US2447839A

US2447839A - Drive mechanism for the intermittent movement in a television motion-picture projector

Info

Publication number: US2447839A
Application number: US615671A
Authority: US
Inventors: Frank J Bingley
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1945-09-11
Filing date: 1945-09-11
Publication date: 1948-08-24
Anticipated expiration: 1965-08-24

Description

Aug. 24, 1948. F. J. BINGLEY 2,447,339

DRIVE MECHANISM FOR THE INTEHMITTENT MOVEMENT IN A TELEVISION MOTION PICTURE PROJECTOR Filed Sept. l1, 1945 Patented Aug. 24, 1 948 DRIVE MECHANISM FOR THE INTEBMIT- TENT MOVEMENT IN A TELEVISION MO- TION-PICTURE PROJECTOR Frank J. Bingley, Philadelphia, Pa., assignor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Pennsyl- Vania Application September 11, 1945, Serial No. 615,671

5 Claims. 1

This invention has to do with television and particularly with motion picture projectors adapted for use in'television broadcasting systems.

For various reasons known to those skilled in the art, television cameras are designed to generate television signals at the rate of 60 fields per second, interlaced, or, in other words, 30 complete frames per second. On the other hand standard motion picture projectors are designed to expose 24 frames per second. Therefore, when transmitting standard motion picture nlm by television, it is necessary to do so by some method rwhereby the scanning rate of the television system is -correlated with the normal exposure rate of the film so that a desirable reproduction will appear at the television receiver.

There are several methods by which this may be accomplished, only one of which, however, so far as applicant is aware, makes use of intermittent lm motion for advancing successive frames into position to be projected upon the screen of the cathode ray tube. Such intermittent motion frame for each complete revolution thereof and, as stated above, at the rate of 24 frames per second, when employed in motion picture practice.

To correlate the different rates of scanning and projection, as between the television camera andthe motion picture projector, respectively, Bedford makes use of a varying rate of exposure for successive lm frames. To accommodate the 60 fields per second scanning rate of the television projector to the 24 exposures per second of the motion picture projectors, he projects (at the rate of one projection for each one-sixtieth of a is employed in interlaced systems of scanning. and

it is with this type of apparatus that the present invention is primarily concerned.

Such a. system is the subject of Patent No. 2,082,093, issued June 1, 1937, to A. V. Bedford, and also of an article entitled Application of motion-picture film to television, by E. W. Engstrom etal., and appearing, beginning with page 48, in the RCA Review, volume 4, 1939-40. The system disclosed in these publications has been adopted in the art as being the best previously known method for broadcasting standard motion picture nlm by television. Its operation, however,

' depends upon a modification of the well known Powers intermittent movement. This movement has proved disadvantageous because of its unreliable operation and high manufacturing cost.

When used in standard motion picture projection machines the Powers cam has only one lobe for turning the nlm sprocket, which is moved one-quarter of a revolution for each complete revolution of the cam. This quarter of a revolution is accomplished at high speed and moves the next frame into position to be projected upon the screen at the time the solid portion of the shutter is passing through the light beam of the projector. Ihe high speed is necessary to permit each frame to remain at rest in projection position for as long a period oftime as possible. Thus we see that an unmodied Powers intermittent movement normally exposes one picture second) an image of each odd motion picture frame twice in succession upon the mosaic screen of the cathode-ray, or camera tube, and an image of each even frame three times upon the screen, all during stationary periods of the film.A

Correct timing of these projections upon the screen, as taught in the Bedford system, is accomplis'hed by modifying the Powers intermittent movement to include on the cam two lobes spaced 144 degrees apart. Thus for each Ysingle revolution of the cam, two frames will have' moved into position for projection necessitating a lreduction in the R. P. S. of the intermittent movement to twelve instead of the normal twen- -ty-four. For each revolution of the intermittent movement two frames are exposed or projected for scanning, one of which is scanned twice (consuming two-sixteths of a second) during the time the follower is passing through the 144 angle between the lobes, and the other is scanned three times (consuming three-sixtieths of a second) during the time the follower is passing through the remaining angle of 216. Therefore, at the end of each twelve revolutions of the cam, and at the end of each second, a total of sixty fields have been scanned for each twenty-four frames of motion pictures exposed.

One of the chief faults found in this system is the necessary reduction by one-half in the number of revolutions per second, which increases two-fold the pull-down time for moving each successive frame into position for projection and decreases to an undesirable degree, the working tolerances, i. e., the time between pull-down and exposure.

The Powers intermittent movement is no longer widely used in motion picture projectors. Its use in television has been tolerated, heretofore, only for want of `a better system in which the more desirable intermittent movements may be incorporated, and hence, with the foregoing in mind, it is an important object of the present invention to provide an improved motion picture 3 projector for use in television broadcasting systems.

Another important object of the invention is the provision of such a projector in which standard, unmodified, intermittent movements may be employed.

A further object of the invention is to provide such a projector which is characterized by its simplicity and its efficient mode of operation.

To the foregoing general ends the present invention proposes to use an unmodified intermittent movement, but to modulate the velocity of its driving shaft so that, while its average rotation is the normal 1440 R. P. M., or 24 R. P. S., successive revolutions are faster and slower, respectively, with the result that pull-downs will occur at appropriate intervals, permitting two projections of the odd'frames upon the mosaic screen of the camera tube during the fast revolutions, and three projections of the even frames upon the screen during the slow revolutions, at the rate of sixty projections per second of twenty-four picture frames.

It will now be well understood that, prior to this invention, television transmission of standard motion picture lm, as far as the intermittent filmmotion types are concerned, has been completely dependent upon the aforesaid modied Powers intermittent movement, but that with the introduction of the present invention the necessity for using this modified intermittent movementv is eliminated, and the use of the more desirable intermittent movements, such as, for example, the well known and superior Geneva" movement, is made possible. It should be further understood however, that, as a result of the present invention, any of the well known intermittent movements, including the unmodied Powers, may conveniently be used in the projector of the instant invention. When the "Powers movement is employed, in conjunction with the apparatus of the present invention, the necessity of reducing the normal R. P. S. by half, is obi/lated.

In the drawings:

Figure 1 illustrates diagrammatically the preferred embodiment of the invention;

Figure 2 is a sectional view on an enlarged scale, taken substantially as indicated bythe line 2-2 in Figure 1;

Figure 3 is a fragmentary view on an enlarged scale, and partially in section, illustrating the preferred Geneva type of intermittent movement; and,

' Figure 4 is a sectional view taken substantially as indicated by the line 4--4 in Figure 3.

More specifically, and with particular reference to the details in Figure 1 of the drawings, the numeral IIJ designates a motion-picture projector adapted to project successive picture images intermittently upon a photo-sensitive screen II of a cathode ray, or camera tube I2, positioned within a television camera I3. Each of these images is scanned in the usual well known manner by a moving beam of electrons, developed ,in the electron gun It .if tube I2, thus to generate the necessary picture signals for broadcast by the transmitter (not shown).

As pointed out heretofore, when broadcasting standard motion picture film by television it is necessary to correlate the exposure speed of 24 frames per second for normal motion picture projection with the scanning rate of 60 elds per second for television systems. In the present invention this correlation is accomplished in the novel manner hereinafter described.

The motion picture film I5 is moved into projection position in the film gate i511, intermittently, at the rate of twenty-four frames per second by a. pull-down sprocket I6 which is operated by a standard intermittent device II. As illustrated, this device is of the highly desirable Geneva type, although it should again be clearly understood that any suitable standard intermittent movement may be used, such as, for example, the standard unmodified Powers type above referred to. These intermittent movements are well known in both the motion picture and television arts and it is believed that a detailed description thereof is unnecessary to a complete understanding of the present invention. However, a brief description of the Geneva" type illustrated, will serve to point out its salient features as related to the present invention.

With particular reference to Figures 3 and 4, which illustrate the type of Geneva intermittent movement best serving the purposes of the invention, the numeral I8 designates the housing therefor, while the intermittent movement itself consists of a Maltese cross I9, more commonly referred to as the star, and a cam 20 upon which is mounted a master pin 2|, adapted to drive the star. This cam is also provided with a at circular surface, or cam ring 22, by means of which the star, and therefore the intermittent sprocket I6, both of which are mounted upon shaft 23, are locked in a fixed position while the star is not being driven by pin 2 I, that is, during the interval the frame is in alignment with the aperture in position to be projected upon the screen I'I.

The action of the movement is as follows:

The cam carrying the master pin is continuously rotated as long as the projector is in motion, as will be more fully explained hereinafter. During the major portion of the operating time the star is maintained motionless, by virtue of contact between one of its four curved surfaces 24, and the adjacent surface of the cam ring 22. Under this condition it is evident the star cannot be rotated. It must, in fact, remain perfectly still until the two surfaces are released. In this condition theA movement is said to be on the lock. Remembering that the cam rotates continuously in the direction indicated by the arrow, it is evident that presently the' pin will engage one of the slots 25 in the star and, at that instant, surface 24 will be out of contact with ring 22 and free to rotate under the control of pin 2 I.

As the pin enters one of the star slots 24 it moves the star one-quarter of a revolution. The movement i-s very rapid but, nevertheless, movement of the star and the associated sprocket are initiated slowly, the speed gradually being increased to maximum. The star and sprocket then slow, gradually, to a full stop, whereupon surface 24 and ring 22 re-engage, locking the star. 'I'he picture is projected and the cycle of action is repeated.

In particular accordance with the present invention, the intermittent movement is driven at the rate of twenty-four revolutions per second with alternate, or odd revolutions, of shorter duration than the even ones. As stated heretofore, television cameras are designed to scan sixty fields per second and, therefore, in my apparatus the faster revolutions are preferably of twosixtieths of a second duration, while the slower revolutions are of three-sixtieths of a second duration. Thus it is seen that of the twentyfour frames scanned by the camera, twelve are scanned twiceror ,for two-sixtieths of a second each, which equals twenty-four-sixtieths of a second, while the remaining twelve are each scanned three times, or for three-sixtieths of a second each, which equals thirty-six-sixtieths of a second. From these ngures it is obvious that for each second of time twenty-four motion picture frames, which is 'the standard practice in motion picture art, are scanned sixty times, which is in accordance with television practice.

It is now evident that the different operating speeds normal to each of these arts may be thus correlated, by properly modulating the velocity of the shafting which drives the intermittent movement. j

Means for driving the intermittent movement in the desired manner is provided by the associated mechanism illustrated in the drawing and now to be described.

With reference to Figures l and 2, a motor 30 is provided for driving a shaft 3l which extends through a gear box 32 and has attached to its free end the usual shutter 33 provided with a pair oi'

opposed apertures

34 and 35. Also attached to the shaft 3l, on the portion within the gear box, is a worm 35 adapted to rotate an associated pinion gear 31 mounted on a shaft 38. Shaft 3l extends transversely through a bearing block 38 and has a disk 40 attached to its other end.

Disk 40 is provided with atransverse slot 4i into which one end of a pin 42 (which is secured to the side wall of a gear 43) is adapted to nt for transverse kslidable movement therein. Gear 43 is journalled in another bearing block 44 at a point onset from axial alignment with shaft 33, as shown at 45 (Figure 2) by the extended parallel lines 43 and 4l passing through the centers of disk 40 and gear 43. By reason 'of this onset of the centers of rotation of disk 40 and gear 43, when the disk is rotating, the angular velocity of the gearis modulated as described heretofore. In other words, for each revolution of disk 40, at a. constant speed, gear 43 will rotate through substantially one-half revolution at a speed greater than that of the following half.

Mounted adjacent one end of a shaft 50, and intermeshed with gear 43, is a gear 5l having a diameter equal to one-half the diameter of gear 43 and providing a resultant two-to-one ratio between the driving and driven shafts. For each complete revolution of gear 43, gear 5| will revolve twice and, as the speed of rotation of gear 43 has been velocity-modulated as described, gear 5l will move through one of its two revolutions at a greater velocity than will obtain during the succeeding revolution.

Shaft 50 passes through a bearing 52 on housing Il and into the interior of the intermittent movement I1. A gear 53 is attached to the end o! the shaft and is intermeshed with a similar gear 54 to which is secured the intermittent cam 25. A shaft 55, upon which gear 54 and cam 20 are mounted for rotational movements, is also joui-nailed in bearing 52.

It will now be clearly understood that shaft 50, and consequently gear 53 attached thereto, are being driven with modulated velocity, the duration of successive revolutions alternating between two-sixtieths and three-sixtieths of a second. The intermittent movement is, of course, driven correspondingly, through gear 54 to which the cam 20 is attached. Thus the desired variation in interval between successive pull-down actua- A anmactions is achieved in a novel and advantageousv the present invention provides a simplified, efii-` cient and improved motion picture projector in which standard intermittent movements may be advantageously employed.

As employed herein, the words standard intermittent movement are intended to denote A those types commonly employed in motion picture projectors and normally constructed and arranged to effect nlm pull-down at equal time intervals. Both the Geneva movement and the so-called unmodined Powers movement, I

referred to hereinabove, are exemplary of the class of devices covered by the term. I

It should be borne in mind that while the velocity variation, or modulation, of the present invention enables the use of standard unmodiiied intermittent movements, and is therefore advantageous; in a broader aspectthe modulation l taught is not limited in applicability to use with such movements only. However, it will be understood that such applications of the invention and modifications therein are contemplated, as may come within the termsl of the appended claims.

I claim: j

1. In a motion picture projector, film advancing means, and actuating means for operating said nlm advancing meansso as intermittently to move successive nlm frames into position for projection, said actuating means including: a continuously rotating member, an element discontinuously rotated thereby, velocity modulating means for causing successive complete revolutions of said continuously rotating member to occur at faster and slower rates, alternately, whereby correspondingly to vary the time interval between successive discontinuous rotations of said element, and means drivingly interconnecting said discontinuously rotated element and said nlm advancing means to effect movement of successive frames into position for projection after intervals of greater and less duration.

2. In a motion picture projector, film advancing means, and actuating means for operating said nlm advancing means so as intermittently to move successive nlm frames into position for projection, said actuating means including: a continuously rotating member. an element discontinuously actuated thereby once for each revolution of said continuously rotating member, velocity modulating means for causing successive complete revolutions of said continuously rotating member to occur at faster and slower rates, alternately, whereby correspondingly to vary the time interval between successive discontinuous actuations of said element, and means drivingly interconnecting said discontinuously actuated element and said nlm advancing means to effect movement of successive frames into position for projection after intervals of greater and lesser duration.

3. A construction in accordance with claim 1 and further characterized in that the successive complete revolutions of said continuously rotating member are completed in time increments alternating between two-sixtieths and threesixtieths of a second.

ananas 4. In 'a motion picture projector for use in television broadcast systems, 111m pull-down means, an intermittent movement coupled to said fllm pull-down means and eective to operate said means so as to move successive 111m frames intermittently into position to be projected for scanning, said movement including a continuously rotating element and a nim-actuating member discontinuously operated thereby upon completion of veach revolution oi said con tinuously rotating element, a substantially constant speed prime mover, and variable speed apparatus coupling said prime mover to said continuously rotating element and so driving said element that successive complete revolutions thereof occur at alternately greater and lesser velocities.

5. In a motion picture projector for use in television broadcast systems, film pull-down means, a Genevatype intermittent movement coupled to said lm pull-down means and effective to operate said means so as to move successive film frames intermittently into position to be projected for scanning, said movement in cluding a continuously rotating cam and aillmactuating star wheel discontinuously operated by `said cam upon completion of each revolution thereof, a substantially constant speed prime mover, and variable speed apparatus mechanically coupling sald prime mover to said cam and effective to drive said cam so that successive complete revolutions thereof occur at alternately greater and lesser velocities.

J. BINGIEY.

nEFanaNoEs CITED The following references are of record in the ille of this patent:

UNITED STATESv PATENTS