US2182000A - Synchronizing system - Google Patents

Description

Dc. 5, 1939. H. J. NICHOLS 2,132,000

SYNCHRONIZ :NG SYSTEM Original Filed Dec. '7, .1934 2 Sheets-Sheet 1 INV'ENTOR BY i 0 ATTORNEYS Dec. 5, 1939. H. J. NICHOLS 2,182,000

SYNCHRONIZING SYSTEM Original Filed Deb. 7, 1934 2 Sheets-Sheet 2 algiiNTOli v ATTORNEYS Patented Dec. 5, 1939 PATENT OFFICE SYNCHRONIZIN G SYSTEM Harry J. Nichols, Binghamton, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Original application December 7, 1934, Serial No.

756,486. Divided and this application September 24, 1938, Serial No. 231,464

4 Claims.

This invention relates to-synchronizing systems and more particularly to the synchronization of periodic elements in visual communication systems and constitutes a divisional application of the copending application Serial No. 756,486, filed December 7, 1934, issued March 14, 1939, as Patent No. 2,050,239.

' 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 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 enablesynchronization of the controlled element of a visual communication system to be accomplished automatically and with a high degree of precision.

A further object of the invention is to provide a synchronizing system in which the controlled element at the sending end ofv 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 controlledelement A further object of the invention is to accomplish the automatic synchronization of any num- 1 her of receiving instruments under the control of a single transmitting instrument, a' condition highly desirable in mass visual communication systems. I

A further object is to provide a systemof 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 isto accomplish automatic synchronization with relatively simple and inexpensive apparatus, which apparatus will be easy to operate and easy to keep in order, and will be eflicient 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 elements 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 commonly used arrangement will be used for illustrative purposes. There is usually a blank portion of each drum which is not effective in the transmission of impulses corresponding to the visual matter (briefly called the visual signals) 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 this period that the periodic synchronizing signals of the invention (briefly called synchronizing signals) are transmitted over the transmission system.

In accordance with the present invention, an 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 visual 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 par- ;ticularly to avoid introducing currents of excessive magnitude which 'might produce objectionable, effects 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 signals. -Hence a preferred arrangement is to distinguish the synchronizing signals by a distinctive frequency characteristic. In the interests of brevity, and for illustrative purposes, the synchronizing signals will be described as unidirectional, single impulses, but it is to be understood that the invention is not limited to signals of this particular form. I

At the receiving station, the synchronizing signals may be employed to release the controlled 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 synof periodically moving element.

chronism 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 altemative 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 51), show three phases of the operation of the control arrangement at a receiving station.

Figs. 6 and 6a show a phase corrector 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 figures, 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. 1, the rotary controlling element ID at the sending station is shown as a disc, but may be a drum, cylinder or any other form Light from a light source II is focused by a lens l2 on the edge of disc 50, as indicated. Disc 10 is provided at one point on its periphery with an inclined reflector or reflecting surface, such as notch Illa. 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 l0, light is passed from light source II to reflector Illa, and thence to photo-cell l3. A suitable mask (not shown) may be interposed between reflector 10a and photo-cell i3 to restrict the light beam passing therebetween to desired'size and propertions. Photo-cell l3 may bean 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 i 3 varies according to the illumination of its sensitivesurface. This varying current is amplified I by amplifier i6, and sent to the line as indicated,

or applied to modulate a carrier current in-well known manner. Since reflector Illa comes into action only during the underlap period, there is no interference 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. 1 is shown. Reflector Illa is, however, mounted on the end of a drum or cyllnder 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 l5. Hence when the light link between source II V and photo-cell I3 is completed by the intercession of reflector Ilia, light variations of comparatively high frequency are received on the sensitive surface of photo-cell 13.

The advantage of the flashing indicated by V, while the synchronizing signals are indicated at S and S. The single synchronizing impulse produced by the arrangement shown in Fig. 1 is indicated by S, while the series of alternating impulses produced by the arrangement of Fig. 2 is indicated by S. 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 fixed and sharply defined phase position, a synchronizing signal is generated and sentto the line in a. form adapted to the transmission system. This synchronizing signal is sent during the underlap period indicated by the interval 11., 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 20 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 20a. For purposes of illustration, it will be assumed that arc 20b, in cooperation with other control elements, will effect a slowing down, or phaseretardatlon, of the controlled element, hence it will be referred to as retarding arc 20b. Like 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|, of quickflashing type such as a neon lamp. The flash 5, lamp 2| will flash periodically in unison with l the synchronizing signal, but no effect is produced thereby on photo-cells 23a and 23b 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-jcells is negligible.

Referring now to Fig. 5a, it is assumed that null arc 20a'has just passed the unison point when the synchronizing flash occurs. Such condition, assuming prior unison, would indicate that disc 20 has speeded up slightly, and is running aheadof 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 are 200. 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 20 to be advanced thereby to restore unison.

Referring now to Fig. '7 which shows a preferred form of amplifier for use as ampliflers'24a, 24b of Fig. 5, each photo-cell 2311-, 2312 is associated 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 andhigh amplification factor. The cathode of photo-cell 23a is connected to the grid of relay 30, and photo-cell 23b is connected in similar manner to relay 3|. The anodesof bothphoto-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 associatedelectronic relays.

When photo-cells 23a, 2312 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 theanode current is negligible. When either photo-cell is illuminated, its resistance is greatly lowered, hence the potential of the grid to which it is connected is raised 7 positively. This rise in potential of the, grid of the electronic relay ionizes or trips; same.

causing a. large increase of anode current and energizing MI 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 through 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 4|! is provided with a reduction gear box 40a whereby the speed of drive shaft 4| is suitably reduced to drive rotary 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 48 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 similarpitch, is integral with sleeve 46a, the latter being rotatable on drive shaft 4|. Drum 42 is mounted on a flange Men the outer end of sleeve 46a. The edge of flange 20 is'chamfered in the same manner as that of disc 20 in Fig. 3, and functions in the same way. Bevel idler pinions 41, 41' are rotatably mounted 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, 5|.

Pawl 5|, when actuated by corrector magnet Ml,

of the ratchet wheels to ring gear 48. When ring I gear 48 is rotated though an angle of n degrees, bevel gear 46 will be rotated relatively to bevel gear 45 through an angle of Zn 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. Assumethat 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 are 201) will receive the flash of lamp 2| and will deflect same to photo-cell 23a. Referring for the moment to Fig. 7, upon illumination, photo-cell 23a trips electronic relay 3!] and a current discharge therethrough energizes corrector magnet Ml, the discharge being terminated after a predetermined interval by cut-off device 26. Upon being energized, Ml pulls in pawl 5| (see Fig. 6a) advancing ratchet wheel 50, and through the medium of worm 49, ring gear 48 and idler gears 41, 41'. The arrangements are such that idler gears 41, 41' move in the direction of rotation of the drive shaft, and drum 42 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 42 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 are 200 would have been presented to the flash of lamp 2|, and the corrector gear mechanism would have been actuated in the proper'manner to advance the phase of drum 42 to establish unison. Thereafter, 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 slightdeparture 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 1 procedure, it was assumed that the synchronizing signals alone were being received, or else that selective means of some kind, such as a filter. ef-

fected 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 though 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-off relay 26 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 '7 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 synchronizu,

ing signals are encountered and assume control, whereupon the procedure is as before. The cutoff relay thus functions to effect a selection for control purposes between the synchronizing signals and the visual signals. a

While it has been chosen to illustrate an arrangement bywhich 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 from a predetermined phase position to establish initial proximate synchronism. An arrangement of the latter type is shown in my copending application Serial 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 89 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. Resistors r and r are in series withmotor 80, and are shunted asrequired by break contacts)! and 'make contacts X, respectively. Contacts X, X are actuated by corrector magnets MI and M2, as described in connection with Figs. 5 and 7. It may be assumed, for example, that opening contacts X increases the resistance of the main motor-circuit'thusretarding 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 ar-' main elements of motor 90 are the stator 90S and toothed rotor 90R. The controlled rotary element,.as for example disc 20 of Fig. 5, is mounted directly on shaft 9| of motor 90, or on an auxiliary shaft geared thereto. Stator 908 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 R1 in shunt .with C3, and transformer Tr. Photo-cell 23b and series resistor R3 are in shunt with storing capacitor C3. Transformer Tr couples the impulse generator to the impulse amplifier comprising electronic relay 92, cut-off relay 93, and battery 96 supplying power to the anode-cathode.circuit of relay 92, which circuit includes the winding of stator 90S.

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 ionizes and becomes non-conducting. The current impulse through tube 94 energizes transformer Tr, which trips electronic relay 92, causing a current pulse to flow through the anodecathode circuit thereof, thus energizing stator 905. After a predetermined short interval, the current pulse is terminated by cut-off device 93. This action is repeated rapidly, and with great uniformity, since the circuit elementswhich control the frequency of the impulses may be made quite stable. Photo-cells 23a and 23b are shielded from light and when dark do not participate in determining the frequency of the impulses, which is largely controlled by the characteristics of tube 94, and by the values of C3 and RI. 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 that when 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 arc 20b would be presented to the flash of lamp 2| and thus photo-cell 23a 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 capacitorC3 at the same time that the charge of C3'is leaking off through resistor RI. Hence the impulses from the 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 arc 20b 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 represents the accelerated pulse, while P' represents the normal pulse. 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 R, 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 ap-' plied.

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 oscillator. 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 efficient 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 periodic impulse generators, in combination, a relaxation oscillator, means for regulating the normal rate of oscillation, and selective time regulating means therefor comprising two light responsive devices, one of said light responsive devices being adapted to increase the rate of oscillation, the other of said devices being adapted to decrease the rate of oscillation, and

synchronizing means for controlling the activation of the light responsive devices.

2. In periodic impulse generators, in combination, a relaxation oscillator comprising a steady source of potential, an electronic discharge device, electrical storing means in series with said discharge device, regulating means for controlling the normal rate of oscillation, and time control means for said relaxation oscillator comprising a light responsive device shunting said discharge device, and a second light responsive device shunting said storing means, and synchrom'zing means for controlling the activation of the light responsive devices.

3. In periodic impulse generators, in combination, a relaxation oscillator comprising 'a steady source of potential, electrical charge storing-means, an electronic discharge device cooperating therewith, regulating means for control: ling the normal cycle of operation of the cooperating elements of the oscillator; and selective light responsive means adapted upon being selectively energized to increase or decrease the normal rate of oscillation of aforesaid oscillator, and synchronizing means for controlling the activation of the light responsive means.

4. In a synchronizing system, the combination of a controlled rotary element, a synchronizing driving motor therefor, a periodic impulse generator for controlling the speed of the driving motor, said generator comprising a relaxation oscillator, and light actuated time control means for said relaxation oscillator, and synchronizing means for controlling the activation of the said light actuated means.

HARRY J. NICHOLS.

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