.
An exemplary embodiment of the invention will now be described
with reference to the accompanying drawings, in which:-
Figure 1 is a side view, partially in section, of the
film gate and surrounding structure of the projector,
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Figure 2 is an enlarged view of the pressure plate
shown in Figure 1,
Figure 3 is a fragmentary view as seen on the line
III-III of Figure 2, and
Figure 4 is a fragmentary sectional view taken on the
line IV-IV of Figure 3.
The projector has guide grooves 1 and 2 through which
the film 3 passes. Between the guide grooves 1 and 2 the
film passes through a film gate 4 where the image is projected
by light from a tungsten halogen projector lamp 5. The
pressure plate 6 is mounted at the film gate and has a
rectangular aperture 7 through which the image is projected
onto a screen (not shown). A heat filter moves into the
position shown in Figure 1 when movement of the film is
arrested and a stationary image from one frame is projected.
A rotatable shutter 9 has fingers 10 which impede the passage
of light each time a bar between adjacent frames of thè film
3 is passing the aperture 7.
The film passes between a film guide 12 and the pressure
plate 6 which is urged by two helical compression springs 13
towards the film guide 12 so as to maintain the film in a flat
condition when in the- film gate. A semi-circular plate 14 is
secured in the projector and serves as a fixed abutment for
the springs 13 which surround respective studs lS.
Referring to Figures 2 to 4, the pressure plate 6 is
in the form of an elongated strip of metal having a long-
itudinally extending shallow groove defined by a base 16
disposed between slightly raised longitudinally extending
contact rails 17 and 18. The contact rail 17 has a shallow
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recess 19 to reduce friction on the passing film 3, and the
other contact rail 18 has a deeper recess 20 to accommodate
the teeth of a rotatable sprocket which engages the sprocket
holes of the film 3 to drive the latter. The rectangular
aperture 7 is formed in the base 16 of the pressure plate 6.
In accordance with the invention, the aperture 7 is
covered with a glass window 22 one surface 23 of which engages
and supports the film 3 to prevent buckling of the film and
distortion of the image when the film is stationary. The
interposition of the heat filter 3 between the projector lamp
5 and the film gate when the film is stationary reduces the
amount of heat reaching the stationary film in the gate.
By using a pressure plate according to the invention
it has been found that the film 3 can be st!opped and a
stationary image projected without loss of focus for a period
of 25 seconds or more.
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