Optics: motion pictures – Shutters
Reexamination Certificate
1999-09-17
2001-10-02
Adams, Russell (Department: 2851)
Optics: motion pictures
Shutters
C352S208000, C352S219000, C353S088000
Reexamination Certificate
active
06296359
ABSTRACT:
The invention concerns a cinematic film projector and more particularly a projector of the type in which a film is moved step by step past an image window, and only when the image is stationary is it projected on to a screen. For this purpose a rotary shutter is provided. In addition, as a rule, an infrared filter is provided to limit the development of heat on the film.
The rotary shutter is synchronized with the film transport speed, so that only when an image is stationary is light released for image projection. The film transport speed is conventionally set at 24 images per second. As a result there is a certain flickering. This can be reduced in that even with a static image, a brief light beam interruption is carried out by a correspondingly designed rotary shutter. This can be achieved by a conventional mechanical rotary shutter, which for example has instead of only one light interruption, two or three light openings, and in this case we speak of a single blade shutter, double blade shutter, triple blade shutter. A single blade shutter which is made of metal rotates at triple speed and has a high inertia moment. Thus there is the danger of asymmetry, and given the necessary high rotational speed leads to problems of lack of balance.
Decisive for the degree of actinity, or in other words the efficiency with which the projector's light is effective for projecting an image on a wall or surface, is the magnitude of the dark sector. This dark sector depends on the switch ratio of the switch drive and corresponds to the timing of the film transporter K
B
. In addition there is the time span which is needed to cover the light beam before the beginning T
LA
and after the end T
LE
of the switch movement.
The time span of the dark sector T
G
:
(1) T
G
=T
LA
+T
B
+T
LE
single blade shutter
(2) T
G
=2 (T
LA
+T
B
+T
LE
) double blade shutter
(3) T
G
=3 (T
LA
+T
B
+T
LE
) triple blade shutter
In fact a triple blade shutter eliminates the flicker phenomena, but it reduces the degree of actinity E substantially.
(4) actinity degree E=dark phase/light phase
The cover times T
A
and T
E
are also taken into consideration in addition to the time T
B
which is multiplied by the number of the blades.
This additional effect can be reduced in the case of a three blade shutter by the use of a shutter with a single blade, but the blade is caused to rotate at three times the speed. In this way the light beam is interrupted three times per image, corresponding to a shutter frequency of 72 Hz.
Whereas the time T
B
remains the same (the time of the switch drive does not change) , the cover times T
A
and T
E
are reduced, because the angle which is necessary to cover and/or to release the beam of light remains constant, whereas the angular speed of the shutter increases.
For reasons of heat stability, rotary shutters are conventionally produced from metal. For a single blade shutter the rotational speed is shown as:
(5) v=3×24×60=4320 rpm.
These high rpm, in the case of an asymmetric single blade shutter, lead to substantial problems of lack of balance.
The invention is based on the object of designing a cinematic film projector in accordance with the preamble to claim
1
so that in the case of increased image interruption frequency, problems of imbalance can be avoided.
In accordance with the invention, the problem is solved by the features of claim
1
. Further embodiments of the invention are placed under protection in the subclaims.
In the subject of the invention, a rotation symmetrical rotary shutter is used, made of a heat-resistant light transparent material, preferably of glass. The rotary shutter has a single light transparent transmission window in the optical beam path, and the rotational speed is correspondingly increased against a three blade conventional mechanical shutter by three times. Thereby, instead of an image frequency of conventionally 24 images per second, the result is an image frequency of 72 images per second.
It should be mentioned that even a doubling of the image frequency by the provision of two transmission windows which are offset by 180°, and thus opposite each other, would already produce a clear improvement, in which an image frequency of 48 images per second would be attainable.
The light transparent material which is used provides the possibility of a coating, for example with infrared inhibiting material, in which a coating is only necessary in the transmission window, and the rest of the disk, for example, can be made light and heat impermeable by a corresponding coating or covering. The light attenuation due to the otherwise conventional additional infrared disk of glass of about 10% is thereby precisely compensated for.
The rotary shutter which is connected with the drive shaft of the motor can be accommodated in a small fixed housing, so that respectively there is a few mm of spacing from the walls. The housing can consist of two metallic half plates, which are opposite each other and are secured to the two ring edges of a small metal ring, preferably adhesively. One of the metallic half plates can be connected via a motor flange with the motor, for example adhesively. The two half plates have passage apertures opposite each other corresponding to the position of the transmission window of the rotary shutter. In centrically arranged recesses, each of the two metallic half plates can be provided with a motor adapter, one end of which is connected with the rotary shutter, while the other end of it is connected with the drive shaft of the motor.
The rotary shutter of glass which rotates between the two fixed metallic half plates passes over, with its transmission window, periodically per rotation the two opposite light passage windows of the half plates. Due to the small spacings from the wall, the air is drawn into the two gaps and it causes a cooling of the rotary shutter by up to 100° C. This makes it possible to use less temperature-resistant materials. Thereby the film, which is arranged before the rotary shutter, is also protected.
REFERENCES:
patent: 1883753 (1932-10-01), Basson
patent: 1884608 (1932-10-01), Dina
patent: 3791734 (1974-02-01), Mey
patent: 4350428 (1982-09-01), Phillips
patent: 5539488 (1996-07-01), Erickson et al.
Adams Russell
Ernemann CineTec GmbH
Fuller Rodney
Shlesinger Fitzsimmons & Shlesinger
LandOfFree
Cinematic film projector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cinematic film projector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cinematic film projector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2604479