US2150239A - Synchronizing system - Google Patents

Description

March 14, 1939. H NICHOLS 2,150,239

SYNCHRONIZING SYSTEM Filed Dec. '7, 1954 2 Sheets-Sheet 1 y- P P INVENTOR Filed Dec. '7, 1954 2 Sheets-Sheet 2 INVENTOR Patented Mar. 14, 1939 UNITED STATES PATENT OFFICE SYNOHRONIZIN G SYSTEM Application December 7, 1934, Serial No. 756,486

Claims.

This invention relates to synchronizing systems and more particularly to the synchronization of periodic elements in visual communication systems. i

As is well known, the electrical transmission of intelligence for direct interpretation by the eye, whether in the form of writing, pictures, or images, involves a space-time relationship requiring the synchronization of periodic elements 10 at the sending and receiving ends of the transmission system, or some equivalent arrangement to accomplish the same results.

A general object of the invention is to provide methods, and suitable apparatus for carrying these methods into effect, which will enable synchronization of the controlled element of a visual communication system to be accomplished automatically and with a high degree of pre- ClSlOll.

A further object of the invention is to provide a synchronizing system in which the controlled element at the sending end of the system periodically transmits definite phase information to the receiving end of the system, there to utilize the received phase information to automatically establish synchronism of a controlled element with the controlling element, and thereafter to utilize the received phase information to maintain synchronism of the controlled element. A further object of the invention is to accomplish the automatic synchronization of any number of receiving instruments under the control of a single transmitting instrument, a condition highly desirable in mass visual communication systems.

A further object is to provide a system of synchronization in which the synchronizing signals are inherently of an order and nature consistent with the visual signals, and in which the transmission apparatus for the visual signals may be utilized to transmit the synchronizing signals without special adaptation to that end.

A further object of the invention is to accomplish automatic synchronization with relatively s mple and inexpensive apparatus, which apparatus will be easy to operate and easy to keep in order, and will be efiicient and reliable in action.

Other objects and features will be in part obvious, and in part hereinafter pointed out in connection with the following description, the accompanying drawings, and the appended claims.

It is the practice in certain types of picture transmitting systems to provide rotating relements at the transmitting and receiving stations which are required to move in synchronism for proper recording of the received picture. A rotating drum provides a convenient form upon which to mount the transmitted and received record of the visual matter, and such 5 commonly used arrangement will be used for 11- lustrative purposes. There is usually a blank portion of each drum which is not eifective in the transmission of impulses corresponding to the visual matter (briefly called the visual signals) 1c and as the drums are rotated, these blank portions are presented to the light source once during each revolution of the drum. The corresponding-portion of the revolution is commonly called the "underlap period, and it is during 5 this period that the periodic synchronizing Sig-- nals of the invention (briefly called synchronizing signals) are transmitted over' the transmission system.

Inaccordance with the present invention, an 20 arrangement is provided whereby synchronizing signals transmitted during the underlap period are employed to automatically establish synchronism of the controlled rotary element, and thereafter to maintain precise unison of the controlled element with the controlling element. Each synchronizing signal may occupy the entire underlap period, but preferably occupies only the middle portion of such period, thus facilitating the separation of the synchronizing and visu- 30 al signals. The synchronizing signals may be of the same character and amplitude as the visual signals, but preferably have some distinguishing feature. For various practical reasons, and particularly to avoid introducing cur- 35 rents of excessive magnitude which might produce objectionable eflfects in the transmission system, or in neighboring circuits, it is usually preferable to restrict the synchronizing signals to the same amplitude range as the visual sigp,

' of this particular form.

At the receiving station, the synchronizing signals may be employed to release the controlled 5o element from a definite phase position, thereby instantly to establish approximate synchronism, or the synchronizing signals and/or visual signals may be employed to gradually bring a continuously rotating controlled element into synchrop nism from any out-of-phase position Methods are shown for affecting synchronism by controlling the speed of the driving motor, by correcting the phase of the controlled element without change in the speed of the driving motor, and by controlling the frequency of the power supply to the driving motor.

The operation of the invention will be more clearly understood from a consideration of the following description, and of the drawings in which:

Fig. 1 shows one form of controlling element and synchronizing signal generator at a sending station.

Fig. 2 is similar to Fig. 1, but shows an alternative form of controlling element and synchronizing signal generator.

Fig. 3 is a diagram representing the synchronizing signals as related to the visual signals.

Fig. 4 shows one form of controlled element adapted to the receiving end of the system.

Figs. 5, 5a, and 5b, show three phases of the operation of the control arrangement at a receiving station.

Figs. 6 and 6a show a phase cox-rector mechanism adapted for use with the invention.

Fig. 7 shows schematically the control circuits for the phase corrector of Fig. 6.

Fig. 8 shows schematically a form of control arrangement adapted to effect synchronism by controlling the speed of the drive motor.

Fig. 9 shows schematically a novel form of control arrangement adapted to effect synchronism by controlling the frequency of the power applied to a driving motor of synchronous type.

Fig. 10 illustrates graphically the effect of the control arrangement of Fig. 9 upon the frequency of the driving impulses, and hence upon the speed of the synchronous motor.

In the several flgures, like characters indicate like parts.

While it has been chosen to illustrate the invention as applied to a system for transmitting pictures,- it is understood that the invention is applicable to any signalling system wherein synchronism is desired.

Referring to Fig. l, the rotary controlling element ill at the sending station is shown as a disc, but may be a drum, cylinder or any other form of periodically moving element. Light from a light source II is focused by a lens I! on the edge of disc Ill, as indicated. Disc I0 is provided at one point on its periphery with an inclined reflector or reflecting surface, such as notch Ilia. The bottom of the notch may be made highly reflecting by polishing, by mounting a small mirror thereon, or other preferred means. It is preferable that the other surfaces in the path of the light beam be rendered non-reflecting, as for example by covering with dead black paint.

At one point in each revolution of disc I0, light is passed from light source il toreflector Illa, and thence to photo-cell IS. A suitable mask (not shown) may be interposed between reflector Ila and photo-cell ii to restrict the light beam passing therebetween to desired size and proportions. Photo-cell ll may be an auxiliary photocell, as shown, or it may in some cases be the main photo-cell used for scanning the picture. The resistance of a photo-cell'varies in accordance with the light falling on its sensitive surface and hence the current in the circuit of cell it varies according to the illumination of its sensitive surface. This varying current is ampli- 75 fled by amplifier II, and sent to the line as indicated, or applied to modulate a carrier current in well known manner. Since reflector Ina comes into action only during the underlap period, there is nointerference with the visual signals. Further, since there are no contacts involved, difficulties which might arise from sparking, contact deterioration, inductive interference, etc. are entirely eliminated.

Referring now to Fig. 2, the same general arrangement of apparatus as in Fig. l is shown. Reflector Ilia is, however, mounted on the end of a drum or cylinder which serves as the mounting for the visual matter being scanned. Light source ll, instead of being steady, is of quick flashing type such as a neon lamp, and is flashed continuously at a high frequency, say 2000 times per second, by oscillator 15. Hence when the light link between source Ii and photo-cell i3 is completed by the intercession of reflector Ila, light variations of comparatively high frequency are received on the sensitive surface of photo-cell ll. These light variations produce corresponding current variations which are applied to amplifier I4 and are thereby suitably amplifled for transmission purposes. The advantage of the flashing light source is that a distinctive frequency characteristic is imparted to the synchronizing signal, and furthermore, the photo-ceil amplifiers commonly used in visual communication systems operate more efliciently when alternating variations are applied thereto.

Referring to Fig. 3, the visual signals are indicated by V, while the synchronizing signals are indicated by S and S. The single synchronizing impulse produced by the arrangement shown in Fig. 1 is indicated by 8, while the series of alternating impulses produced by the arrangement of Fig. 2 is indicated by 8. Both types of signals are comprehended by the term synchronizing signal.

It is to be noted that once during each revolution of the controlling element, at a flxed and sharply defined phase position, a synchronizing signal is generated and sent to the line in a form adapted to the transmission system. This synchronizing signal is sent during the underlap period indicated by the interval a, and is of a character consistent with the visual signals and its function at the receiver.

Referring now to Fig. 4, the controlled element is shown for illustrative purposes as a rotating disc 20, but as in the case of the controlling element, may be a drum, cylinder, or any other form of periodically moving element. Disc II is characterized by having two long arcuate light deflecting surfaces of different inclination, designated by 20b and 200, and a short, non-reflecting arc, preferably normal to the beam of the light link, which will be referred to as null arc Ila. For purposes of illustration, it will be assumed that are 20b, in cooperation with other control elements, will eflect a slowing down, or phaseretardation, of the controlled element, hence it will be referred to as retarding arc 20b. Likewise, it will be assumed that are 200 will effect a speeding up, or phase-advance, or the controlled element, hence it will be referred to as advancing are He. The advancing and retarding arcs preferably each occupy approximately a semi-circumference beginning at null are 200 and meeting in a line diametrically opposite are 200. This junction line will be termed the nadir line 20d. While the construction shown is preferred, other constructions may be employed to suit particular applications.

Referring now to Fig. 5, the synchronizing control arrangement, in addition to disc 20, comprises light source 2|, directive means such as lens 22 focusing the flash of 2| upon the edge of disc 20, photo-cells 23a and 23b, and amplifiers 24a and 24b associated therewith. The received synchronizing signal, received over any suitable apparatus, is amplified if necessary by amplifier 25 and is applied to light source 2 I, of quick-flashing type such as a neon lamp. The flash of lamp 2| should follow as closely as possible the duration of the synchronizing signal, so that the flashes will represent precisely the synchronizing signals as generated at the transmitter. The point of focus of lens22 marks the phase position which, for perfect unison, arc 20a should occupy when the synchronizing flash occurs, hence it is termed the unison point.

Assuming, by way of illustration, that synchronism exists, which condition is represented by Fig. 5, lamp 2| will flash periodically in unison with the synchronizing signal, but no effect is produced thereby on photo-cells 23a and 231) since null arc 20a is exactly opposite the unison point each time lamp 2| flashes. The flash of lamp 2| is partly absorbed and partly reflected back, as indicated, so that the amount of light reaching the photo-cells is negligible.

Referring now to Fig. 5a, it is assumed that null are 2011 has just passed the unison point when the synchronizing flash occurs. Such condition, assuming prior unison, would indicate that disc 28 has speeded up slightly, and is running ahead of unison. When the synchronizing flash occurs, the light beam is deflected by retarding are 201) to photo-cell 23a as indicated. Photo-cell 23a is thus energized, and by suitable amplifying means, indicated as amplifier 24a, energizes corrective means, presently to be described, and retards the motion of disc 20 thereby to restore unison.

Referring now to Fig. 5b, it is assumed that null arc 20a has not yet reached the unison point when the synchronizing flash occurs, hence advancing are 200 deflects the flash to photo-cell 23b, and thus causes the motion of disc 28 to be advanced thereby to restore unison.

Referring now to Fig. 7 which shows a preferred form of amplifier for use as amplifiers 24a, 24b of Fig. 5, each photo-cell 23a, 23b is as sociated with an electronic relay 30, 3|, as shown. A preferred form of electronic relay is a gaseous discharge tube of triode type having a cathode, anode, and grid, all in well known manner. Such types of discharge tubes are characterized by their practically instantaneous response and high amplification factor. The cathode of photocell 23a is connected to the grid of relay 30, and photo-cell 23b is connected in similar manner to relay 3|. The anodes of both photo-cells are connected to positive battery. Capacitors C, C are connected from cathode to grid of their respective electronic relays, as shown. Corrector magnets MI and M2 are connected in the anode-cathode circuit of their associated electronic relays.

When photo-cells 23a, 23b are dark, they are of very high resistance, hence the potentials on the grids of the associated electronic relays are substantially the same as their respective cathodes. Under these conditions, the electronic relays are held un-ionized, and the anode current is negligible. When either photo-cell is illumina ied, its resistance is greatly lowered, hence the potential of the grid to which it is connected is raised positively. This rise in potential of the grid of the electronic relay ionlzes or -trips same, causing a large increase of anode current and energizing Ml or M2, as the case may be. As is well known, the grid of a gaseous discharge tube normally can cause the tube to ionize, but is unable to de-ionize the tube. Hence means additional to the grid is required to terminate the discharge thru the tube. A device to terminate the discharge of either electronic relay is indicated by block 26, connected in the common anode circuit as shown. While any form of discharge terminating device may be employed, a preferred device is a timed cut-off relay such as that shown. Grid suppressor resistances R, RI serve to limit the grid current upon ionization, thus protecting the photo-cell and electronic relay from excessive currents.

Referring now to Fig. 6, which shows a preferred form of phase corrector mechanism. for use with the invention, drive motor 40 is provided with a reduction gear box 40a whereby the speed of drive shaft 4| is suitably reduced to drive ro-' tary cylinder 42 at a slower speed than the motor, as is usually found desirable. The record sheet upon which the visual matter is to be recorded is mounted on cylinder 42, strip 43 serving to hold the edges of the record sheet securely in place. Strip 43 may therefore be taken as representing the underlap period. Recording mechanism not shown serves to record the visual matter on the record sheet on the drum.

The phase correcting mechanism comprises corrector gear assembly 44 and the mechanism. of Fig. 6a. Referring now to the gear assembly, bevel gear 45 is fast on drive shaft 4|, while bevel gear 46, of similar pitch, is integral with sleeve 46a, thelatter being rotatable on drive shaft 4|. Drum 42 is mounted on a flange 2|! on the outer end of sleeve 46a. The edge of flange 20 is chamfered in the same manner as thatof disc 20 in Fig. 3, and functions in the same way. Bevel idler pinions 41, 41' are rotatablymounted inside ring gear 48 whose periphery is cut to form a' worm gear. Worm 49 engages the teeth of ring gear 48 for the purpose of rotating same. The light actuated, synchronizing control arrangement associated with flange 20 is the same as that described in connection with Fig. 5 and functions in the same way.

Referring now to Fig. 6a (which shows the actuating means for ring gear 48), on the shaft of worm 49 are mounted ratchet wheels 50, 50. Pawl 5|, when actuated by corrector magnet M|, engages ratchet wheel 50 and steps same in the direction indicated; in like manner, pawl 5|, when actuated by corrector magnet M2 steps ratchet wheel 50' in the opposite direction as indicated. Worm 49 transfers the rotary motion of. the ratchet wheels to ring gear 48. When ring gear 48 is rotated thru an angle of 11. degrees, bevel gear 46 will be rotated relatively to bevel gear 45 thru an angle of 2n degrees, and this action applies whether the gears are at rest or in motion.

Consider now the process of synchronizing drum 42 by means of received synchronizing signals, utilizing the apparatus shown in Figs. 6, 6a, and 7. Assume that drum 42 is in rotation, that lamp- 2| is flashed coincident with the received synchronizing signals, and that drum 42 is driven in substantial .isochronism with the controlling element at the sending station but is in advance of its proper phase position. Under these conditions, retarding arc 20b will receive the flash of lamp 2| and will deflect same to photo-cell 28a. Referring for the moment to Fig. '7, upon illumination, photo-cell Ila trips electronic relay II and a current discharge therethrough energizes corrector magnet Ml, the discharge being terminated after a predetermined interval by cutoif device 20. Upon being energized, Mi pulls in pawl I (see Fig. 60.) advancing ratchet wheel BI, and thru the medium of worm 40, ring gear 44 and idler gears 41, 41'. The arrangements are such that idler gears 41, 41' move in the direction of rbtation of the drive shaft, and drum 4! is retarded in phase. This process is repeated upon the reception of each synchronizing signal until arc 20a is brought to the unison point coincidentally with the flash. Thereafter, the phase angle of drum 4! is corrected as necessary to maintain unison.

Without further analysis, it will be clear that had it been assumed that drum 42 was lagging its proper phase position, advancing arc 20c would have been presented to the flash of lamp 2 i, and the corrector gear mechanism would have been actuated in the proper manner to advance the phase of drum 4! to establish unison. There after, phase corrections would be applied as necessary to maintain unison.

By having arcs 20b and 200 equal in length and extending around the entire circumference, except for the short null arc, drum 42 can be brought into unison from any out-of-phase position in the least number of steps possible under the circumstances. Since a sharp line of demarcation between arcs 20b and 200 is presented at the nadir point, stable operation at that point is impossible. Hence the null arc represents the only point at which unison can be established.

It is to be noted that the construction of disc 20, together with the parts of the system generating and utilizing the synchronizing signals, cooperate to cause actuation of the phase correcting mechanism upon a very slight departure of disc 20 from unison. Thus the invention makes it possible to maintain a high degree of precision in synchronization.

In the preceding analysis of the synchronizing procedure, it was assumed that the synchronizing signals alone were being received, or else that selective means of some kind, such as a filter, eflected a separation of synchronizing and visual signals, so that interference in their respective applications was averted. The invention is capable, however, of automatically establishing unison even tho the visual and synchronizing signals are differentiated only to the extent indicated in Fig. 3, that is, the signals are separated by a time margin. The analysis is as follows:--Cut-oflf relay ii is so timed that its operating cycle is slightly less than the period 'of the synchronizing signals. Hence upon being energized, its contacts are held open until just prior to the normal arrival of a succeeding synchronizing signal. Let it be assumed that with the controlled element rotating at synchronous speed, but out of phase, the synchronizing arrangement of Figs. 6 and '1 is made operative. If the first signal received is a synchronizing signal, unison is established as previously described; if visual signals are received, a series of corrections occurs in one direction or the other until the synchronizing signals are encountered and assume control, whereupon the procedure is as before. The cut-oi! relay thus functions to eflect a selection for control purposes between the synchronizing signals and the visual signals.

While it has been chosen to illustrate an arrangement by which synchronism is established from any out-of-phase position by means of a series of phase corrections, it is to be understood that the invention is likewise applicable to an arrangement in which the controlled element is released fromia predetermined phase position to establish initial proximate synchronism. An arrangement of the latter type is shown in my copending application Ser. No. 736,383.

Referring now to Fig. 8, the embodiment shown therein is characterized by the type of drive motor used, and the method employed to establish and maintain synchronism. Drive motor It is of asynchronous type, such as a shunt, series, or induction type, with or without governing means, in which the motor speed is controlled in some degree by the electrical resistance of the main or auxiliary circuits. It is assumed that the motors at the sending and receiving stations are regulated by any of the commonly used means to run in isochronism as closely as possible. Hesistors r and r' are in series with motor 80, and are shunted as required by break contacts X and make contacts X, respectively. Contacts X, X are actuated by corrector magnets MI and M2, as described in connection with Figs. and 7. It may be assumed, for example, that opening contacts X increases the resistance of the main motor circuit thus retarding the motor speed by a predetermined increment while closing contacts X decreases the circuit resistance, increasing the motor speed by a predetermined increment. Resistors r and r are preferably variable in order to facilitate the adjustment of the degree of the incremental speed changes. Without further analysis, it will be evident that the arrangements shown in Figs. 5, 7 and 8 are. in combination, adapted to accomplish automatic synchronization of a rotary controlled element with received periodic signals. It is to be noted, however, that the controlled element is moved to establish and maintain synchronism by incremental speed changes of the driving motor.

Referring now to Fig. 9, the embodiment shown is characterized by asynchronous drive motor 00, preferably of the type known as a phonic wheel or Lacour driving motor, supplied with power from a frequency regulated source. The main elements of motor 80 are the stator 80S and toothed rotor "R. The controlled rotary element, as for example disc 20 of Fig. 5, is mounted directly on shaft SI of motor 90, or on an auxiliary shaft geared thereto. Stator its is fed periodic unidirectional impulses by an impulse generator and amplifier as shown. The main elements of the impulse generator are discharge tube 94, illustrated as a two element "neon" lamp, battery 95, storing capacitor C3, timing resistor RI in shunt with C3, and transformer Tr. Photo-cell 23b and series resistor RI are in shunt with storing capacitor C3. Transformer Tr couples the impulse generator tothe impulse amplifier comprising electronic relay 8!, cut-off relay l3, and battery 96 supplying power to the anode-cathode circuit of relay 9!, which circuit includes the winding of stator 908.

The operation of the arrangement of Fig. 9 is as follows:To start the impulse generator, switch SW is closed, applying potential to discharge tube 94 which is immediately ionized thereby and becomes conducting. The flow of current thru tube 94 quickly charges capacitor C3 until the potential across tube 84 is less than its cut-off voltage, whereupon tube 94 deionizes and becomes non-conducting. The current imand when dark do not participate in determining P represents the normal pulse.

the frequency of the impulses, which is largely controlled by the characteristics of tube 94, and

by the values of C3 and Bi. When illuminated, photo-cells 23a and 23b modify the frequency of the impulse generator in a manner presently to be described.

Once the impulse generator is started, rotor 90R is brought up to synchronous speed by spinning by hand, or by an auxiliary winding or small motor, and is then maintained at synchronous speed by the impulse amplifier, in well known manner. Assume now thatwhen rotor 90R locks in step with the pulses, the controlled element, as for example disc 20 of Fig. 5, is ahead of its proper phase position. According to the conventions previously established, this would mean that retarding are 2012 would be presented to the flash of lamp 2| and thus photo-cell 230. would be illuminated. Photo-cell 23a (see Fig. 9) is connected in parallel with discharge tube 94, and when illuminated, its resistance is greatly reduced. Thus when photo-cell 23a is illuminated, a path shunting tube 94 is presented by which current flows into storing capacitor 03 at the same time that the charge of C3 is leaking oif impulse generator are slowed down, likewise slowing down rotor 90R and the controlled element mounted on shaft 9|. This action of extending the interval between pulses is illustrated in Fig. 10 in which P4 represents a delayed pulse, while P represents a normal pulse.

Next assuming that the controlled element is behind its proper phase position. then advancing are 201) will cause photo-cell 23b to be illuminated. Photo-cell 23b is connected in parallel with resistor RI across storing capacitor C3, and its effect when illuminated is to accelerate the discharge of C3, hence to hasten the following impulse. This action of shortening the interval between impulses is illustrated in Fig. 10 in which P2 which represents the accelerated pulse, while The function of variable resistors R2 and R3 is to permit of easy adjustment of the effect of photo-cells 23a and 23b on the timing of the impulses.

Without further analysis, it will be evident that by controlling the occurrence of the pulses applied to rotor 90R, the movement of the controlled element is likewise controlled. The controlled element is established in synchronism from any out-of-phase position by controlling the frequency of the power input to the drive motor, and is thereafter maintained in unison by means of frequency corrections similarly applied.

The novel form of impulse generator shown in Fig. 9 has the advantage of being comparatively simple and inexpensive, of being adjustable over a wide range, and of providing impulses of highly constant frequency. In the latter respect, by suitable precautionary measures well known to those skilled in the art, the constancy of this generator can be made to compare favorably with that of a high grade, electric tuning-fork oscillater. In the novel apparatus shown the use of photo-cells 23a and 23b permits of easy and instantaneous change in the pulse frequency-a result difficult to obtain with tuning-fork impulse generators. Thus, for example, the frequency corrections can be applied to single impulses this is practically impossible with tuning-fork impulse generators.

It will be apparent that the invention provides a system of synchronization which is relatively simple and inexpensive in construction, easy to operate and to keep in order, which is eflicient and reliable in action, and which meets in a highly satisfactory manner the manifold and exacting requirements for a system of this type.

While the methods herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In a synchronizing system, phase evaluating means including in combination, a light source modulated by received periodic signals, periodically moving light deflecting means provided with light deflecting surfaces having different inclinations, light directive means adapted to direct light from said source to a predetermined point in the path of motion of said deflecting means, and light responsive means actuated in accordance with any phase relation of said deflecting means to said periodic signals.

2. In a synchronizing system, control means adapted to effect the synchronization ofv a controlled element with received periodic synchronizing signals comprising, in combination, a signal modulated light source, a rotary element carrying a series of light deflecting surfaces having different inclinations, light directive means focusing light from said light source upon the path of motion of said series of deflecting surfaces, and light responsive control means actuated in accordance with the relation of the controlled element to a condition of unison with aforesaid nals, a rotary element provided with a plurality of 'light deflecting means comprising light defleeting surfaces having different inclinations, light directive means focusing light from said light source upon the path of motion of said deflecting means, and light responsive control means selectively actuated in accordance with the motion of said rotary element with respect to a predetermined condition of unison with aforesaid periodic synchronizing signals.

4. In a synchronizing system, in combination, synchronizing control means comprising a light source adapted to be modulated by periodic synchronizing signals, light directive means adapted to direct a light beam from aforesaid light source to a predetermined point, a rotary element provided with a plurality of peripheral light deflecting surfaces having different inclinations traversing aforesaid predetermined point, and a plurality of light responsive means selectively actuated as determined by said light deflecting suriaces.

5. In a system, synchronizing control means including actuating light means modulated by periodic synchronizing signals, a rotary element provided withmeans for deternlningatanypointinitsrotationitsownstatus with respect to a predetermined condition oi unison with the aforesaid synchronizing signals, said last mentioned means comprising light defleeting means having light deiiecting surfaces of diflerent inclinations, and light responsive control means selectively actuated by said light means as determined by said rotary element.

6. In a system, synchronizing means Including actuating light means modulated by periodic synchronizing signals, rotary means provided with means for determiningv qualitatively at any point in its rotation its own status with rmpect to unison with the aforesaid synchronizing signals... said determining means comprising light deflecting means having light deflecting surfaces of diiierent inclinations, light responsive means selectively actuated by said light means as determined by said rotary element. and motional control means for said rotary element actuated by said light responsive control means.

7. In a system, synchronizing means adapted to automatically synchronize a cimtrolled rotary element from any out-ot-phase position by said element, including light means modulated by periodic synchronizing signals, rotary means provided with light deflecting means comprising light deflecting surfaces having difierent inclinations for determining qualitatively at any point in its rotation its status relative to the aforesaid synchronizing signals, light responsive means selectively actuated by said light means as determined by said rotary means, and control means adapted to establish and maintain unison of said rotary element with said signals including means to utilize said synchronizing signals at any phase position of said element.

8. Ina-synchronizing system, means adapted to synchronise a rotary element with received synchronizing signals including drive means,-- a rotary element driven thereby, continuous phase indicating means carried by said rotary element and comprising light deflecting means having light deflecting surfaces of diflerent inclinations capable 0! indicating the phase status of said element at any rotational position, phase correctto bring a rotary element from any out-of-phase relation into unison with received periodic synchronizing signals including isochronous driving means, a rotary element driven thereby, continuous phase indicating means carried by said rotary element and comprising light deflecting means having light deflecting surfaces of different inclinations capable of indicating the phase status of said element at any rotational position, incremental speed correcting means for said driving means, means for translating synchronizing signals into flashes of light, a plurality of light actuated control means for said speed correcting means, said control means being selectively actuated by the cooperation of said phase indicating means and said flashes 01' light.

10. In a synchronizing system, means adapted to move a rotary element from any out-oI-phase relation into unison with received periodic synchronizing signals including synchronous driving means, frequency control means therefor, a. rotary element driven by said driving means, continuous phase indicating means carried by said rotary element and comprising light deflecting means having light deflecting surfaces oi different inclinations capable of indicating the phase status of said element at any rotational position, means for translating synchronizing signals into light flashes, and light actuated corrective means for the aforesaid frequency control means selectively actuated by cooperation of said light flashes and said phase indicating means.

HARRY J. NICHOLS.

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