US2024609A

US2024609A - Sound picture system

Info

Publication number: US2024609A
Application number: US697902A
Authority: US
Inventors: Edwin H Smythe
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1933-11-14
Filing date: 1933-11-14
Publication date: 1935-12-17
Anticipated expiration: 1952-12-17

Description

Dec. 17, 1935.

E. H. SMYTHE SOUND PICTURE SYSTEM Filed Nov. 14, 1933 4 Sheets-Sheet l FIG.

INVENTOR EHSMYTHE B) I CH-Mudi' A TTORNEY Dec. 17, 1935. E. H. SMYTHE SOUND PICTURE SYSTEM Filed Nov. 14, 1953- 4 Sheets-Sheet 2 iiio inni Nu MK mu R a fist IN l/E NTOR BY HSMVTHE Dec. 17, 1935.

E. H. SMYTHE SOUND PICTURE SYSTEM Filed NOV. 14, 1953 4 Sheets-Sheet 5 FIG. 7

IINI/ENTOR E. HSMV THE A ORNEV 1935. E. H. SMYTHE scum) PICTURE SYSTEM Filed Nov. 14, 1933 4 Sheets-Sheet 4 FIG. 8

i atented Dec. l7, 1933 UNITED STATES PATENT OFFICE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application November 14, 1933, Serial No. 697,902

25 Claims.

This invention relates to sound picture systems, and more particularly to a method and apparatus for maintaining a constant and uniform velocity of movement of the sound record carrier relatively to the translating point.

In my copending application, Serial No. 697,901, filed Nov. 14, 1933, there is disclosed a photographic sound recording and reproducing system in which irregularities of the sound record movement due to the drive side and load side disturbances are compensated for, and relatively uniform movement of the sound record secured, by converting such irregularities of motion as are ordinarily communicated to the film into forces that operate upon the translating point and continuously shift its position longitudinally with respect to the direction of the film movement and in accordance with these irregularities of motion.

.The present invention has particularly to do with an improved method and apparatus whereby the velocity variations in the movement of the sound record or film are converted into corresponding electric currents by the coaction of a uniformly moving part of a reference system with another part which moves with the film or sound record, and which therefore contains in its movement the velocity irregularity components that have been superposed upon the film by the drive and load side velocity-varying forces. The uniformly moving part of the reference system has a uniform velocity which is the same as the average velocity of the part which is operatively associated with the film. As long as the film moves at a uniform velocity, without superposed variations, there is no relative movement as between the uniformly moving part of the reference system and the element or part that has operative association with the film. But any instantaneous velocity variation that occurs in the film movement is reflected in a corresponding relative displacement between the uniformly moving part of the reference system and the. film controlled element; and this relative displacement is converted in the preferred embodiments of the invention herein disclosed, into corresponding electric currents. These currents are utilized to shift the position of the translating point in such a way as to compensate for the corresponding irregularities of film movement, thus ensuring a relatively uniform movement of the film with respect to the translating point. v

In one of the preferred embodiments of the invention herein disclosed, the compensating currents are produced by the movement of a coil of wire in the strong annular magnetic field of a pertrolled element.

manent magnet carried upon the uniformly moving element of the reference system. In another embodiment of the invention herein disclosed a series of apertures in the element that moves with the film is arranged in a partially obscuring rela- 5 tion with a corresponding series of apertures in an element of the uniformly rotating reference system, and the light that passes through these apertures, varying in proportion to the degree of obscuration of one set of apertures with respect to the other, controls the voltage output of a light sensitive cell in accordance with the instantaneous velocity variations of the film controlled element. Other modifications embodying the principles of the invention, which are not herein specifically disclosed, may include the variation of the magnetic flux through a coil surrounding an armature the positional relationship of which with respect to the field of a permanent magnet carried on the uniformly moving part of the reference system is varied by the mechanical connection of the armature with the film controlled element; also an arrangement wherein the resistance of a variable resistance element is varied in accordance with the changes of positional relationship between the uniformly moving element of the reference system and the film con- 7 The foregoing are merely typical of some of the modifications that are possible within the broad principle of the invention herein disclosed.

A further feature of the invention involves the employment of a transformer having axially concentric windings one of which is stationary and the other rotatable, for the purpose of communicating to the compensatingcircuit, without the use of slip rings, the varying currentsgenerated by the relative movement of the elements carried by the rotating parts.

The invention will be more scribed in connection with the ings, in which:

Fig. 1 represents schematically the mechanical and electrical arrangement of a photographic particularly deappended drawsound record reproducer embodying the principles 2 whereby the velocity variations of the sound sprocket are converted into corresponding elec'- tric currents by means of a reference system including a coil moving in an annular magnetic field, the currents being carried by means of a rotating transformer winding to the compensating circuit;

Fig. 5 is a perspective view of an arrangement whereby the velocity variations of the sound sprocket are converted into corresponding electric currents or voltages by means of a reference system comprising two series of partially registering apertures that control the amount of light transmitted to a light sensitive element;

Fig. 6 is a diagram illustrating a circuit which may be used for connecting the moving coil or coils of the reference system with the compensating light valve;

Fig. '7 is a diagram illustrating a modified form of circuit connection; and

Figs. 8, 9 and 10 illustrate other forms of reference systems operating by the translation of velocity variations into electric variations through the medium of light.

Referring to Fig. 1, the photographic film 2| bearing the sound record is moved past the translating point 22 by means of a sound sprocket 23. The sound sprocket 23 is driven at an approximately uniform velocity by any suitable driving mechanism such as is customarily employed in talking motion picture systems. But the usual elaborate precautions employed to prevent any slight departure from absolutely uniform motion are in this case unnecessary.

On the same shaft with the sound sprocket 23 is an arm 24 carrying a member 25 which coacts with another member 25 to generate electromotive forces that instantaneously vary in exact accordance with the instantaneous variations of velocity of the sound sprocket 23 and the film which it moves past the translating point. In the present instance the member 25 is diagrammatically represented as a coil adapted to move in the annular magnetic field of a permanent magnet 26 carried upon a rotating member 21. The member 2'! merely rotates idly as a reference member, being driven from the sprocket shaft by the arm 24 through the medium of the pair of damped coiled springs 23. The moment of inertia of the reference member 21 and the elasticity and damping of the coils 28 are so proportioned as to give the combination a natural resonance below the lowest disturbing frequency for which it is desired to compensate. The reference member 21 and the magnet 26 that it carries therefore have a uniform rate of rotation which is equal to the average rate of rotation of the sprocket 23 and its driving shaft. But any instantaneous variation in the rate of rotation of thesprocket 23 and its shaft causes the coil 25 to move in the annular field of the magnet 26 and generate a corresponding electric current flow. This current flow, after transformation, correction with respect to phase and amplitude, and, if desired, amplification in the device 29, is applied to the ribbons 30 of a light valve, which ribbons are caused to move, as will hereinafter be described, to cause a shift of the line of light at the translating point 22 corresponding in phase and amplitude with the velocity variations of the film.

The translating line of light on the film is produced by the filament of the exciting lamp 3| the light from which is concentrated by the condensing lens 32 upon the slit between the light valve ribbons 30. The image of the brightly illuminated slit is focused upon the sound track of the film 2| at the translating point 22 by the objective lens 33. The light passes through the film, varied in intensity according to the photographic sound record on the sound track, falls upon a photoelectric cell 34 and is converted by the photoelectric cell and its associated apparatus, in the usual manner, into corresponding electric current variations for the operation of a telephonic loud speaker.

Referring to Fig. 2, this figure illustrates diagrammatically a photographic sound recording system in which velocity variations in the movement of the film are compensated for by a corresponding shift in the position of the line of recording light on the sound track of the film. Light from the exciting lamp 35 is concentrated by means of the condensing lens 36 upon the slit between the two ribbons 31 of a light valve, which ribbons are caused to approach and recede from each other in accordance with the sound modulated electric currents that flow through them. The light that passes through this brightly illuminated sound-current-controlled slit, after passing through the lens 38, and being reflected from the mirror 39 of the oscillograph 40, produces an image of the light slit at point 4!. image, in the form of a brightly defined narrow line of light the thickness of which varies in accordance with the movement of the ribbons 3'! of the light valve, is brought to a focus upon the sound track of the film 42 at the translating point 43 by means of the objective lens 44. The oscillograph 43 may be generally of the type which is illustrated and described in the paper by Dimmick, published in Vol. XV, No. 4, October, 1930 of the Journal of the Society of Motion Picture Engineers. As schematically illustrated, the support of the oscillograph mirror 39, pivoted on a knife-edge, is connected by light tension ribbons to opposite extremities of an armature pivotally balanced between the poles of a permanent magnet, the movement of the armature being brought about by an energizing coil which surrounds it.

As illustrated, the currents for tilting the oscillograph mirror and effecting the compensating shift of the recording line of light at the translating point 43 are generated, as in the case of the system of Fig. l, by a moving coil 45 carried on an arm 46 of the sound sprocket shaft coacting with the annular field created by the permanent magnet 41 carried upon the uniformly rotating member 48 of the reference system. The member 48 is driven through the medium of a pair of damped springs 49 which connect it with the arm 46 of the sound sprocket shaft. The variation from uniform velocity in the rotation of the sound sprocket shaft causes corresponding displacements between the moving coil 45 and the annular field of the magnet 41 of the uniform velocity member 48. The currents resulting from these displacements are transformed, corrected with respect to phase and amplitude, and, if necessary, amplified in the device 50 and passed through the energizing coil of the oscillograph 40. The tilting of the mirror 39 of the oscillograph causes a shifting of the line of recording light at the translating point 43 that corresponds exactly in phase and amplitude with the variation from uniform velocity in the movement of the film 42.

The light valve which effects the compensating movement of the line of light in the reproducing system illustratedin Fig. 1 may be generally of This the type disclosed in the article by Perreault, at page 412 of the Aug. 1932 issue of Bell Telephone LaboratoriesRecord, Vol. X, No. 12. Fig. 3 illus- .trates portions of the ribbons of such a light valve modified to adapt them for controlling the compensating shift of the line of light. In the form of light valve illustrated, although other dimensions than those given are suitable, it may be assumed that the ribbons and 52 are 2 inches long, 6 mils wide and mil thick, and that there is a 1 mil separation between their proximate edges. The aperture 53 for the passage of light between the exciting lamp and the sound track, may be assumed to be 120 mils long and 40 mils wide, so that the slit defined by the light valve ribbons is permitted an extreme amplitude of movement of approximately 40 mils before being obscured by the upper and lower edges of the aperture'53. With an optical leverage of 1:1 as between the slit and the film, this permits a corresponding extreme amplitude of compensating movement of the line of light on the film of approximately 40 mils. As the extent of linear displacement of the film at the translating point due to superposed velocity variations ordinarily does not exceed a very small fraction of an inch, even for the lowest periodicity disturbances, this amplitude of movement of the line of light on the film is sufficient for securing the compensating effect.

In order to completely close the aperture 53'for the passage of any light excepting thatwhich passes through the slit defined by proximate edges of the ribbons, an extremely thin and light shield 54 is fastened to the ribbons 5| and 52 so as to move with them. Along its center the shield 54 may be provided with a slit 55 enoughbroader than the slit between the proximate edges of the ribbons so that the light slit is defined by the edges of the ribbons and not by the edges of the slit in the shield. As the energizing current traverses the ribbons'of the compensating light valve in parallel, in order that the movement of both ribbons may be in the same direction, the shield 54 may be of metal, as mil thick duralumin, and may be in metallic conducting contact with the faces of the ribbons without affecting the response of the device to the actuating currents that flow through it. The relatively great length of the ribbons 5| and 52 as compared with their breadth reduces the stiffness factor and enables the valve to be tuned to a low resonance frequency (but one which lies safely above the highest disturbing frequency that needs to be compensated for), and therefore to be actuated by a relatively I small amount of electrical energy.

In Fig. 4 there is shown in perspective, with parts broken away, a reference system in which the velocity variations between the uniform velocity and the variable velocity members of the system are converted intocorresponding electric currents by meansof coils moving in annular magnet fields; and in which the electric currents generated in the movable coils are communicated to the external compensating circuit through the medium of a transformer one of the windings of which is stationary and the other of which is rotatable. Only as much of the structure is illustrated as is necessary to show the relationship between the various elements; and the illustration is largely a schematic rather than an exact mechanical representation of the structure.

The sound sprocket shaft 56, one of the bear-- ings of'which is shown at 51, carries on one end the sound sprocket 58 and on the other end the f? rotating element of the transformer 59. At an intermediate positionv on the shaft 56 are fixed two sets of radially extending arms 6!] andB l'. The sprocket shaft 58- is rotated by the driving shaft 62 through the medium of the beveled gears 63. 5 The reference system member 64 is arranged to rotate coaxially with the shaft 56, the member 64 either having a bearing upon the shaft. or if desired, having its bearing upon a stationary part of the frame of the machine. Rotary movement is imparted to the member 64 by the sprocket shaft 56 through the medium of the pair of arms 6!, at the outer end of each of which arms there is a connection with the. member 64 through the U medium of the damped coiled springs 55. Each of these coiled springs, clamped by felt in a well known manner, is connected at its inner end with the extremity of the associated arm Bl, outer end is adjustably connected with and at its a pin or post 66 set in the rotating member 5 3 of the refl erence system. Obviously the connection between the sprocket shaft 55 and the rotating reference member 64 may be made in any one of a variety of ways, the essential requirement being that the elasticity of the connection and its damping and the moment of inertia of the member 6 3 shall be such as to give the system a' natural resonance,

frequency below the lowest of the disturbing fre-.

' quencies that are to be compensated for, and that:

the resonance of the system shall have substan- 31}; tially critical damping. The maximum tude of relative displacement of the uniform, variable velocity elements of the reference systezai is determined by the stop pins 67, the c nnection of the damped springs 65 with their associated 35, i I

pins 66 being so adjusted that in normal operation the arms 51 shall lie midway their limit-\ ing stops 61.

At each end of the two tached a coil of wire 68 shown in the perspective are adapted to move in tween the poles of the two permanent magnets 69. The magnets are carried upon and rigidly fastened to the reference system member 64 by means of the bolts 78. The arms that carry the moving coil 68 are light, but rigid with respect to frequencies within the range of velocity variation frequencies that are to be communicated to the coils that they carry.

The moving coils B3 are electrically joined together in aiding relation and are connected with the inner or rotating winding H of the transformer 59. The outer or stationary transformer winding "[2 is connected, as has been described,55 with the compensating circuit that includes the light valve or oscillograph.

The transformer 59 may form a unit adapted to be slipped onto the protruding end of the sound sprocket shaft 56. In the embodiment illustrated in Fig. 4, the transformer includes an inner sleeve 13 and an outer shell M, preferably of material of high magnetic permeability, such as permalloy. The inner or rotating winding TI is carried upon the inner sleeve '23, and the outer or stationary winding is secured upon the inner surface of the outer shell 74. To complete the magnetic circuit of the transformer there .are two pairs of discs or washers, laminated, if desired, and of high magnetic permeability, at the 70 ends of the windings H and 72. The pair fits arms 66 is rigidly: at; (only one of which is drawing), which coils the annular fields betightly upon the inner sleeve 73 and clears the of the outer shell 15 and clears the outer surface 75 I faces are as close together as possible consistent with clearance, say, a 5 mil separation. In this] way the reluctance of the magnetic circuit is reduced and the leakage flux kept low.

To properly hold the parts of the transformer in rotatable but substantially unvarying relation with each other, the ball-bearings 11 and 18 are employed, the outer peripheryof each bearing being secured to the shell 14 and the inner periphery'being secured to the sleeve 13. As the magnetic circuit of the transformer is provided for by the sets of discs and washers 15 and 18, it is substantially independent of the path by way of the ball-bearings 11 and 18. A transformer thus constructed is adapted to transmit with only slight loss the velocity variation currents generated by the moving coils 68 of the reference system. These velocityvariation currents may have frequencies that lie within the range of from 1 to 100 cycles per second.

The connection of the moving coil or coils of the reference system with the compensating light valve ribbons may be in the manner shown diagrammatically in Fig. 6 of the drawings. The moving coil 98 has connection with the rotating primary winding H of the transformer 59; and

' the stationary secondary winding 12 of thetransformer is connected with the light valve ribbons 30, the connection including a reactance 19 to introduce the necessary amplitude correction. 'I'hetransformer windings H and 12 are preferably of high impedance, with many turns, and the coil 19 preferably has a reactance impedance greater than the impedance. of the light valve 38 and less than the reactive impedance of the associated transformer winding. Of course, the transformer 59 may, if desired, be so constructed that the required reactance in the light valve circuit may be due entirely to the leakage reactance of the transformer.

The circuit shown in Fig. 6 is upon the assumption that the electrical energy generated by the movement of the coils 68 in the reference system is sufiicient without amplification to effect the desired magnitude of movement of the compensating light valve ribbons. But if it is desired to have more energy available for the movement of the compensating ribbons, an amplifier may be introduced as shown diagrammatically in Fig. '7. In this case the moving coil 68 of the reference system is connected with the rotating primary winding H of the transformer 59', and the stationary secondary winding 12 is connected with the input circuit of the amplifierBD. The output circuit of the amplifier includes the primary winding of a transformer 8| the secondary winding of which is included with a reactance coil 82 in the energizing circuit of the compensating light valve 30. In this case the transformers 59 and 8! are wound to match the impedances into which they work, and the rotating transformer 59 is so constructed, as, for instance, by employing axially longer windings, that the reactance due to the leakage flux is reduced. As in the case of the circuit illustrated in Fig. 6, the reactance coil 82 may be dispensed with by deriving the required correcting reactance in the light valve circuit from the associated transformer by properly designing the transformer to that end. The design of such connecting circuits to secure the proper phase and amplitude relations between the interconnected elements is well understood in the art;

and the circuits of .Figs. 6 and 7, with appropriate changes in their electrical contents, may be employed for supplying the :velocity variation currents of the reference system to a compensating oscillograph, instead of to the light valve as shown.

Inthe modification illustrated in Fig. 5 the conversion of velocity variations into corresponding electric current variations for the compensaif,-

ing control ofthe translating point is effected through the medium of light. As illustrated, the

soundsprocket shaft 83 carries the sound sprocket 84 at one end and at the other end has rigidly attached to ita light disc.85 to the periphery of which an open-ended drum or cylinder 86 .is secured, The sound sprocket shaft 83 is rotated by the driving shaft 81 through the medium of the beveled gears 88. Only one bearing 89 for the sprocket shaft is shown; but it will be understoodthat the shaft has such bearings as are necessary for its proper support. Fulcrumed either upon the shaft 83 as its bearing, or, if

desired, upon. a separate bearing carried by the frame of the machine, is a relatively heavy disc-shaped member or wheel 90. This member rotates idly upon its bearing and is driven by therotating shaft 83 throughthe medium of a pin or post. 9|. set into the disc 85. The post 9| extends through a slit 92in the member 90 and.

is connected at its free end, through the medium of the felt damped and adjustable springs 93, with the two posts! that are set into the face of the member 90. 7 Obviously the damped resilient con:

nection of the member 90 with the shaft 83 may be made in any one of a variety of ways, the idea beingmerely to connect it so that as a result of its moment of inertia coacting with the elasticity of the resilient connection 93, the combination shall have. a natural resonant frequency below,

the lowest disturbing frequency that is to be com-f pensated for, so that the rotating member 90 of the reference system shall have a uniform velocity of rotation, the damping of the resilient connection being suchas to provide critical damping for the system.

In order to translate displacements between the members and,90 due to velocity variations of the filmor sound sprocket into corresponding light variations, the member is provided with a cylinder or shell which rotates coaxially with but just clears the outer surface of the cylinder or shell 86 attached to the periphery of the member 85. Each of the

shells

86 and 95 is provided with a corresponding series of apertures that are preferably in the form of straight edged slits,

the slits 95 in one of the shells preferably being slightly longer than the slits 91 in the other shell so as to avoid any possible variation of the light passing through registering slits by longitudinal or axial displacement of the two members with respect to each other, The series of slits in each shell extends completely around its periphery.

Therotary adjustment of the two members 85 and 90 with respect to each other is such that in normal rotation the slits are displaced with respect to each other by an amount equal to half their breadth, so that each slit in the series carried by one ofthe members is half obscured'bya longitudinal wall of the corresponding slit in the other member. The breadth of each of the slits in theshells of the two members is equal to the maximum angular displacement of one member with respect to the other, so that the maximum displacement of the two members with respect to each otheras a resultof the greatest; velocity variations will be such as to produce a movement the limits of which will be the complete registration and opening of the slits on the one hand, and their complete closure on the other. Any

lesser amplitude of movement produces corresponding lesser variation in the area of the openings controlled by the slits.

The light system controlled by the series of slits in the peripheries of the

shells

89 and 95 comprises, in the modification illustrated, an exciting lamp 98 within the shell 89 and a light sensitive element preferably in the form of two caesium photoelectric cells 99 in an enclosed space into and concentrate it upon the photoelectric cells.

The reflecting enclosure I90 is supported upon the frame of the machine in any convenient manner, and its open forward end is so arranged and proportioned as just to clear the outer surface of the rotating shell 95. The shell 95 may also carry a flange I I! I which serves to prevent the admission of any external light to the enclosure within the shell I90.

The exciting lamp 98 is mounted upon a fixture I92 carried by the enclosing shell I 09 and extending axially thereof. The forward end of the fixture and the lamp clear the edges of a circular opening I 93 in the wall of the shell 85, and a flange I99 is secured to the fixture I92 so as to overlap the opening I93 and prevent any direct passage of light from the enclosure within the shell 86 into the space enclosed by the reflecting shell I99. Supports for the photoelectriccells 99 are carried at the base of the fixture I02, and the necessary wiring for the exciting lamp 98 and the photoelectric cells 99 may be carried out through the fixture and connected with the external circuits. The reflecting shell I09 with its attached fixture I02 carrying the exciting lamp 98 and the photoelectric cells 99 are so mounted upon the frame of the machine that it and the parts that it carries may be withdrawn axially to permit access to the various elements. The photoelectric cells 99 are so mounted that their light sensitive surfaces are directed radially outward.

The maximum light available for the variable excitation of the photoelectric cells 99 may be increased by increasing the number of slits in the corresponding series in each of the

shells

86 and 95, the number being limited only by the requirement that the breadth of the wall between adjoining slits shall not be less than the slit breadth. With slits and intervening walls thus related, the maximum amount of variable light which is capable of passing through into the interior of the reflecting enclosure I09 when the slits are in registration is equal to half of the light that falls upon an annulus on the interior surface of the shell 86 having a breadth equal to the length of the registering portions of the slits. If desired, in order to increase the current output produced by the light that passes through the slits, the caesium photoelectric cells 99 may be replaced by photronic cells or selenium photo E. M. F; cells of the type described by Bergmann V in the Physikalische Zeitschrift, Vol. 32, N0. 7, April 1, 1931, pages 286-288.

To eliminate the effect of slight spacing irregularities in cutting the slits in the

shells

89 and 95, each pair of registering slits in the two shells 5;; may be cut in a. single operation; and then, in assembling them with the associated members 85 and 90 of the reference system, the shells may be maintained in the same relation with respect to each other as that which they occupied 1 ;v when they were out. In order that the limiting displacements of one member of the reference system with respect to the other shall not be exceeded, the members are provided with properly spaced and preferably adjustable limit stops. 155.1

The controlling elements of a modified form of reference system operating on the principle of translating velocity variations into light variations is illustrated in Figs. 3 and 9. The exciting lamp I95 is placed at the principal focus of the 20.1.:

lens I96 so as to project a parallel beam of light through the apertures controlled by the shutters III! and I98. The light which passes through the apertures in the shutters may fall directly upon the photoelectric cell I99, or, as shown, 25:.

may pass through another lens IIU which changes the direction of the light rays so as to cause them to be projected at any desired angle onto the photoelectric cell.

The shutters I91 and I98 are exactly similar, 30."

and may be of the form shown in Fig. 9. In the form here shown, the openings for the passage of light are approximately 15 sector-shaped apertures III separated from each other by 15 opaque walls II2', Under normal operating con- 35...

ditions each sector-shaped aperture of one shutter is approximately one-half obscured by the corresponding sector-shaped wall of the other shutter. Therefore, a 7 angular shift of the shutters with respect to each other in one direc- 4.0;.

tion causes a complete opening .of all the apertures and a l angular shift in the other direction causes a complete closure of the apertures. The elements H3 and II4 at the juxtaposed ends of which the shutters I9? and I98 are mounted, may be tubes or hollow shafts, one of which is an operative part of the variable velocity part of the reference system and the other of which is an operative part of the uniformyelocity part of the system. Therefore, any velocity variation in one of the elements with relation to the other causes a corresponding variation of the light which the shutters control, and a corresponding variation in the voltage output of the photoelectric cell. This variable output may be utilized to control the light valve, as alreadydescribed, or to control an electro-responsive device for regulating the operation of the associated mechanical system. It will be understood, or course, that the system schematically illustrated in Figs. 8 and 9 is so organized that the only light which falls upon the photoelectric cell I 99 is that which passes through and is controlled by the shutters I91 and I98 of'the reference system. In the modification illustrated in Fig. 10, the

- light which is projected from the exciting lamp ME A I by one opening and. one closure in the reference system cylinders, or an even multiple thereof. In the present instance, the arc subtended by the shield opening H9 is equal to that subtended by two sets of openings and closures in the reference system.

If the length of the slit I I9 were slightly shorter than it should be the forward one of the two beams of light indicated in Fig. 10 would be com- ,pletely cut off at one end of the slit before the following beam had started to pass through at the other end of the slit; and if the slit I [9 were slightly longer than it should be, the following light beam would start to enter at one end of the slit before the forward light beam had been completely out off at the other end of theslit. In either case there would be a slight variation in the output of the photoelectric cell that would not represent rotational velocity variations between the two members H1 and H8 of the reference system. This is prevented by an accurate adjustment with respect to each other of the slit H9 of shield lzil'and the angular spacing and dimensions of the slits and separating'walls of the two rotating members H1 and H8. The exciting lamp H5 has a straight filament that is arranged at the axis of rotation of the rotating system. As shown in Fig. 10, the beams of light, after passing through the slits and the aperture in the shield I20, are directed to the photoelectric cell H6 by the lens l2| in the lens tube I22.

An obvious modification of the arrangement illustrated in Fig. 10 is to'permit the perforations in one side of the sound record film, as the sound track on the other side passes the translating point, to serve as the element H! of the reference system, the region around and between the film perforations being photographically' blackened. Any shift in the position of the perforations with respect to the corresponding perforations in the uniformly rotating member H8 of the reference system, as a result of velocity variations in the movement of the film, causes corresponding variations in the transmitted light and corresponding variations in the photoelectric cell output.

Where the translation of the velocity variations into electric current variations is effected through the medium of light and as photoelectric cell, as in Figs. 5, 8, 9 and 10, the photoelectric cell is connected in the usual manner with an amplifier, and the output of the amplifier passes to the light valve or like'device through a correcting circuit the constants of which are so chosen as to deliver the compensating current to the light valve in proper phase and amplitude.

What is claimed is:

1. The method of compensating for velocity variations created by momentary deviations from uniformity of a sustained velocity of a sound record film past its translating point, which consistsin generating electric currents corresponding in relative strength to the amplitudes of velocity variations between a part associated and moving at the same velocities as the film and a part moving at a sustained uniform velocity equal to the average velocity of the film, and utilizing said currents to produce a compensating adjustment to obtain a uniform velocity relation between the film and its translating point.

2. The method of compensating for velocity variations createdby momentary deviations from uniformity of a sustained velocity of a sound record past its translating-point, which consists in moving a part associated with the record in the proximity of a part moving uniformly at a velocity equal to theaverage velocity of the first part, converting the velocity variations between the two parts into electric currents, and utilizing 5 said currents to produce a compensating adjustment of the translating point.

3. The method of controlling velocity variations created by momentary deviations from uniformity of a sustained velocity which consists in moving a part associated with a controlled member in the proximity of a uniformly moving part associated with a controlling member, converting variations in the relative velocity of movement of said parts into corresponding electric currents, and utilizing said currents to govern the relative velocity' of movement of the controlled member.

4. The method of controlling velocity variations created by momentary deviations from uniformity of a sustained velocity which consists in moving 20 a part associated with a controlled member in the proximity of a uniformly moving part associated with a controlling member, converting variations in the relative velocities of movement of said parts into corresponding light variations, translating said light variations into correspondingly varying electric currents, and utilizing said currents to govern the relative velocity of movement of the controlled member.

5. A compensating system for velocity variations created by momentary deviations from uniformity of a sustained velocity of a sound record, including a reference system having one element associated and moving with the sound record and another element moving at a uniform velocity equal to the average velocity of said first element, and means for converting velocity variations bea tween said elements into correspondingly varying forces and applying said forces to compensate for velocity variations in the movement of said sound record.

6. A compensating system for velocity variations created by momentary deviations from uniformity of a sustained velocity of a photographic sound record film, including a reference system having one element associated and moving with the film and another element moving at a uniform velocity equal to the average velocity of said first element, means for converting velocity variations between said elements due to irregularities in the movement of the film into correspondingly varying forces, and means for utilizing said forces to compensate for said film movement irregularities.

'7. In a sound picture apparatus employing a photographic sound record film, sound translating mechanism including a device adapted to effect a compensating movement between the translating line of light and the record film to compensate for velocity variations created by momentary deviations from uniformity of a sustained velocity, an element moving with the film, an element having a sustained uniform velocity of movement equal to the average velocity of movement of said first element, and means responsive to velocity 65' movement equal to the average velocity of the record carrier movement, and means adapted to convert velocity variations in the relative movement of said elements into correspondingrelectric currents and apply the same to said device to cause said compensating movement.

9. A controlsystem for sound picture apparatus, including a member associated and moving with a sound record, a member moving at a uni- 1Q form velocity equal to the average velocity of said first member, an electromagnetic system having an element set in motion by the relative movemember, an electromagnetic system having one element carried by one of said members and an- 25 other element carried by the other of said members arranged to generate electric currents commensurate with the amplitudes of velocity variations, and means for utilizing for velocity control the currents generated by the relative movements 3 of said members.

11. A velocity control reference system, including a member adapted to rotate at a variable velocity, a member rotated at a sustained uniform velocity equal to the average velocity of said first member, means for producing a magnetic field carried upon one of said members for producing electric currents commensurate with the amplitude of velocity variations, a conductor carried 'by the other member lying in said magnetic field and adapted to cut the same as a result of relative movement between said members, and velocity control means adapted to be actuated by the electric currents thus produced.

12. A velocity control reference system including a member adapted torotate at a variable velocity, a member rotated at a sustained uniform velocity equal to the average velocity of said first member, a permanent magnet having an annular field carried upon said uniform velocity member, a coil carried upon said variable velocity member and adapted to move in said annular magnetic field, and velocity control means adapted to be actuated by the electric currents produced by the movement of said coil in said annular magnetic field.

13. A velocity control reference system, including a member adapted to rotate at a variable velocity, a member rotated at a sustained uni- 60 form velocity equal togthe average velocity of said first member, an electromagnetic system carried ,upon and rotating with saidrotating members and adapted to generate electric currents corresponding to relative movements be- 5 tween saidmembers, and means operating by electromagnetic induction for converting the currents generated by said electromagnetic system into correspondingly varying electric currents in an external electric circuit.

70 14. A transfer system for feeble alternating electric currentsincluding a rotating element in which said feeble currents are generated, a transformer having two coaxial windings one of which is rotatable with respect to the other on the l 75 common axis of the two windings, said rotatable other winding being connected with an external .circuit.

15. A velocity control reference system, includ- 5 ing a member adapted to rotate at a variable velocity, a member adapted to rotate at a uniform velocity equal to the average velocity of said first member, a source of light and a light responsive element, said members being provided with series of corresponding apertures adapted to be interposed in normally overlapping relation between said source of light and said light sensitive element in the rotation of said members to control the light in accordance with velocl9 ity variations between said members, and a controlling circuit connected with said light sensitive element. 7

16. In a sound picture apparatus employing a photographic sound record film, sound translat- 9 ing mechanism including a device adapted to effect a compensating movement between a translating line of light and the record film, an element moving with the film, an element having a uniform velocity of movement equal to the 1 average velocity of movement of said first element, each of said elements being provided with a corresponding series of light transmitting and light obscuring portions normally in partially obscuring relation with each other, a source of. light and a light sensitive element so arranged. that the passage of light from one to the other is controlled by the relation between the light transmitting and light obscuring portions of said .i members, and an operating connection between said light sensitive element and said compensating device. 4

17. A velocity control reference system, including a member adapted to rotate at a variable velocity, a member adapted to rotate at a uni-- form velocity equal to the average velocity of. said first member, two peripherally slotted telescoping cylinders having their peripheral slots normally in overlapping relation with respect to each other, each of said cylinders being carried."- upon and rotating with a different one of said. members, a source of light and a light sensitive element soarranged that the passage of light from one to the other is controlled by the varying overlap between the peripheral slots in said cylinders; and a controlling circuit connected with said light sensitive element.

18. The method of compensating for velocity variations in the movement of a sound record 5 film past a translating line of light, consisting in moving one electrical element at a uniform velocity and another electrical element at the velocity of the film, in associating the two elements in a manner to create rapid changes in 00 electrical current values responsive to relative motion as a result of variations in the second electrical element and in using said electrical currents to adjust the line of light in a manner to obtain a uniform velocity relationbetween the film sound record and the translating line of light.

' 19. The method of compensating for momentary velocityvariations of differing amplitudes in a sound record film as it moves past a translating line of light, consisting in moving one 'of the film, in associating the two elements in y a manner to create rapid changes in electrical current values responsive to the relative motion therebetween commensurate with the amplitude of film velocity variations andin using said electrical currents to move said line of light longitudinally of the film substantially the same distance as the film sound record is moved by velocity variations of different amplitudes.

20. In a sound picture apparatus employing a linear sound record carrier, means to control the uniform translation of sound comprising two elements operatively connected to a member which drives said sound record carrier, said elements being so connected to said member that momentary variations in uniformity of the velocity of the member create relative motion in one ele- 'ment with relation to the other substantially equivalent to the variation in velocity transmitted to the record carrier, means for producing varying forces corresponding to the extent of movement of one element with relation to the other uniformly proportional to the amplitude of the variations, and means for applying said forces to compensate for said momentary deviations in velocity of the sound record carrier.

21. In a sound picture apparatus employing a linear sound record carrier, sound translating mechanism including a device adapted to effect a compensating positional change of the translating lineof light with reference to the record carrier, control apparatus for said device comprising one element driven by a member directly in contact with said sound record carrier, and

one'elcment flexibly connected to said later memher, said elements being so associated with each other that momentary variations in the uniformity of the sustained velocity of the record carrier create relative motion in one element with relation to the other, means for producing varying forces corresponding to the extent of movement of one element with relation to the other uniformly proportional to the amplitude of the variations, and means for applying said forces to operate said device for altering the position of said line of light to obtain a uniform velocity relation between the translating line of light and the sound carrier.

-22. In a sound picture apparatus employing a photographic sound record film, sound translating mechanism including a device adapted to effect a compensating positional change of the translating light with reference to the film sound record, a velocity variation control system including two electrical elements operatively connected to a member which drives the film, said elements being so connected to said member that momentary variations in the uniformity of the sustained film velocity create relative motion in one ele- ,,,ment with relation to the other corresponding in extent to the amplitude of the velocity variations, to produce varying electrical currents corresponding in relative strength to the amplitude of said variations, and means for applying said currents for operating said device to effect a compensating driven by said mechanical transmission system in multiple with said member, said device comprising one element adapted to rotate at said uniform sustained velocity and another element adapted to rotate at said uniform sustained velocity with velocity variations created by said 15 driving member, a coupling excited by the relative motion of said elements for creating forces capable of work, a strip driven by said member with variations in velocity to the same extent as the member, a separate device cooperatively associated with said strip, and means for utilizing said forces for moving said separate device to the same extent as said strip.

24. A compensating system including a mechanical transmission system terminating in a 25 driving member rotated at a uniform sustained velocity with momentary deviations created by irregularities in applied torque in said mechanical transmission system, a velocity control device driven by said mechanical transmission system 30 in multiple with said member, said device comprising one'element adapted to rotate at said uniform sustained velocity and another element adapted to rotate at said uniform sustained velocity with velocity variations equivalent to those 9 in said driving member, creating an electromagnetic coupling excited by the relative motion of said elements for generating electric currents varying in strength with the amplitude of velocity variations, an induction coil rotated by said 40 driving member, and means for transmitting the electrical currents created by said coupling to said induction member for converting the currents generated by said electromagnetic coupling into corresponding varying electric currents of 5 increased strength for operating electrical apparatus in an external circuit.

25. A compensating system including a trans- ,fer system for feeble electric currents including an electromagnetic coupling excited by relative 50 motion of its members responsive to momentary variations in the sustained velocity of a prime mover for generating feeble electrical currents,

- a strip driven by said prime mover, a device operable for compensating for variations in the move- 55 ment of said strip, and an induction coil having a rotatable member operated by said prime mover and electrically connected to said coupling for converting the feeble currents generated by said coupling into correspondingly varying electrical currents of a strength to operate said compensating device. I EDWIN H. SMYTHE.