US1864560A - Synchronizing system - Google Patents

Description

June 28, 1932. T. A. SMITH SYNCHRONIZING SYSTEM Filed Nov. 50, 1928 Ill 75 AMPL,

% iNV ENTOR T. A. SM IT H AT ORNEY Patented June 28, 1932 UNITED STATES PATENT OFFICE THEODORE A. SMITH, OF RIDGEWOOD, NEW JERSEY, ASSIGNOR T RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE SYNCHRONIZING SYSTEM Application filed November 30, 1928. Serial No. 322,704.

The present invention relates to a method and apparatus for synchronizing moving bodies and, while particularly directed to television systems throughout, the following specification is applicable, in general, to a types of synchronizing.

However, for the purpose of conveniently describing the invention in one of its preferred embodiments I will hereinafter describe the system in its application to television transmitting and receiving systems, although, it is to be understood, that I may, should I so desire, put the same or equivalent system to different usages.

In general, practically all television transmitters and receivers, which have so far been used in the art to any extent, contain rotat ing devices which are used to break up the picture into small parts, which are then transmitted as wholes. Rotating devices of this general character may be either disks provided with holes arranged at equal distances along a spiral track about the disk or mirror drums for the purpose of directing the light in a manner similar to that of the spiral disks, or, may be, what has become known in the art as lens disks. In general, throughout this specification the term disk will be used to define all of the general types of rotating devices whichmay be used for the purpose of analyzing orscannin and then re roducin an ima e of'the transmitted picture.

If it is assumed that it is desirable to transmit television pictures at the rate of 24 pictures per second, which has come to be stand ard sound moving picture practice in order to clearly reproduce the higher register from the sound track; thetransmitter and receiver disks must then rotate at a speed of 24 revolutions per second, which is 1440 R. P. M.

It is obvious that it is most difficult to construct a motor of the ordinary type which will rotate at this speed and still maintain the necessary constancy to keep the received picture from moving or hunting. Furthermore, if the speed of transmission of the picture varies slightly from a constant speed this is apt to cause a shifting of the received picture and the need for continual framing adjustments, such as are undesired, is then mostprevalent.

Several different methods of synchronization for the purpose of synchronizing the receiving apparatus with the transmitter in television systems are in general use at resent. These systems may be summed up briefly by describing in a general way their operation. The most common system is to transmit pictures at the rate of pictures per second corresponding to a disk speed of 1200 R. P. M. and to use a synchronous motor at the receiver which operates from the same 60 cycle supply main as the transmitter. This method is satisfactory so long as there is no changing phase difference between the transmitter and receiver alternating current supply but this is not always the case. Furthermore, both the receiver and transmitter motors continually exhibit tendencies to hunt, and this action causes a wavering of the picture from side to side. At the present time, most large cities have several sources of power supply which are each of slightly different frequencies which would tend to make synchronization, according to this scheme, impossible. Other than this, the method does not readily adapt itself to the transmission of 24 pictures per second, which is so desirable in the art.

Another method which has been used to a considerable extent is to maintain a constant speed of rotation at the receiving end by the use of constant frequency generators operating a synchronous motor. Such devices used to generate constant frequencies include piezoelectric crystals, tuning forks, magnetostriction oscillators and the like. The complexity of these devices makes them rather impracticable and, furthermore, they are subject to changes of frequency with changes in temperature and, therefore, if used, a suitable temperature change compensating arrangement should also be provided.

Still another method which has been used in the art is the mechanical governor which, however, does not usually maintain the speed sufliciently uniform and is subject to hunting to a large degree.

that which drives. the transmitting motor.

This may be done, for example, by a separate transmitting channel which is obj ectionable because of the lack of available channels,

1 or, may be done by superimposing the synchronizing frequency on the television signal and this method requires an unusually good filter at the receiver. In either case the alternating voltage is amplified sufficiently to drive the main motor and this requires an unusually large amplifier.

It is, therefore, an object of my present invention to provide a system which will avoid the objectionable feature of the synchronizing arrangements above described and which will at the same time maintain a constant speed relationship between the moving elements at the transmitter and receiver.

Still another object of my invention is to provide an arrangement of the character to be hereinafter described which is free from the effects of temperature changes and in which the rotating elements for reproducing the picture at the receiver will not be driven mechanically from any synchronizing impulses.

Still another object of my invention is to provide an arrangement wherein a synchronous motor may supply a rotating field current to the drive motor used to turn a disk.

A further object of my invention is to convert an ordinary universal motor suitable for driving the disk into what is effectively a synchronous motor when proper speed is attained and to then drive the disk from the universal motor now converted into a synchronous torque motor.

Another object of my invention is to pro vide an arrangement wherein a synchronizing system is provided in which there is complete mechanical independence between the synchronizing impulses and the driving means for the rotational elements.

Still a further object of my invention is to provide a synchronizing device which will start itself automatically and a device in which the onlymanual adjustments required will be the initial framing of the picture so that respective points on the receiver disk may be accurately coordinated with correspon'ding points on the transmitter disk.

Another object of my invention is to arrange a drive system for disk and the like at the receiving station in such a manner that the synchronizing device electrically controls the speed of rotation of the disk and the use of unduly large amplifiers is avoided.

Other objects of my invention are to provide in a manner to be hereinafter described a synchronizing arrangement especially adapted for use in television transmitting and receiving systems which is relatively simple in its construction and arrangement of parts, an arran ement which is compact, durable, fool-proo conveniently set up, efficient in its use, and ideally suited to the objects for which it is developed.

Other and ancillary objects will, at once, suggest themselves to those skilled in the art to which the invention relates by a reading of the following specification and claims in connection with the accompanying drawing wherein:

Fig. 1 shows a schematic arrangement of one of the simplest forms of the apparatus;

Fig. 2 shows a schematic diagram of one form of complete apparatus; and,

Fig. 3 is a detailed wiring diagram of the schematic showing of Fig. 2.

Now making reference to the accompanying drawing the method herein described for synchronizing the moving elements at the receiver in a television system with corresponding elements at the transmitter consists in utilizing one of the component frequencies of the television signal as a synchronizing impulse. Such a frequency is the picture frequency, 24 cycles, for example, and another is the linefrequency of 1152 cycles, for example, assuming that each picture is formed from 48, lines. This alternating voltage exists in the television signal at the receiver and is amplified sufficiently to operate a very small synchronous motor which may be arranged to drive a commutator system. This commutator is then conveniently arranged to take the place of the commutator on an ordinary universal motor, that is, it may be arranged to determine the current distribution through the armature coils and thus force the universal motor to run at a perfectly definite speed and practically convert the universal motor into a synchronous motor. rangement the universal motor is large and sufiiciently powerful to drive the disk.

From another .aspect the arrangement which I have herein provided may be considered as a mechanical amplifier which permits a relatively low power amplifier to control the speed of a large motor.

It isusually assumed that the transmitterdisk in a television system rotates ata constant speed. However, this is not always the case and the arrangement to be hereinafter described, as has been set forth in the ob- According to this an jects of the invention, is especially suited to keep the receiver disk in synchronism and to frame the received picture automatically even in cases Where the speed of the transmitter disk changes to a slight degree.

Now making reference more particularly to the drawing which forms a part of my application and first to Fig. 1 thereof, the disk 1 is driven by means of a main motor 3 controlled by the synchronously operated commutator 5, which in turn is rotated from the rotating shaft of a small 24 or 1152 cycle synchronous motor 7, in accordance with the arrangement hereinbefore described. It is here advisable to state that the arrangement is not limited to a system in which the synchronous motor operates at either 24 or 1152 cycles, but these values have been merely illustrated as convenient values by which I may definitely describe my invention. However, suppose, for example, that 30 pictures were transmitted each second and that each picture was composed of 50 lines, for example, then in this case the synchronous motor 7 may operate at either 30 cycles or 1500 cycles or even any other harmonic of 30 cycles, and like values apply to other systems wherein different numbers of pictures per second are transmitted and different numbers of lines per picture are used, as will at once suggest themselves. l

The coupling device 9 mechanicallyconnects the motor 3 to the commutator 5 and the synchronous motor 7 until such a time as the coupling device will open. Preferably the coupling 9 is a centrifugal coupler and is arranged to open When the main motor shaft 11 turns at a speed of 1440 R. P. M., or faster, which speed corresponds to the proper speed of rotation of the disk member 1, assuming, as before, that 24 pictures per second are being transmitted.

First, let it be assumed, that the main motor 3 operates from direct current. In this case the operation of the arrangement conventionally illustrated by Fig. 1 may be described as follows. At rest, the shaft 11 of the main motor 3 is coupled to its commutator 5 and the synchronous motor 7 by means of the centrifugal coupling device 9. When voltage is applied to the main motor 3 by closing a line switch (not shown) the motor will operate as an ordinary universal motor and it will. accelerate rapidly until the speed of 1440 R. P. M. is reached. At this speed the centrifugal coupling or clutch 9, coupling the main motor shaft 11 with the shaft 13, on which the commutator 5 and the synchronous motor 7 are mounted, snaps open and mechanically disconnects the motor 3 from its commutator 5 and the synchronous motor 7. From this point on the synchronous motor 7 will rotate at a speed of 1440 R P. M. providing, of course, that a television signal is being received and this consta-nt speed rotation will, as will hereinafter appear, force the main motor 3 to rotate at a corresponding and synchronous speed.

As a matter 01 :onvenience it is preferable to construct the main motor 3 with a rotating field and stationary armature. The commutator will then be fixed and the brushes rotated which allows the wiring between the commutators and armatures to be fixed.

Now referring particularly to Fig. 3 and to Fig. 2 in so far as it conventionally illustrates the arrangement disclosed by Fig. 3 the main motor 3 is provided with the stationary armature winding 15 and the rotating field 17. In the case illustrated the motor 3 is of the ordinary shunt-wound type. The field current for the motor 3 is supplied to the rotor elements by means of the slip rings 19 and the armature current is supplied through the fixed commutator 21 having connections 23 connecting each segment 25 thereof with a portion of the armature winding, and by means of the rotating brushes 27 and the slip rings 29, connected similarly to the rings 19 with a power supply line 31, a rotating field is supplied through the Winding 15.

In a manner similar to that shown by Fig. 1 a coupling or clutch device 9, which is opened centrifugally, connects the main motor 3 with the small synchronous motor 7 and its associated elements. The large motor 3 in each case is arranged to'drive the scanning or analyzing or reproducing disk 1 provided with either holes or lenses 33 extending in a spiral path thereabouts.

The small synchronous motor 7 is supplied with the energy from the amplifying tube system 35 whose output is preferably coupled through a transformer 37 and fed through the line 39 to the synchronous motor. The amplifier 35 receives energy from the television amplifying system 41 supplied with energy from a radio receiver of any desired character (not shown) through the line 43. The output energy of tube 41 of the television amplifying system, including amplifying tubes 41 and 51, is directed to a filter system 45 which may be composed of shunt inductance and capacity and tuned, if desired, to 24 cycles so that the amplifier 35 will be supplied with input energy at a frequency of 24 cycles and will transfer energy to the synchronous motor at this rate.

It should here be noted that the 24 cycle note will predominate in the received signal inasmuch as the picture at the transmitter is being scanned at the rate of 24 times per second. It is well known according to a theorem, as developed by Fourrier, that in a case where there is a repetition occurring at a fixed and definite rate the rate of repetition produces a corresponding definitely ascertainable frequency. In this case, while, perhaps, the-object at the transmitter is moved slightly between successive scanning movements of the television disk located at the transmitter, the background of the picture will form a constantly reproduced portion of the picture which will produce a 24 cycle component.

Further than this, if desired, I may produce the 2 1 cycle note by providing at the transmitter a framing line which will be transmitted once for each scanning of the picture, and, in doing this, it is advisable to have a distinct shade contrast between the framing line and the picture tone.

In accordance with what is above disclosed, it is also possible to select from the 24 cycle frequency ascertainable at the'receiver, in accordance with the example illustrated, a harmonic of this frequency and, therefore, if desired, I may select the 48th harmonic to control the synchronous motor 7. This harmonic, in the case illustrated, if the picture is assumed to be composed of 48 lines, will be the 1152 cycle note previously defined. Also, in a similar manner, I may provide as a means for selecting or distinguishing the 1152 cycle note through a filtering arrangement, similar to that disclosed for filtering the 24 cycle note, a distinct framing line on the picture at the transmitter. This framing line will then be transmitted once for each path of scanning across the picture surface and, in a case where the line is repeated 48 times per picture and 24 pictures per second are transmitted, the 1152 cycle note is directly produced in accordance with the above named theorem.

The efiect of a framing line may be produced in several different ways :-for example; by actually holding a distinctively shaded frame around the picture; by cutting off a portion of the light around the edges of the picture with a mask; or even by external electrical means.

By each of these latter means for producing either the 24 cycle note, or, the 1152 cycle note, it is possible to obtain increased accuracy, in the frequency which controls the synchronous motor at the receiver although, it is to be understood, that satisfactory operation is also obtainable by directly selecting the 2 1 cycle note predominating according to the repetition of successive pictures, each of which are substantial duplicates of the preceding picture.

Also, as shown by Fig. 3 of the drawing, in particular, a neon glow lamp 47 is supplied with energy from the tube 51, forming a portion of the television amplifying system. This neon lamp 4? is arranged to produce a glow of an intensity proportional to the point for point intensity of light and shade in the picture at the transmitter and when the holes or lenses 33 in the disk 1 pass in front of the glow lamp the effect observed by looking at the disk is a reproduction of the point for point intensity of light and shade in the picture at the trans mitter. While the glow lamp, in the case shown by the conventional showing in Fig. 3, is not placed adjacent the disk member 1 this is merely done for convenience of illustration, and, it is to be assumed, that the lamp 1 The reason why the main motor will operate only at 1440 R. P. M. in accordance with the example cited may best be explained by noting the similarity between the action of the main motor 3 when operating in the man ner above described and the operation of a true synchronous motor. A true synchronous motor has a rotating field supplied by direct current, and, in the case illustrated, the motor 3 has this type of field also, of course, assuming that a direct current is used as above suggested. Further than this a synchronous motor has a stator element which, When fed with alternating current, produces the effect of rotating magnetic field and this same effect has been produced in this case by means of the commutator 21. The rotating field, of course, determines the speed of rotation of the motor and, therefore, the motor speed is entirely independent of the line volt age as long as the motor has sufficient torque to drive the load.

It is, therefore, seen that a system has been produced in which the operation is equivalent to starting a disk or other moving body in 1'0- tation by means of an ordinary universal motor, then bringing a synchronous motor up to speed by means of the universal motor, then mechanically disconnecting the universal motor from the synchronous motor, and finally utilizing the small synchronous motor to effectively change the universal motor into a large synchronous torque motor. It is to be understood that only a very small amount of energy is needed to drive the small synchronous motor used for turning the rotary brushes 27 and, therefore, excessive amplification of the synchronizing frequency energy is unnecessary.

So far, in this speci direct current has been considered. However, the system, as above described, will also function with the use of alternating current and the action in this case will be similar to that in the ordinary universal motor, and the speed of rotation is similarly governed by the externally driven commutator.

In an arrangement of this type it is essential that the small synchronous motor 7 run without the slightest amount of hunting and for the purpose of accomplishing this result I have provided a small inducion brake 49 mounted on the shaft of the small synchronous motor. Also to avoid hunting in the large motor used for driving the disk I have fication, only the use of provided a large number of armature poles so that it is not possible for the larger motor to hunt over a large number of degrees.

In an arrangement of this type horizontal framing of the received picture disk is readily accomplished by rotating the fixed commutator to a slight degree and vertical framing may be accomplished by breaking the main motor circuit rapidly, or, if it were not for the various electrical connections between the main motor and the commutator, this might be accomplished by rotating the com mutator a large amount so as to accurately position the picture vertically.

From the above description. it is evident that various improvements may be made to the arrangement disclosed without departing from the principle of operation and the spirit of invention as above set forth and I, therefore, expressly reserve the right to make such modifications within the system as may fall fairly within the spirit and scope of the invention as defined by the following claims:

I claim:

1. A synchronizing system including a large motor for driving a rotational element, a small synchronous motor, means for bringing the synchronous motor up to speed by said large motor, means for mechanically disconnecting said motors one from the other at a time when the desired speed is attained, means for supplying impulses to said small synchronous motor at a predetermined rate, and means associated with and controlled from said small synchronous motor for converting said large motor into a synchronous torque motor mechanically independent from said small synchronous motor for driving the said rotational element at a synchronous speed.

2. A synchronizing system for television including a motor for driving the rotational elements of the system, means for bringing the said motor up to a synchronous speed, a synchronous motor, a mechanical coupling connecting said first motor and said synchronous motor, means for mechanically disconnecting the two said motors at periods when the said first motor has reached a speed approximately corresponding to the said synchronous speed, and means provided from received signalling impulses for driving the said synchronous motor at a speed in synchronism with corresponding rotational elements of the transmitter, and means controlled by said synchronous motor for electrically controlling said first motor to maintain the same at a synchronous speed and phase relationship with respect to a transmitter at all periods. I

3. In a television synchronizing system, a universal motor for driving rotational ele ments, a synchronous motor mechanically connected with said universal motor, means provided by said universal motor for bringing the said synchronous motor up to a; desired speed, means for completely mechanically disconnecting the two said motors at periods when the desired speed is attained, and means provided by said synchronous motor for electrically driving said universal motor at synchronous speed and thereby converting the same into a synchronous torque motor.

4. In a synchronizing system, the combination of a. driving motor, a synchronous motor mechanically connected with said drive motor and arranged to be brought up to proper synchronous speed by said drive motor, means for completely mechanically disconnecting the said drive motor from said synchronous motor upon the attainment of the predetermined desired synchronous speed, means provided by received signal impulses for maintaining said synchronous motor in a. constant speed relationship with a trans mitt-ing system, and a commutator means for said drive motor connected with the rotary port-ion of said synchronous motor for continually supplying a rotary field to said drive motor and thereby converting the same into a second synchronous torque driving motor.

5. In a synchronizing system, the combination of a motor'for driving elements to be operated in synchronism, a synchronous m0- tor mechanically coupled with said drive motor, means provided by said drive motor for accelerating said synchronous motor to a desired synchronous speed, means for completely mechanically disconnecting the two said motors at periods when the said synchronous motor is operating at the desired speed, means for maintaining synchronous speed in said synchronous motor, and a commutator for said drive motor mounted on the rotary shaft of said synchronous motor and mechanically independent from said drive motor for continually supplying a rotary field current to said drive motor so as to convert the said drive motor into a synchronous torque motor for maintaining a gonstant rotational speed of said disk mem- 6. In a synchronizing system, a driving motor, a synchronous motor, means provided by said first named motor for bringing said synchronous motor up to a desired rotational speed, a centrifugal clutch connecting said drive and synchronous motors, said clutch being arranged to mechanically disconnect said motors at periods when the desired synchronous rotational speed in said synchronous motor is attained, means for supplying driving impulses to said synchronous motor at a predetermined rate, and commutating means for said drive motor associated with and controlled from said synchronous motor, whereby a. continuously rotating field current is supplied to said drive motor and the said drive motor 1s converted eeeeeo into a synchronous torque motor mechanically independent from said first named synchronous motor.

7. in a synchronizing system, a motor for driving rotating; elements, said driving motor having a stationary armature Winding, a synchronous motor, a. commutating system for said drive motor mechanically associated with said synchronous motor, electrical connections between the said stationary armature of said drive motor and the conducting segments of said commutator, means for passing electrical currents through said connections, means provided by said drive mo tor for accelerating said synchronous motor to a speed corresponding to the desired synchronous rotational speed of said driven rotary elements, a coupling for mechanically disconnecting the said drive motor from said commutator and the associated synchronous motor at periods when the desired rotational speed is attained in said synchronous motor, means for continually supplying driving impulses at a rate corresponding to the desired synchronous speed to said synchronous motor, and means provided by the said mechanically independent commutator for said drive motor driven at the desired synchronous speed by said synchronous motor for applying rotary field currents to said armature and converting the said drive motor into a synchronous torque motor for driving said rotational elements in synchronism with said synchronous motor.

'rrrnononn A. SMITH.

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