US2406352A - Telephone privacy - Google Patents

Description

Aug. 27, 1946 w. A. MUNSON TELEPHONE'PRIXIIACY Filed Feb. 11, 1942 2 Sheets-Sheet 2 FIG. 4

lNl ENTOR WAMUNSON A TTORNEY Patented Aug. 27, 1946 UNITED STTES r'rsnr FFICE TELEPHONE PRIVACY Application. February 11, 1942, Serial No. 430,370

9 Claims.

The present invention relates to the use of rotary distributors for subdividing message waves on a time basis for transmission or reception. More particularly the invention relates to the problem of coordinating the movements of a recording medium such as a magnetic tape and a rotary distributor located at one point to the movements of similar apparatus at a distant point.

The invention will be disclosed, for illustration, as embodied in a speech privacy system in which speech is recorded on a moving magnetic tape and is subdivided on a time basis by a rotary distributor so arranged as to send out the fragments of speech in abnormal sequence to make reception by unauthorized persons difficult. A similar magnetic tape recorder and rotary distributor at the receiving point subdivide the received privacy speech and rearrange its parts into understandable speech.

It has been proposed heretofore to use various types of start-stop distributors for securing synchronism between the switching operations performed at separated stations in reproducing the recorded speech fragments and transmitting them in altered sequence. Where the brushes are stopped in their motion relative to the distributor segments once in each revolution, they must be quickly accelerated again when started and this sudden transition in both stopping and starting not only places a strain on the mechanism but can give rise to errors due to the variable accelerate time under different conditions. This has been true in prior art systems where all machines, both those running in exact synchronism and those having an error, are subjected to this stopping and starting in each revolution.

The present invention involves a species of start-stop operation but the brushes themselves are never actually stopped so long as they are running in exact synchronism. In a system involving a number of machines, only those operating with a speed error are subjected to the stopstart action of the brushes so that the machines running normally are not penalized by the fact that other machines may need correcting.

It is common practice in printing telegraphy to use start-stop distributors and to run th receiving distributor normally slightly faster than the transmitting distributor so that normally it is stopped for a longer time, in each revolution, than the transmitting distributor. Errors in speed of the receiving distributor result in Varying the duration of stoppage of the receiving distributor, and by running the receiving distributor starting pulses.

normally too fast a greater margin is allowed in stoppage time to compensate for speed variations. If the receiving distributor varies in speed by becoming still faster the stoppage period is:prolonged. If the variation is a slowing down, the stoppage time is reduced. It is customary in such systems to make the receiving distributor segments shorter than the transmitter segments so as to pick out the middle part of the transmitted pulse.

In a speech privacy system in which rotary distributors are used to subdivide the message waves as referred to above, the synchronizing presents a much more difficult problem since it is necessary to preserve as far as possible the entire'wave, which means that ideally each transition of the two distributors from one segment to the next should be made at the same instant and with minimum transition time. Moreover, if the same apparatus is to be used alternatively to transmit and receive for purposes of two-way conversation, the distributors must be capable of serving for either transmitting or receiving and cannot beof different design. 1w

It is possible to secure some of the advantage of running the receiving distributor slightly fast, by actually running it at the same constantspeed as the transmitting distributor but delaying slightly the sending out of the start impulse so that both distributors are normally stopped for an interval to allow a time margin in which to correct for errors in speed of the receiving distributor. This enables all distributors to be alike in construction, and when any distributor is converted from receiving to transmitting it is arranged, automatically to send out thedelayed All receiving distributors are then synchronized to the distributor that is at' the time transmitting. r r

The invention possesses certain of the. advantages obtained by use of the delayed startin pulse but avoids the attendant loss of a small percentage of the speech which has been experienced with certain types of apparatus using the delayed impulse method and avoids the stopping of the brush itself except when itis out of normal phase position.

In accordance with the embodiment of the invention to be specifically disclosed herein,=-the stop for the brushes is itself carried on a rotating arm so arranged that if the brushes are running at normal speed the stop is removed as'the brush carrier comes up against it, and no stoppage of the brushes occurs. If the brushes are-running in advance of normal they are stopped'momen- Figs. 4 and 5 are respectively views in plan" and elevation, partly in section, of rotary-distributor mechanism constructed in accordance with the invention; and V v Fig. 6 shows a detail of the movable stopin relation to the brush carrier.

The over-all system as"diagrammed-inFigpl will first be described. This system as shown is assumed to be the same as that disclosed in application for United States Letters Patent Serial #No. 401;908 :Iof i. G, :Buhrendorf filedlJuly ll, 1- 1941,:an'd only a cbrief description of-ittwill be cgivenfifhere sufficient to show how the. improved -idistributor mechanism of the invention maybe inserted into the system.

IniFigil a motor I (Lthrough a shaft? 9 l,;drives hrush- 13: ofca rotary distributor and also .drives easwheel:(ndthhown) having a magnetic tape "mounted on its rimzso asto move past the polepieces of a recording magnet l9 and a number .iWhen; stationliis usecLfor transmitting, mi-

v'cnoph-one'. I 'kisFspoken into and the1contacts in 'i the boxf 23, labelled talkreceive oircuittare put in'italkingposition so'that the speech waves: are '.';sent: to recordingfmagnet I I 9. this'recorded'speech moves along past therepro- The tape bearing :ducer'rmagnets: in succession and is reproduced inxeachiof 'themnin successive: phase. The'code :".switches in box- 24, and the talk receiveswitches f'ithereinpareiset:soas to connect certain specified OIlGS'IJOf these reproducerzmagnets 'to ,the five pairs of segments of distributor'ring .29 in acricordanceewith the particular code being used. theibrusharmii (after being released) sweeps iovertthesetsegmentsi the brush :bridges :the; seg- ;:ments:- in.- succession to the ring Lt!) so that .the sspeechffra'gments are sent over leads and :throughcontactsr in box 23: tooutgoing. line or achannel 22 leading to: station 2.

"a'Ihe shaft II also drives through gearsle'and 1-5; with slight speed reduction, arotaryicontact :maker in; the startimpulse circuit '25 which sends ea start impulseitozrelease magnet tie-once each -revblution and also to outgoingline'22 through :leadsZlcandcontacts in box 23.to start the :dis- .itributorrbrushes-of 'both stations .at theisame instant.

Inthel Buhrendorf disclosurethe brush .arm -I 3':is frictioncdrivenbyshaft H that it may be stopped -while the shaft continues to rotate.

':The tNo.'i5 segment .on which the brush is shown restingyina-Fig.lisshorter than the other. seg

mentsrandthe; relation is suchv that the normal .stOppa etime on'this short segment plusthe travel time across this segment both before and after the stoppage is just equal to thenormal .;time; of traveltof E. the brush across each: of the :Qther segments.- xThis is coordinated with z the flQiBIQrYQiH t'hB sending of the start impulse (due 'to ntheg earrreduction'ratio,of gear train it, l5) so.

--.that 'i'whenr-a ll machines are running: normally .-thes;. d;uratio nof the stoppage interval ;of :the

;-brushesz is. the same in all-machines. If a-receiv- 30' =iof reproducing'magnets'ia.as more'fully shown --:-in"theiBuhrendorf disclosure.

4 ing machine is slightly slow, the stoppage interval is shortened; if slightly fast, the stoppage interval is prolonged, in each case by the amount necessary to insure starting of all brushes at the same time. Whatever error exists within the capability of the mechanism to'correct it, is in this way wiped out at the conclusion of each rotation of the brush and is prevented from accumulating. The receiving machine or machines are governed from the sending machine by the sending out of the start impulse.

When the apparatus in Fig. 1 is used to receive from distant station 2, contacts are thrown in boxes 23, 2 3,. and v26 at each station so that stationl ends out the start impulse and the speech fragments in accordance with the code previously agreed upon. The speech fragments received over line 22 pass through contacts in box 23 to recording magnet i9 and the start impulses are sent through contacts in box 26 to the winding of release magnet 33; The reproducer ,magnets'22 pick 01f the recorded speech segments from the moving tape and these are sent through 7 contacts of the code switches to the five pairs of distributorsegments 29 in such manner that they are'swept off by the brush in normal speech order and sent to receiver is over leads-25 and contacts in box 23 in receiving position; The brush arm I3 is stopped at the end of each rotation by latch 32 and is released in time corre- -spondence with the distant transmittingdistributor under control of the start impulses.

In the construction accordingto the present invention all of the commutator segments have equal length and there'is no stoppage of the brushes on any commutator segment unless the brushes are running too fast andneedito'be stopped inorder to be brought into; proper starting phase. The'principle-of operation is -illustrated in the diagrams of Figs. 2 and 3. is a corrector arm' la driven slightly faster than the brush carrier A t-represented as a ring (actually it may be an arm) having a small'arc cut to present two limits as and'etto the relative movement of arm '43 with respect to :ring Hi. In Fig. 2 the normal relation is shown at the instant-of release of corrector-armes for the start of a rotation, the limit #25 just reaching the arm tl3 as the latter is released, so that the'movement of brush: ring as is uninterrupted. In Fig. Ethenurmal'relation is shown at the instant'of stopping of arm 43 at the end of a revolution. The normal stop interval is the'timerequired for the ring to move from it's Fig; 3 position to its Fig. 2 position.

If now the brush ring is too fast, the parts will reach the positionshown in Fig. 2 in advance of the, receipt of-the start pulse'from the "distant station and the brush ring will be stopped until the start impulse releases the arm 'If the brush ring: is running slightly behind/the parts Will-196111 the'position shown in Fig. 3 at the instant' of stoppage of the arm 43 because the arm 43 overtakes the limit at at some time'during the rotation and advances'the ring to the'Fig/3 position. The rin M, if' too slow, will not advance sufiiciently farduring the stoppage period of the arm 43 to reach the Fig. ,2 position by the time .arm 43 is released, but arm 453 willovertalze the ring at sometime during the revolution and for the remainder of the revolution the ring will travel withthearm and at the speed of the arm. 'Ihesrnall error with which the brushes'start out on a revolution will in this manner not be cumulative, but will again be the same '-at thecom- There pletion of the revolution. It will be observed that this is the opposite of the usual start-stop operation in which the brushes are started at the correct time, but, if slow, lag farther and farther behind during a rotation.

Referring to Figs. 4, 5 and 6, the motor I6 is mounted by suitable brackets on the bed plate 5i! which forms part of a housing for the distributor mechanism. the rest of the housing being indicated at 5!. Shaft H has keyed to it a pinion 52 which is formed integral with or has secured to it a sleeve 58 extending downwardly in Fig. 5 and terminating at its lower end in a flange 59. Mounted for rotation on this sleeve 56 is a larger sleeve 51 keyed to a pinion. 55 for rotation therewith. Idler gears 53, E i communicate motion .from gear 52 to gear 55 with a slight speed increase (e. g. 2 per cent). Arm 43 is enlarged into a disc surrounding the sleeve 56 to provide relatively larg surfaces for mounting between discs 58 of cork or other suitable friction material. The opposite end of the arm 43 extends toward the right in these figures and cooperates with latch 32 and release magnet 33 in the manner already described.

The brush carrier 44, indicated in diagram in Figs. 2 and 3 as a ring for convenience of description, is in the actual construction shown an arm similar in general to arm 43 in that it is enlarged into a disc at one end for mounting between friction discs 6i which are in turn held between flange 59 and washer 60. Arm 44 has brushes 5?. supported on its under side.

Arm 43 has a depending member 41 (see Fig. 6) bifurcated at its lower end to provide two prongs 45 and 46 between which the end of the brush carrier 44 extends. These are the limits 45 and 46 referred to in the description of Figs. 2 and 3. Assuming movement toward the right in Fig. 6, arm 44 will under normal conditions just be coming into contact with prong 45 at the instant of reaching the stop 32 and will just be coming into contact with prong 45 at, the instant of release of arm 43. If the brushes are behind, prong 46 will advance the arm 44 and if the brushes are ahead, prong 45 will stop the arm 44, as has been described above in connection with the diagrammatic Figs. 2 and 3. The friction discs 58 provide sufliciently greater friction than discs 6| so that arm 43 controls the motion of arm 44 in the manner described.

The invention is not to be construed as limited to the precise details or magnitudes that have been given herein but the scope of the invention is defined in the claims. which follow.

What is claimed is:

1. In a rotary distributor, a brush arm rotatable with respect to distributor segments, a stop therefor, timing means defining the starting time for each rotation of said brush arm, means to interpose said stop in the path of said brush arm a given interval in advance of the normal starting time representing a small fraction of a rotational period, and means controlled by said timing means to remove said stop at the end of said small interval whereby said brush arm is stopped only if it is in abnormally advanced phase at the instant of interposing said stop.

2. In a rotary distributor, a brush arm rotatable with respect to distributor segments, a stop arm also rotatable, engageable means between said arms for permitting said stop arm when stopped to stop said brush arm, timing means for defining the starting time for said stop arm in ill each rotation, means for rotating said stop arm in advanced phase with respect to said brush arm, means governed by said timing means to stop said stop arm in each rotation to permit said brush arm to approach said stop arm when the latter is stationary, said engageable means stopping said brush arm only when the latter is in abnormally advanced phase with respect to said stop arm at the instant of stoppage of the latter.

3. In a rotary distributor, a brush arm rotatable over distributor segments, a stop arm rotatable ahead of said brush arm and at a slightly greater rate, stop means for said stop arm, timing means to remove said stop means to permit said stop arm to begin a new rotation, and engageable means between said stop arm and brush arm for stopping the latter only when said brush arm overtakes said stop arm before the latter is released.

4. In a rotary distributor, a brush arm rotatable over distributor segments, a corrector arm rotatable with said brush arm and linked thereto by means permitting a limited small relative movement between said arms, means for driving said corrector arm at a slightly faster rate than said brush arm, stop means for said corrector arm and timing means for removing said stop means periodically to permit rotation of said arms.

5. A combination according to claim 4 including means for driving said corrector arm at such a rate in excess of the rate of motion of said brush arm that the corrector arm gains a distance equal to the extent of said limited relative movement during the normal time between the removal of said stop means and the next stoppage of said corrector arm.

6. In a rotary distributor, a brush arm rotatable with respect to distributor segments, and means for keeping said brush arm within certain limits of error in phase comprising a corrector arm rotatable with said brush arm and link means engaging said arms with a certain amount of leeway such that said corrector arm advances the brush arm when the latter is behind normal position and retards said brush arm when the latter is ahead of normal position.

'7. In a distributor mechanism, a segmented ring, a brush carrier rotatable relative thereto, a pair of stops on said brush carrier spaced apart by a small angular distance. a rotatable arm mounted to rotate with said brush carrier and to have its movement with respect to said brush carrier limited by said two stops, means to drive said arm slightly faster than said brush carrier, and means to stop said arm in each rotation for an interval equal to the normal time of travel of said brush carrier through said angular distance.

8. In a start-stop distributor, a brush arm, a segmented ring. means to rotate the brush arm relative to said ring, a stop for said brush arm, constructed to stop the rotation of said arm in each revolution in which said brush arm is in advance of normal position, and means to remove said stop to permit said brush arm to continue its rotation without interruption in each revolution in which the brush arm arrives at said stop in normal phase.

9. In a speech privacy system in which the speech waves are first recorded and then are reproduced for transmission in abnormal order, distributor means for breaking the reproduced speech into fragments fo rearrangement into and a brush arm rotatable thereover, a rotatable stop arm separate from the brush arm but mechanically linked thereto with provision for for said stop arm, whereby said. stop arm may be stopped in advanced phase with respect to 7 said brush arm, and timing means for releasing said stop arm before the brusharm reaches the limitrof said relative motion in each revolution in which the brush'arm is not ahead of normal limited relative motion between said arms, a stop 5 phase positio WILDEN A. MUNSON.

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