US2199546A - Synchronous communication system - Google Patents

Description

y 7,1940- H; J. mcHoLs 2,199,546

SYNCHRONOUS COMMUNIGAT I ON SYSTEM OriginalFiled May 22, 1933 s sheets-sheet 1 T Pn/zvrzR-si s fly. 1-14 BY 4&-

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SYNCHRONOUS CQMMUNICATION SYSTEM briginal Filed May 22. 1953 a Sheets-Sheet. 2

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y 7, 1940- H. 'J. NICHOLS 1 2.199546 SYNCHRONOUS COMMUNICATiQN SYSTEM OriginaIFiled ma 22, 1933 s Sheets-Sheet s [Wil I92 M i ia: 7

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smrmonous COMMUNICATION SYSTEM I Ori inal Fild May 22, 19s: a Sheets-Sheet, 4

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' SYNCHBONOUS COMMUNICATION SYSTEM Y driginal Filed May 22, 19s: a Sheets-Sheet e N w I E Q I Diaplacement y 1940- H. J. NICHOLS 2.199.546

SYNCHRONDUS COMMUNICATION SYSTEM Original Filed May 22, 1933 8 Sheets-Sheet 7 IN VEN-TOR. j W Muss s.

y 7, 1940- I H. J. NICHOLS 2.199.546

SYNCHRONOUS COMMUNI A'I'IQN SYSTEM ori inal-"Filed Ma 22, 19s: a Sheets-Sheet s Patented May 7, 1940 2,199,546 SYNCHRONOUS COMMUNICATION SYSTEM PATENT OFFICE Harry J. Nichols, Binghamton, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of NewYork Original application May 22, 1933, Serial No.

672,161, now Patent No. 2,104,570, dated January 4, 1938-.

Divided and this application -March 25, 1937, Serial No. 132,927

7 Claims.

This invention relates to synchronous communication systems and particularly to single impulse printing telegraph systems and is a division of the copending application Serial No. 672,161, filed May 22, 1933, patented Jan. 4, 1938, No. 2,104,570.

A general object of the invention 'is to provide a printing telegraph system in which single signal impulses, distinguished only in respect to time, are utilized to automatically establish synchronism, to provide continuous phase correction to maintain synchronism, and to select the printing characters and printing movements.

A more specific object is to provide a synchronizing and selective system, and suitable apparatus, whereby an electric typewriter, with minor modifications and changes, can be utilized as the printing mechanism of a printing telegraph.

A further object is to provide a printing telegraph system in which the greater part of the" apparatus is utilized for both sending and receiving functions with consequent advantages in economy. and in simplification.

A further object is to provide a printing telegraph system in which by the simple manipulationby the operator of a single switch, the apparatus is instantly placed inthe sending, receiving, or typing condition.

A further object is to provide printing telegraph apparatus utilizing a standard typewriter keyboard and with both lower case and upper case letters, figures, and characters, with automatic operation of carriage return, shift, spacer, tabulator, and back spacer, etc. so that telegraphic communications may be transmitted in the form of the usual commercial or personal letter. A further object is to provide printing telegraph apparatus of the speed, touch, and keyboard of a standard typewriter so that typists trained to operate the ordinary typewriter may, without special training, operate the printing telegraph apparatus described in the present invention.

A feature of the present invention is that the typewriter utilized as the printing mechanism of the printing telegraph system herein disclosed, when not being used for the transmission or reception of messages, is equally suitable for typing letters, reports, etc. of the usual nature.

A further object of the present invention is a simple calling signalling arrangement whereby initial calls can be made whether or not the driving motor is running, and while the typewriter is being-used for typing, and break-in calls can be made during transmission. the same appara: tus being utilized to eifect calling signals under the several conditions.

.A further object of the invention is to automanner and with exactness, synchronism between transmitting and receiving apparatus at separate points.

A further object is to accomplish such synchronism by means of single impulses transmitted at a definite phase position during each cycle of motion of the transmitting apparatus. A further object is to accomplish such syn chronisin by means of signal impulses suitable for transmission over telephone, telegraph, or .radio communication systems without special adaptation of such systems. A further object is to maintain close synchronism of the receiving apparatus by correcting, if necessary, and in. the degree necessary, the phase position of the controlled element once during each cycle of motion, ensuring that the controlled element moves at all times in close synchronism with the controlling element.

A further object is to provide a governor for driving motors for the synchronized elements which is accurate, sensitive, and quick in response, and which is compensated for tempera- A further object is-to provide a governor for the driving motor which permits. minor speed adjustments to be made electrically without ad-' justment of the mechanical settings 01' the governor and without impairing the range of operation and accuracy of regulation of the governor.

A further object is toprovide a motor speed control arrangement wherebymeans operable from a distance may be utilized to efl'ect a minor adjustment of the motor speed in -a predeter-' loss of control by the and which resumes the unoperated condition, 7

when a single periodic impulse is missed.

A further object'is to provide a phase vcorrecting mechanism which is simple in construction, accurate in operation, reliable and-durable, and

which automatically compensates for instrumental and line retardation of signals.

A further object is to provide a smooth -'acting phase corrector which while in continuousoper ation, will not tend to change the speed of the controlled element when running in synchronism.

A further object is to provide anelectromagnetic phase corrector which functions to correct the phase position of the controlled element without physical engagement therewith.

A further object is to provide non-repeat means in the sending condition whereby only one signal is sent to the line for each operation of a type bar key lever.

A further object is to provide interlock means whereby only one key lever may be depressed at a time.

A further-object is to provide a key latch and key release means whereby during sending operations, a key lever when depressed is retained in that position until the rotary distributor collects the corresponding signal, whereupon the key lever is released for return to the unoperated position.

A further object is to provide means ,whereby the key latch is held out of engagement with the key levers after release by collection of ,the signal, and thereafter as long as the key is held depressed manually, and is permitted to return to the position of engagement with all key levers when the held key is released.

A further object is to provide automatic cut-off be considered as parts of the same drawin show in diagrammatic form the circuits and apparatus which together with'the typewriter or printer comprise a complete communication unit. Fig. 1A shows the circuits and apparatus utilized in sending, receiving, and calling. The circuits are shown in the "typing condition, which is the condition when the selector apparatus is not being used for sending and receiving, and the typewriter is available for typing. Fig. 1B shows the power rectifier providing power for the various relays, magnets, etc. comprising the selecting ap- '50 paratus, and 'the distributor driving motor and its control.

Fig. 2 shows in diagrammatic form the circuits and apparatus utilized in sending, and for purposes of explanation is referred to as the sendin station or station "A".

Fig. 3 is a similar diagram of the circuits and apparatus utilized in receiving, and is referred to as the receiving station or station B- Fig. 4 is a similar diagram of the circuits and apparatus used in calling.

Fig. 5 is a plan view of the rotary distributor assembly including the plateau with segments and ring, the rotating distributor arm, and the cor- .rector magnet in relation to the distributor,

' preparatory for release to establish synchronlsm. Fig. 6 is a. side view, partly in section, showing the same assembly as in Fig. 5 and details of the hub, drive shaft, and friction drive. I

"Fig. -7 is a sectional view on line VIIVII of Fig. 6, looking towards the corrector magnet.

Fig. 8 is a side view showing a modification of the corrector arrangement, in which the corrector bar passes across the face of the corrector magnet 75 poles.

showing the distributor arm in the rest position Fig.- 9 is a plan view of the structure shown in Fig. 8.

Fig. 10 is a side view showing a further modification of the corrector arrangement.

Fig. 11-is aside perspective view of the corrector bar shown in Fig. 10.

' Fig. 12 is a pull-displacement diagram showing the general nature of the tangential magnet pull on the corrector bar by the corrector magnet.

Fig. 13 is a plan view of the electromagnetic clutch arrangement shown in the rest position.

Fig. 14 is a similar view, omitting the clutch magnet, and showing the clutch cam position for free rotation of the distributor hub.

Fig. 15 is a side view of the cam mechanism assembly shown in Fig. 14.

Fig. 16 is a cross section view of the clutch cam taken on line XVIXVI of Fig. 13.

Fig. 17 is a schematic circuit diagram, showing the part of the circuit associated with the clutch relay magnet.

Fig. 18 is an end view of the governor assembly.

Fig. 19 is a side view of the governor assembly.

Fig. 20 shows, in exaggerated form, the efiect of temperature on the thermal compensation means for the governor. I

Fig. 21 is a diagram showing schematically the arrangement for minor adjustment of the motor speed.

Fig. 22 is a fragmentary view of the key interlock, illustrating the principle of operation.

Fig. 23 is a side view, partly in section, of the solenoid assembly, the key interlock, and the key latch, showing the construction and arrangement of these parts. The spring link for connecting the plungers of the solenoids to the members which they actuate is also shown.

Fig. 24 shows the left end of the space bar assembly, showing the details of construction.

Like characters represent like parts.

General description,

A complete installation unit consists of an elec tric typewriter, a typewriter control assembly, and a distributor unit assembly. The typewriter control assembly is mounted underneath and inside the typewriter frame. The distributor unit assembly is housed in a case, and is located near the typewriter. The two assemblies are connected electrically by a multiple conductor cable.

The principal items of equipment comprising a typewriter control assembly are:

(a) The key solenoid assembly. (1)) The key switches.

(c) The auxiliary switch.

(d) The key latch. (e) The key latch release magnet.

(f) The key interlock.

In Fig. 1A, the apparatus comprising the typewriter control assembly is included within the rotary distributor.

dot-dash rectangle. All other apparatus is in? cluded in the distributor unit.

The apparatus shown in Fig. 1A performs the functions of transmitting and receiving printing impulses and synchronizing impulses, both of which classes of impulses are distributed via the Referring to Figs. 1, 5, 6, therotary distributor consists of a series of metallicsegments II, and solid metallic ring I2, both mounted on a disk It of insulating material, and the rotary brush arm I3, rotatably mounted on and ,yieldingly driven by the drive shaft 55. The ring and segments, while ac tually arranged in concentric circles, are shown in linear development in some figures in order to simplify the diagram. The rotary brush arm I3, which makes electrical connection from ring to segments, passes across all the segments once during each resolution in a well understood manner. The drive shaft 55 is conveniently driven at uniform speed by a motor 99, as hereinafter described. The brusharm I3 is shown in-the rest position on segment 3.

A clutch release relay I5 is provided to stop and to release the brush arm in accordance with the invention, and for illustrative purposes is shown with its armature I6 in engagement with the brush arm I3. The armature I6'also actuates springs I1 and I3 which function in connection with receiving operations.

The release relay I5 is provided with a low impedance winding 29 and a high impedance winding 2I connected in series. Across the terminals of the winding 2I' is connected a storing condenser 22. ,The outer terminal of the winding 29 is connected'to the positive bus 26; the

outer terminal of winding 2| is connected tospring I8, to spring I92 of the send-receive switch I96, and to one terminal of the corrector magnet 36. The release relay I6 is of .the quick acting, slow release type, and responds quickly to a short current impulse, but holds for a pro-- longed period, and if supplied with properly timed impulses continues to hold in the operated position as long as such impulses are regularly received. A relay which so operates is sometimes called a pulse sustained relay, and while other forms of such relays are in use, the particular form here disclosed is novel and constishown in Fig. 1B. The rectifier assembly con-: sists of the power transfer 2"], rectifier tube 2, preferably of full-wave type as shown, the filter condenser 2I2, and filter choke 2I3, all

connected as shown. The power transformer 2III has a primary 2, connected to the power mains I 2I1; secondary 2|! to supply heating current to the cathode'of tube 2I I; center tapped secondary 1 M6 to supply-anode 'current'to the tube 2| I; and secondary I 31 with center tap I36 to supply heat ing current to the cathode of the electronic relay The output of the rectifier is applied to theterminals of the voltage divided 24a and 24b shown in Fig. 1A. The positive bus 26 is connected to the positive terminal of the voltage divider, and the negative bus 26 to the negative terminal. 'The zero bus I3I is connected to the zero terminal between'sections 24a and 24b of the voltage divider,-the section 2411 thus furconnected to the zero bus I3I.

In series with the plate I35 of electronic relay I32 is the cut-off relay I10, connected as shown, with winding I'II shunted by variable resistor I12, and providedwith contacts I13 and I". As

is well known, the grid of. a grid controlled gaseous discharge tube is usually unable to stop the discharge when once started. and the plate. current is normally cut off by disconnecting the plate supply, or by causing the plate to become primary winding 26 and secondary winding 29;

and the receiving or input transformer 32 with center tapped primary 33 and secondary 34. The resistor 35, of a suitable value to balance the line impedance, is connected across the secondary 34, and across this resistor 35 appears the potential which overbalances the normal bias on the grid I33, and trips off the electronic relay in a well understood manner. The center tap of the primary 33 is connected to one terminal of the secondary 29, the other terminal being connected to the line terminal 30.

One terminal of the primary 33 is connected to the terminal 39 while the other terminal is connected to line terminal 3I through the artificial line network AL as shown. Y The functioning of duplex transmission being well understood, the operation is manifest and does not require discussion beyond that which will be given hereafter in connection with the calling circuits. f

The send-receive switch I99 is a three position switch, the three positions being indicated by RTS, referring respectively to the receiving, typing, and sending conditions. The switch is of the lever type and has one set of break-make springs, and one set of make springs. These springs are numbered from I9I to I inclusive. In the T and S positions, the send-receive switch mechanically holds the universal bar key latch IiiI out of engagement with the key levers I66."

The multiple switch relay I60, controlled by the send-receive switch I99, provides the a1 ito-' maticswitching operations required to change from sendinglcondition to receiving condition and, vice'f versa. It is provided with a single windingfI6I, and three sets of'break-make contacts numberedfrom I to 9 inclusive. In order to simplify the diagram, these contacts are shown in their natural locations in the circuit, and

are numbered I to 9 inclusive for the purpose The purpose of the reading condenser'arran ge- 1 pensates in part the inductance of the circuit of which it is a part.

Synchronization Referring to Fig. 2, the transmission of synchronizing impulses is accomplished as follows:

Assume that the brush arm I3 is frictionally driven, but is held in the rest position on segment 3 by the armature I6 of the relay I5. To start sending synchronizing signals, the sendreceive switch I90 is thrown to the S position, as indicated. This completes a circuit from zero bus through reading condenser I62 through winding I 6| of multiple switch relay via contacts Nil-I92 of send-receive switch to relay I5, through condenser 22 and winding 20 to positive bus. A strong current through this circuit operates multiple switch relay I60, breaking contacts 2-3, 56, 8--9 and making contacts I2, 4-5, 1-8. Release relay I5 is also energized, attracting armature I6 which releases brush arm I3. As condensers 22 and I62 become charged, a small steady current limited by resistor I63 flows through windings I6I and 2| providing sufficient holding current to hold the multiple switch relay and release relay in the operated condition. A strong operating pulse followed by low holding .current is thus provided, preventing over heating of the relay windings.

On being released by armature I6, the brush arm I3 is set in rotation by the friction drive, and takes up the uniform speed of the drive shaft set by the driving motor. When the brush arm reaches segment I, a circuit is completed from positive bus via contacts 81 through the pulse shaping network comprising the reading condenser. I65 and shunt resistor I66 and inductance I61 in series therewith,via contacts 4-5 to segment I, via brush arm I3 to ring I2, via contacts 2I through primary 28 to zero bus. For the duration of the contact of the brushes with segment I, current flows through the circuit just traced, a corresponding signal impulse is sent to the line by the, secondary 29 of the output transformer 21. This impulse, which is repeated for each revolution of the brush arm I3, is called the synchronizing signal.

It is to be noted that the synchronizing signal in its passage to the line from secondary 29 passes through primary 33 via the center tap, and thus through the equal sections of primary 33 to the line terminals. With the artificial line AL in proper balance the currents through the sections of primary 33 are equal, and in opposition, hence no voltage is induced in the secondary 34 and the grid I33 is unaffected by signals sent to the line under these conditions.

Referring to Fig. 3, the reception and application of the synchronizing signals at the receiving station is as follows:

At the receiving station, the synchronizing signals are received at the line terminals 30 and 3| and are applied to the terminals of primary 33 of the input transformer 32. The current from terminal 30 passing through the secondary 29 of the output transformer and the center tap branch of primary 33 is negligible.

The synchronizing signal through primary 33 induces a voltage across. secondary 34 and shunt resistor 35, which with proper polarity of the line terminals, opposes the bias voltage on grid m. The potential of grid m is thus made I5 will be more fully described hereinafter.

more positive and at a critical value depending on the characteristics of the relay I32 and the plate voltage thereon, relay I32 becomes ionized and conducting, and current fiows in the plate circuit. The brush arm I3 being at rest on segment 3, a circuit is completed from zero bus through center tap I36, and transformer winding I31 through cathode I34 to plate I35 via contacts I13-I14 through winding I1I via contacts I94I95 of the send-receive switch and contacts 3-2 to ring, via brush arm I3 to segment 3 via contacts I1I8 through condenser 22, through Winding 20 to positive bus. A strong current pulse flows through this circuit, operating release relay I5 and thereafter cut-off relay I10, which opens contacts I13-I14, terminating the pulse. The armature I6 is pulled in, releasing the brush arm I3, and opening contacts I1I8. The flow of current through condenser 22 has charged that condenser providing holding current for the-high impedance winding 2I, delaying the release of armature I6. The cut-off relay I10 releases quickly, being of low impedance, and being shunted by the resistor I12. Before relay I10 closes its contacts, however, the plate current has been interrupted long enough to permit the electronic relay I32 to de-ionize and the grid I33 to regain control. The electronic relay I32, with its associated cut-off relay, thus provides strong local current impulses which are initiated by the line signals, but which are of definite duration.

When released, the brush arm I3 is set in motion by its friction drive (and clutch as is explained hereinafter) and is thereafter rotated at uniform speed. Brush arm I3 having started from segment 3 shortly after the brush arm at the sending station passed segment I, would arrive at segment I before the arrival of the next synchronizing signal from the sending station, were it not for a slight delay in the operation of release relay I5 and the clutch mechanism.

Because of these delays which occur only during the first revolution, the lead provided by starting the brush arm from rest on segment 3 enables the brush arm to arrive at segment I as the next synchronizing signal is received. The synchronizing signal energizes the electronic relay I32 as before, but this time the circuit is completed via segment I as follows: via same circuit as before to ring, via brush arm to segment I, via contacts 5-6, through winding of corrector magnet 36, through condenser 22 and winding 20 to positive bus. The current pulse through this circuit replenishes the charge on condenser 22, maintaining the release relay I5 in the operated condition, and energizes the corrector magnet 36. The details of the operation of the corrector magnet 36 and release relay At this point it is to be observed that provided the brush arm I3 arrives on segment I when the synchronizing signal is being applied to the grid of the electronic relay, the charge on the condenser 22 is replenished, sustaining the operation of the release relay I5, and the corrector magnet 36 is energized. If these conditions are not fulfilled, release relay I5 drops out, and during the subsequent revolution the brush arm I3 is stopped on the rest segment. If the signals continue, the same procedure is repeated until synchronism is established.

In practice, it is found that with proper adjustment of the-clutch mechanism and by setting the rest position for the brush arm at the proper place, synchronism is usually established on the first revolution. Thereafter, synchronism if maintained by the corrector magnet correcting the phase angle of the receiving distributor arm to keep it in unison with the sending distributor arm. Should, for any reason, unison within approximately one half segment width be departed from, the brush arm I3 is stopped on the rest segment by reason of release relay I5 dropping out, and the synchronizing procedure is repeated when the next synchronizing pulse is received. Thus synchronism, if lost, is automatically re-established.

Sending circuits and operations Referring to Fig. 2, the printing signal impulse I transmitting apparatus includes the key switches I51 of break-make type, one for each key of the typewriter,- there being 49 keys on a standard typewriter keyboard. The armature spring of each key switch is connected to an individual Each key lever operates its associated key switch by means of an insulated push rod I50 as indicated. For transmitting purposes, each key lever when depressed is held down by the universal bar key latch I5I until released by'the key release magnet I52. The universal bail I53 is positioned below and transversely across the row of key levers, being held in light contact therewith by a retractile spring (not shown). When any key is depressed, 'the bail I53. closes the auxiliary switch I54 by means of push rod I55; One spring of the auxiliary switch is connected to the key switch bus I38; the other spring is connected to spring I42 of non-repeat relay I40.

' The non-repeat relay I40 has a low impedance winding I4B,.located on the heel .end of the core I40, and a high impedance winding I41. In series with the winding I41 is a reading condenser arrangement consisting of the condenser I48 and shunt resistance I48.

To commence sending, the send-receive switch is thrown to the S position, and synchronizing signals are sent to the line for a few seconds to permit the-receiving machine to cometo synchronism as described above. Printing signals may be sent by depressing the typewriter keys as for ordinary typing.

Assuming key 5 to be depressed, the operations which result are as follows: As the key lever nears the bottom of its stroke, the mechanism of the typewriter is tripped, and the typewriter immediately types the selected character to fur-.

nisha local copy of the message. The key lever is latched down in the depressed position by the universal bar keylatch I5I hooking over the end of the key lever I56. The finger can be at once removed'from the key. When the key is pressed down, the push rod I50 .(one for each' key switch connects the key switch bus ,I38 to thesegment associated with the particular key switch, in the present instance segment 5. When the brush arm I8 arrives at segment 5, a circuit is completed from positive bus, via contacts 81 through low impedance winding I46 of non-repeat relay I40, via contacts I44-I45 to key .switch bus I38, via middle and lower contacts of the operated key switch to segment 5, via brush arm I8 to ring, via contacts 2I through primary 28 of output transformer 21 to zero bus I3I. A strong current impulse flows through this circuit, its duration being determined by the time of contact of the brush arm I3 with segment 5, and a printing signal of the same duration is sent'to the line by the secondary 29 of the output transformer 21.

Non-repeat and key release arrangement The local current impulse just described, in addition to sending a printing signal to the line, also performs an important part in the non-repeat and key release actions. The local current pulse through winding I46 of non-repeat relay I40, together with the part of the pulse flowing through the high impedance winding I41, operates non-repeat relay I40, thus opening contacts I44--I45, and closing contacts I44-I43, and I42 -I4'I. Opening contacts I44-I45 cuts off the winding I46. Closing contacts 4-443 connects one terminal of the key release sole- .noid I52 to the key switch bus I38 and to winding I41. Closing contacts I42-I4I connects the zero bus I3I to the upper spring of the auxiliary switch and through its contacts placeszero potential on the key. switch bus I38. Any connected segment, except thesynchronizing segment, is therefore likewise placed at zero potential and no more printing signals can be sent to the line. This constitutes the non-repeat feature.

Closing contacts I42-I4I also completes a circuit from negative bus via contacts I4II42, via contacts of the auxiliary switch, through winding I41 and reading condenser I48 via contacts 8-1 to positive bus. Current through this circuit reenergizes non-repeat relay I40 and supplies holding current therefor. A second circuit is com- -'pleted from positive bus via contacts 8-1 through the winding of the key release solenoid I52, through reading condenser I18 via contacts -I43I44, via auxiliary switch contacts, via contacts I42-I4I to zero bus. A current pulse through this circuit energizes the key release solenoid I52, whose plunger pulls the key latch I5I away from the key levers by means of' the extension I82 as shown. r

If the'flnger is removed from the freed key, the key lever is drawn up by its retractile spring and the-springs of the auxiliary switch I54 lift the push rod I55 and open the contacts.

Opening these contacts breaks the circuit ,to

zero bus via contacts I42-I4I, and takes theholding current from the non-repeat relay I40 and key release solenoid I52, which thereupon release. Zero potential is also removed from the key switchbus I38 and any connected segment. When the key release solenoid I52 releases, the key latch I5I is returned to an engageable position by the retractile spring I83. When the n'oncontacts I4I-I43 and liberately held down, repeat signals are not perparatus nor as regards the accuracy of trans-' mission. In normal operation the keys are depressed and released quickly by the operator, and are released by the key-release solenoid practically instantaneously when the printing signal is sent to the line.

Key interlock It will be apparent fromthe foregoing description of sending operations, that a variable interval intervenes between the closing of a key switch and the collection of the impulse from the connected segment by the distributor brush. This interval depends on the speed at which the distributor rotates and the angular travel of the brush arm in order to reach the connected segment, the interval being always less than the time of one revolution.

It is manifest that if two keys were pressed simultaneously, or almost simultaneously, the distributor would send out a printing signal from the first connected segment, whether or not this was the proper order for transmission. To eliminate errors of this kind, a key interlock is provided which permits only one key at a time to be depressed. While various forms of interlock have been devised and employed, the preferred form is shown in Figs. 22 and 23. This form of interlock is well known, and its operation being familiar to those current with the art, detailed description is not required.

The principal parts of the interlock are the comb 235, the roller race 234, and the rollers 236, one for each key lever plus one. Each key lever is located in an individual slot in the comb 235 as shown. The diameter of the rollers is exactly equal to the key space centers, and the space between all the rollers combined is slightly greater than the thickness of a key lever I55. As indicated in Fig. 22, when one key lever is depressed, the slots for all the rest of the key levers are blocked.

Dual space segment arrangement With a single impulse system as herein described, the duration of the signal impulse is determined by the number of segments on the distributor and the speed of rotation of the distributor arm.

There is a practical lower limit to the duration of the signal impulse, since the shorter the impulse, the higher the required frequency characteristics of the transmission system connecting the sending and receiving stations. As is well known, all communication systems have definite limits as to frequency characteristics, the

limits being particularly restricted on telegraph cable circuits. One of the limitations on the speed of operation of printing telegraphsystems is therefore the length of the signal impulses and the number of segments on the distributor and the speed of rotation of the distributor arm are subject to this and other limitations.

One of the features of the present invention is the means by which the number of words transmitted'in a given time is increased without a An average word in telegraphic practice consists of five letters and a space, and the-speed of transmission is rated on the basis of the number of equivalent average words sent per minute. On the average, since a space occurs for every five letters, one sixth of the signals are space signals. In the present invention, means are provided whereby the average time required to collect and transmit a space signal is approximately one half that required to collect and transmit other printing signals. The means is to provide two segments for the space signal located" approximately diametrically opposite on the distributor. These segments are connected in parallel, and either one can transmit or receive a space signal. The arrangement is indicated by the connection of segments 8 and 36 in Fig. 1A. Thus, when the space bar is depressed, the distributor arm on the average moves only one quarter revolution until the signal is collected; for other signals an average movement of one half a revolution is "required. As an example of the advantage of this improvement, assume that the distributor arm makes 4 revolutions per second. The theoretical average speed of transmission, using only one space segment, would be:

Using the dual space segment arrangement, the theoretical average speed would be:

4X60 87 words per minute (approx.)

Sine wane impulse feature As is well understood, a sine wave impulse undergoes the minimum distortion in transmission, and permits the design of circuits of minimum impedance for a given frequency. Also, the problem of suppressing sparking at contacts is rendered less diffcult. One of the features of the present invention is means whereby virtual sine wave impulses are generated in the local circuits, and the signals sent to the line are of approximate sine wave form. In the sending circuit, the means for forming sine wave impulses comprise the storage condenser I86 across the voltage divider 24a and in series with section 24b, to-

gether with wave shaping arrangements and" proper design of the circuit constants of inductance, resistance, and capacity. In the sending circuit connected to segment I for generating synchronizing impulses, the wave shaping arrangement comprises the reading condenser I65 and shunt resistor I66, and inductance I61 in series therewith, together with the storage condenser |86 and the primary 28 of the output transformer 21, cooperate to produce a sine wave impulse in this circuit, and virtual sine wave synchronizing signals are sent to the line. In the printing signal circuits, the storage condenser I86, the reading condenser I48, windings M8 and 141 of non-repeat relay I40, and the primary 23 cooperate to produce sine wave impulses in these circuits.

Receiving circuits and operations Synchronism having been established as previously described, and the brush arms at the receiving and sending stations being in unison,

sister 35 opposing the negative bias on grid I33, which on becoming sufficiently positive triggers 011 the electronic relay I32 which becomes conducting. A circuit is thus completed from zero bus I 3| through center tap I35, and winding I31, from cathode I34 to anode I35, via contacts I'M-I14 through winding I1I, via contacts I34-I95, via contacts 3-2 to ring, via brush arm I3 to the particular segment with which the 10 brushes of distributor arm. I3 are in contact. From this segment, of which segment 5 may be considered as an example, the circuit continues via the middle and upper contacts of key switch I51 to winding I59 of key magnet I58 to key 15 magnet bus I39, thence via contacts 89 to positive bus 25. The pulse through this circuit energizes cut-01f relay I10 and key. magnet I58, whose plunger is attracted, stretching spring link I84 which pullsdown the key lever to'which it is 20 attached. The key lever trips the typewriter mechanism (not shown)- and the character is printed. As the key lever nears the end of its downward travel, the push rod I50 breaks the middle and upper key switch contacts. Owing 25 to the inductance of the key magnet, the inertia of the plunger and the key lever, and the action of the spring link I84, the breaking of the key switch contacts is retarded and the circuit is actually broken by the opening of the contacts 30 "3-414 by the cut-ofi relay I10. The length of the printing impulses and the synchronizing impulses is thus determined by the setting of the cut-off relay I10, and this relay is in practice adjusted to cut-ofishortly before the termina- 36 tion of the line signal. In this way, the circuit is normally broken at contacts I13-I14, which may be provided with a spark suppressor arrangement to suppress sparking at these contacts. With perfect unison, the circuit is broken before the 40 brushes leave the connected segment, hence sparking at the distributor is minimized, such.

sparking as occurs being principally due to the inductive energy in the key magnet. The sparking at the contacts of the key switches is neg- 45 ligibie.

It is to be observed that when receiving printing signals, the key magnet energized is that which is connected to the segment being contacted by brush arm I3. When the brush arms 59 at the sending and receiving stations are in unison, the key magnet selected at the receiving station will correspond with the key switchclosed at the receiving station. Accuracy in selection thus depends on close unison of the brush arms,

5 and cutting oil the printing impulse before the brush arm at the receiving station has carried over into contact with the adjacent segment. The corrector magnet provides the required close unison, and the cut-off relay terminates the im- 00 pulses, both synchronizing and printing, after a definite interval. The line retardation and ionizing time of the electronic relay are not material factors with the present invention, since the synchronizing signals are subject of the same delay as are the printing signals, and the corrector I magnet automatically compensates for this delay. Likewise, any instrumental delays fromline relays, etc. interposed in the transmission system are automatically compensated for.

10 While 'forillustrative purposes, the sending Calling circuits and operations Referring to Fig.-4,-which shows the calling circuits separated from the other circuits, the

apparatus receiving the calling signals from the line include the artificial line AL, and the pri- 10 mary 33 of the input transformer 32. The apparatus for utilizing the calling signals comprise the .secondary 34 of the input transformer, the glow lamp 202, the electronic relay I32, the cutout relay I10, the send-receive switch I9Il,.and 15 the call bell I. The send-receive switch I30 controls the calling circuit. When the send-receive switch is in either the ,typing or sending positions, the call bell is connected in the calling circuit; when the send-receive switch is in the 2 receiving position, the call bell is disconnected.

Assume the send-receive switch at the receiving station is in a typing position and that the machine is being used for typing purposes. To call, the sending station throws the send-receive switch to the S position and sends synchronizing signals to the line as described under synchroni zation. From terminals 3fl 3l of the receiving station, the signals traverse the circuit from terminal through primary 33 through artificial 30 line AL to terminal 3|. Some current flows through secondary 29, but the primary 28 is open, and this current is ineffective. The signal impulses through the primary 33 induce potential variations in the secondary 34 and these varia- 35 tions are applied to the grid I33 as previously described. The grid I33 ionizesthe electronic relay I32 which becomes conducting, and a circuit is completed from zero bus I3I through elecwinding I" of cut-oil relay I1Il,.via contacts I94I93 through winding of the call bell 2M. to

positive bus 25. Current flowing in this circuit energizes the call bell, and also cut-oii relay I10, which operates and breaks the circuit in the usual way. This action is repeated as each synchronizing impulse is received. Since the cut-off relay opens the circuit after each pulse, the interrupter in the bell can be dispensed with.

To stop the bell, the send-receive switch is '50 thrown to the receive position which opens the calling circuit, and establishes the receiving circuit as shown in Fig. 3. The receiving distributor is then synchronized, as previously described, and transmission begins. '55

The second calling situation is that existing when a station is sending and the receiving station wishes for some reason to call back. This is the so-called break-in" call, Referring to Figs. 2 and 3, the circuit conditions at the sending station are shown in Fig. 2, those at the receiving station in Fig. 3. To make the break-in signal, the receiving station throws the send-receive switch to the send position, changing its circuit conditions to those shown in Fig. 2, and syn- I15 chronizing signals are immediately sent to the line in the reverse direction, i. e., from receiving I station to sending station. The calling circuit at the sending station is in the condition shown in Fig.4, the send-receive switch being in the position shown by dotted lines. Due to the duplex arrangement ofthe transformers, previously described, the received synchronizing signals actuate the electronic relay I32, and the call bell is energized as previously described. Due to the I balancing effect of the artificial line, the outgoing signals do not actuate the electronic relay. Without further analysis, it will be evident that a called station can acknowledge the call, and signal ready, by throwing the send-receive switch momentarily to the send position in answering a call, and before moving to the receive position. The calling station is thus informed of the readiness of the called station, and can start sending without delay. 2

In the foregoing, the call signal device was described as a bell. It is obvious, however, that any of the usual audible or visual signalling devices, such as buzzer-s, gongs, annunciators, lamps, etc., can be employed, the power in the calling circuit being adequate for operating such devices and such variations are included within the scope of the invention as defined by the generic claims.

It will be observed that in the foregoing description of the calling system, two-way communication circuits were assumed. When oneway circuits, such as radio circuits, are employed, break-in and call-back signals are not usually feasible and the usual calling conventions for one-way circuits must be observed.

It is further to be observed that with the calling system described, it is not necessary that the distributor motor beturned on, but that power must be supplied to the electronic relay. To receive a'calling signal without having power on the electronic relay, a small neon .glow lamp 202 is connected into the calling circuit at some convenient point, as for example across the second-,.

ary 35 as indicated in Fig. 4.

It will be perceived that I have provided a simple and flexible calling system which is very economical in cost, and which possesses numerous advantages.

The electronic relay The electronic relay I32 may be of the hot cathode type, as shown, or of the cold-cathode type, in which case the cathode heating transformer I3! is not required. As is well known, the grid potentials suiflcing to ionize electronic relays is comparatively low, and they are therefore susceptible to stray potentials. inductive effects, etc. and for best results, measures to insure stability in operation are desirable. In the present invention, stabilizing measureswhich have been found effective comprise the grid current limiting resistor 203, the grid to cathode by-pass condenser 204, and the grid potential stabilizer arrangement consisting of the ballast condenser 205 and the ballast resistor 206.

The function of the current limiting resistor 203 is to limit the grid current to moderate amounts during the periods when the grid is positive. It is preferably of a comparatively high value, values of 50,000 to 500,000 ohms giving good results. The function of the grid to cathode by-pass condenser 204 is to by-pass high frequency and inductive potentials, preventing ionization of the relay from these effects. This condenser may be of comparatively small size, capacities of the order of .0025 mfd. having been found to give good results.

I86 is lost, and current flowing through bias resistor 24b to replenish the charge on condenser 86 causes a momentary variation in drop across 24b. The potential across ballast condenser 20S, and consequently'the grid bias potential, remain almost constant during such variations, since because of ballast resistor 206, any change in the charge on condenser 205 is retarded. The time constant of the combination of condenser 205 and resistor 206 is proportional to the product of The rotary distributor and phase corrector In Figs. 5 and 6, which show in detail the rotary distributor and corrector magnet assemblies, the rotary distributor is seen to consist of a hub 31, with diametrically positioned contactor arm 38 and corrector arm 39 mounted in cross holes 40 therein by suitable holding means such as set screws 4|. On the contactor arm 38 is mounted a link 42 of insulatingmaterial by means of screw 43, extending axially into the outer end of contactor arm 38. On the project- 'ing end of link 42 is mounted the brush arm l3 by means ,of a screw 44, extending axially .into arm l3. The outer end of the arm I3 is cut into half-cylindrical section, and on the cut section is mounted the half-cylindrical brushclamp 45. Between the flat surface of arm I! and clamp 45 are clamped two flexible metallic brushes 46 by means of a screw 41. The outer ends of the brushes 4B slope rearwardly and contact the segments II and ring l2 with a lightpressure. The brushes are conveniently made of copper braid, bundles of small copper wires,

' or silver strips, as is commonly practiced in the telegraphic art.

The corrector arm 39 carries at its outer end the corrector bar 49 of magnetic material, preferably a metal or alloy of low magnetic permeability such as soft pure iron, or magnetic nickel alloy. The corrector bar may have a variety of shapes, the preferred shape being shown in Figs. 6' and 7. The corrector bar should be rigidly mounted on the corrector arm, and is so mounted conveniently by positioning in a slot cut in the end of the corrector arm, and secured therein by one or more screws 48 (one being shown)- as clearly indicated. In the preferred form, the location and length of the corrector bar 49 is such that on rotation of the distributor hub, the corrector bar passes end-wise between the pole pieces 50 with a small air-gap at each end. The air-gap which has been found preferable is of the order of .025 inch. The corrector magnet 36 is preferably mounted on a bracket 52, adjustable in an are by means of curved slots 53 and screw 54, so that the poles 50 of the corrector magnet 36 may be adjustable sidewise concentrically with the drive shaft 55. By this adjustment, the corrector magnet 36 may be moved in relation to the synchronizing segment I. The need for this adjustment will be evident when it is considered that a small interval of time is required for the flux 7 in the corrector magnet 36 to build up in response to the synchronizing current impulses, this interval in part depending upon the induct-' ance in the corrector magnet circuit. During this small interval, the distributor arm moves in the direction of rotation, hence the'corrector magnet for proper action should be displaced angularly in the same direction by a slight amount arcane in excess of the mechanical angle of 180 represented by the axis of the corrector arm and the The best proportions for the faces of the polesof the corrector magnet, and forthe corrector bar may be in part determinedby analysis,..but refinement in the design of these parts is most readily obtained by experiment, The result desired is that the corrector bar should pass between the poles of the corrector magnet without material retardation or acceleration when the distributor arm is in perfect synchronism with that of the sending station, but shall be subject to corrective action when the synchronous relation is departed from.

Figs. 8 and 9 show a modification of the corrector bar-corrector magnet arrangement, in

which the corrector 49 passes in front of the poles 50 of the corrector magnet 36. The poles 58 are in this case narrowed at the face nearest the corrector bar to substantially the width of the corrector bar,- as shown. On analysis, it will be evident that as the corrector bar approaches or departs from the poles G, a tangential magnetic pull will-be exerted. The correcting action will therefore be the same as for the forms shown in Figs. 6 and '7. The strong radial pull, however, requires increased rigidity for the drive shaft to resist this unbalanced pull. This unbalanced radial pull, together with the fact that the correctorsbar 49 of the form shown in Figs. 8 and 9 is for the same magnetic efliciency heavier than that shown in Figs. 6 and 7 represent.

comparative disadvantages for the first .named type.

Another possible modification of the form of the corrector bar and corrector magnet poles is shown in Figs. 10 and 11. Since this modification represents a combination of those previously discussed, its action is manifest and further discussion' is unnecessary.-

Various other combinations of pole pieces and corrector bar shapes are possible, and such variations are included within the scope of the invention-as defined by the generic claims.

Fig. 12 shows atypical tangential magnetic pull-displacement curve. The ordinates represent, in arbitrary units, the tangential component of the magnetic attraction of the poles 50 on the corrector bar 45 shown in Figs. 6 and 7. The abscissae represent the displacement of the vertical median plane of the corrector bar from the median plane of thecorrector magnet poles. The arrows within the diagram indicate that %the pull is towards the median plane of the corrector magnet. From this curve it'is evident that a tangential force tends to hold the corrector bar in alignment with the corrector magnet poles.

Assuming-the corrector magnet to be energized 'by uniform direct current, this force depends on the amount ofthe displacement of the corrector bar from the median plane of the corrector poles, increasing rapidly to a peak value and then declining. For exact coincidence of the poles. some'distortion of curve doubtless occurs. Also, the synchronizing current impulse is of a general sine-wave form, causlngfarise and fall in the magnetizing force of the-magnet. Practical experience indicates, however, .that the curve shown in Fig. 12 represents substantially the corrector-bar is rapidly between the .the corrective action of the corrector magnet on the corrector bar to maintain the latter in unison with the sending distributor arm.

Referring to Fig. 6 which shows details of the drive shaft hub assembly, the hub 31, preferably made of a light metal such as aluminum, has a cylindrical axial bore 56 fitted to gtve a free turning fit onthe drive-shaft. A drive collar 51 lindrical cavityqinthe lower end of thehub 37.

and is adjustably secured therein by any preferred means, as .bythe set screw 66. Assembled on the hub collar 62 next. to the hub is the stop flange 65, being secured thereto by welding or other preferred means. The stop flange is extended radially at one point on its periphery to form an ear es as shown. .The purpose of this construc-' tion is to permit of ready angular adjustment of the ear 65 on the stop flange65 in relation to the distributor arm to enable proper setting of the rest position of the brushes 66 to be made.

To the top of the hub H is demountably assembled the friction cup Bl, held from rotating counter-bored to contain a friction pad 68 of soft material, preferably a firm felt ring. The upper end of the driveshaft 55 is reduced in section and is threaded. Thereon is screwed the adjustable friction nut 69, provided with a radial set screw it to retain the friction nut in the position of adjustment.

The friction pad se is liberally oiled and on being compressed, oil works down the shaft along the bore of the hub to the friction washer 6! to provide lubrication of these parts. The friction nut is adiusted until the distributor arm is driven with little if any slip. The arrangement shown permits of an easily adjustable, smooth acting friction drive for the, distributor arm which is found to stay in adjustment for extended periods.

v The clutch mechanism Referring to Figs. l3, 14, 15 which-show the assembly of mechanism by which synchronism is established-adjacent to the rolls 59 and 63 and .with axis parallel with the shaft 55 is rotatably mounted the double cam 12 located so as toengage circumferentially the rolls 59 and- 63. The cam 12 rotates on the spindle I3 mounted perpendicularly on plate it by riveting. Underneath the cam I2, slidably mounted on plate 14, is the cam detent 15. The cam detent l5 pivots. at one end on the pivot pin 18. In the middle section of the cam detent is a curved slot 11, through. which extends thestud screw 18. This screw prevents the cam detent from rising out of place and limits its travel. The free end of the cam detent is bifurcated, and the two prongs turned up toform pawls 80 and 8| which alternately engage-the lower stop 82 on the double cam 12. Extending through the cam detent 15, between the slot "and the pin 16, is located a small hole 83, through which is assembled the crank-shaped end of the operating ilnk 84. The other end of link 84 is threaded and to it is assembled the adjustable clevis 85. The clevis 85 is assembled to the armature l6of the release relay 5 by a pin 86.

The cam 12 is provided with a projecting upper stop 81, located on the top surface, and diametrically opposite the lower stop 82. This upper stop 81 is engageable by the ear 66 of the stop flange 65 in one position of the cam 12. The diameter of the cam 12 is reduced at the middle by the groove 98 (see Fig. 16). Extending into and across the groove 98 is the accelerating spring 9| which bears near its outer end against the accelerating pin 92, as shown. The accelerating spring 9| is looped in several turns around a pin 93 rigidly mounted in the plate 14. The fixed end 94 of the accelerating spring 9| bears against the pivot pin 16. The accelerating pin is so formed that when assembled as shown, the free end bears with moderate pressure against the accelerating pin 92.

The circumference of the double cam is serrated with a straight knurl except over an arc of approximately 90 in the region of the upper stop 81, where the radius is reduced and the cam edges are left smooth. This are of the cam clears the rolls 59 and 63 when adjacent thereto.

The operation of the clutch mechanism is as follows: When the parts of the mechanism are in the position shown in Fig. 13, the short pawl 88 engages the lower stop 82, stopping the double cam in such position that the upperstop 81' is virtually on the line of centers of the rolls 59 and 63 and the double cam 12. In this position the smooth edge of the cam is adjacent the rolls 59 and 63, providing clearance therebetween. The

. hub 31 can therefore continue rotation until the ear 56 engages the upper stop 81, which stops the motion of the hub and the brush arm is stopped in the rest position on segment 3 as shown in Fig. 5. Since the hub 31 is frictionally driven, the drive shaft 55 and the roll 59 continue in rotation.

Assuming now that the release relay I5 is ener gized, the armature l6 pulls the link Bd which in turn draws the cam detent 15 away from the cam. The short pawl is thus pulled out of engagement with the lower stop 82, releasing the cam 12. The detent 15 is drawn to the position shown in Fig. 14. The accelerating spring 9| by exerting force on the accelerating pin 92 causes the can: 12 to rotate quickly in a counterclockwise direction. This rotation of the cam 12 brings its serrated edges into engagement simultaneously with rolls 59 and 63. Since roll 59 is securedto the drive collar 51, and roll 63 to the hub collar 62, when the cam serrations grip the rubber rolls '59 and 63, the hub 31 is virtually locked to the drive shaft. It is to be noted that this is not a friction clutch, since the serrated cam edges mesh with the rolls 59 and 63 without slipping and as though geared thereto.

The cam 12 isrotated by reason of' being engaged by roll 59, and the upper stop 81 is rotated away from the car 66, removing these members from engagement. The cam 12 continues-to rotate until it reaches the position shown in Fig. 14, when the lower stop 82 comes into engagement with the long pawl 8|, stopping the cam. In this position the smooth arc is adjacent the rolls 59 cuit, comprising part of the and 63 and the hub 31 is freely driven by the friction drive previously described. The ear 66 link 84 pushes the detent 15 back into the position shown in Fig. 13, disengaging pawl 8| andlower stop 82. The accelerating spring 9|, which has been placed in tension on the accelerating pin 92 by the rotation of cam 12, now rotates cam 12 through a short arc, bringing cam 12 in the position shown in Fig. 13. When the ear 66 arrives at the upper stop 81, the hub is stopped and conditions are restored as at the beginning of the cycle described above. It is to be observedthat the mechanism just described provides'a definite, but adjustable, stop or rest position for the brush arm I 3; that on operation of the release relay l5 the driving shaft 55 and hub 31 are quickly clutched together in a positive manner to bring the hub 31 up to the speed of the driveshaft; that the-positive action of a gear clutch is obtained without the difficulty of possible clashing of gears if engaged in the wrong position; and that the clutch action is controlled with the application of but little force on the part of the clutch release magnet; The accelerating spring 9| minimizes the interval required for the clutch to act after the release relay is energized.

It is obviously possible to eliminate the clutch mechanism and cause. the link 84 to engage and stop the ear 66 without the intervention of additional mechanism. The frictional torque of the friction drive is, however, restricted to a small amount, otherwise the pull of the corrector magnet 36 will be insufficient to overcome the frictional torque. The proper frictional torque for good correcting action is incapable of accelerating the hub 31 and the distributor 'arms mounted thereon without considerable slip occurring. Furthermore, in practice it is found that such slip during acceleration is variable to such an extent that the corrector arm bar 49 does not reliably come into position between the poles 58 when the hub is accelerated solely by the normal frictional driving torque. The object of the clutch mechanism is therefore to establish synchronism in a single revolution in a certain and reliable manner.

The release-relay Referring to Figs. 13 and 17, which show the release relay l5 and associated parts of the cirpresent invention, the relay proper is of a well known type, commonly referred to as a telephone relay. On the core I5 is assembled a low resistance coil 20 of a comparatively few turns concentrated at the armature end of the core. Next in order is a high resistance winding 2| of several thousand turns, occupying the central part of the core length. At the heel end of the core is assembled'a concentric sleeve or slug of copper 23. The coils 20 and 2| are wound in the same direction and the' adjacent terminals of the windings are connected together in series connection.

The release relay as thus far described is a well known type commonly classified as a doublewound slow releasing relay. When supplied with a pulse of sufficient magnitude and of considerable duration, such relays normally operate in from .004 to .006 second, and release in from .08

to .28 second after being fully energized. In high is speed printing telegraphs, however, the signal impulses are of very short duration, the complete pulse interval being of the order of "-003 to .005

second. A relay of the usual type designed to have a release time of .25 to .30 second, i. e. the time required for the distributor arm to make one revolution, plus a margin, will not respond to impulses of short duration, for the reason that the copper slug required to produce such delay in release time is of comparatively large size, and prevents by its reaction the storing of the required amount of magnetic energy in the magnetic structure of the relay. To overcome this difiiculty, which is inherent with this type of relay, a storing condenser 22 is connected in shunt across the terminals of the high resistance winding 2|. This condenser should normally be of considerable capacity, values of from 2 to 16 microfarads, depending on the release time desired, having been found to give good results. with this condenser added to the combination, the operation of the release relay IS in response to current impulses of short duration is'as follows: When the synchronizing pulse is applied to the circuit shown in Fig. 17, a rush of current flows through the low resistance coil 20 into the storing condenser 22, which because of its large capacity offerscomparatively little impedance to such rush of current, particularly at the beginning. This rush of current through coil 20 magnetizes the core I5 at the armature end and attracts the armature I6. The reaction of the high resistance coil 2| and the slug 23 are inefiective to prevent the coil 20 from magnetizing the armature end of the coil I5, because of their remoteness from this section of the core, and because of the high inductance of the coil 2|. The counter E. M-. F. generated by transformer action in coil 2| by the current in coil 20 does not oppose the current in coil 20, but is utilized to aid in charging condenser 22. The maximum energy is thus stored in the charge of condenser 22. On the decay of the pulse current, this energy, combined with that 1 stored in the coil 2| and the slug 23, operate to maintain the magnetic flux in the core, in accordance with Lenzs law. The armature is thus held firmly to the core during the decay of the pulse and thereafter. The release time is controlled by the amount of charge on the condenser 22 and the time required for the current through coil 2|, due to this charge, to decay until the holding current in the coil 2| drops below minimum value. The variable resistor I9, located in the circuit as shown in Fig. 17, provides a convenient means for adjusting electrically the release timeof the relay without the necessity of change in design, or mechanical adjustment of the relay. It is to be noted that the location of resistor IS in the circuit is such, as not to interfere with the operating pulse, but acts only to retard the discharge of condenser 22 through the coil 2I-. Where such adjustment of the release time is not required, the resistor 22 may be omitted without detriment, provided the resistance required to produce the release time desired is incorporated in the coil 2|.

It is to be noted that the role of the slug 23 is materially different in the present invention from that played in the types of slow release relays heretofore known. 'In such prior types, the

release time is mainly dependent on the energy induced in the slug' (stored in the form of circulating current) by change in the magnetic flux in the core I5. In the present invention, the release time is controlled almost exclusively by the charge on the condenser 22 and the characteristics of the coil -2 I, any contribution from the slug being inconsequential. For certain values of capacity of the condenser 22 and of inductance and resistance of the coil 2|, an oscillatory discharge of energy between the condenser 22 and coil 2| may occur. For other combinations, a reversal of flux may occur when the circuit including the windings of the release relay is broken. In such instances the relay may release the armature I6 momentarily, causing an unwanted drop out. The slug 23, by its damping action, opposes sudden magnetic changes, and causes the relay to hold without chatter or release during transient conditions in the circuit. The damping action of the slug 23 is of importance in cases where the relay tends to. chatter or drop out momentarily. In cases where such tendencies do not exist, the slug 23 may be dispensed with. I

The relay describedis capable of quick operation when supplied with impulses of short duration; of holding firmly over periods of as much as a second after the energizing current has been cut oil; and of being reenergized by short current pulses recurring periodically. It is further characterized by the principle of storing the energy forholding the relay in an operated condition is an associated condenser, which condenser is charged partly by the pulse current'and partly by energygenerated in the holding winding by transformer action from the operating winding. The characteristics and principle of operation of this relay are such as to constitute a generic class distinguished from prior forms of quick acting, slow release relays. 1

The motor governor Referring to Figs. 18 to 21 inclusive, the motor governor I00 which is of the electrical type,

consists of a disk IOI of insulating material,

mounted on a hub I02, which in turn is mounted on the motor shaft I03 by set screw I04. On the periphery of the disk IOI are mounted two slip rings, I04 and I05, by which means current is v upturned portion of the bracket I01 is threaded the adjustable contact screw III having at the end a contact I I2.

The governor bracket I08 mounts the kinetic members, namely, the tongue H3 and the governor spring Ill. The tongue H3 is ofspecial construction, consisting of .a flexible strip 5, and a. bi-metal strip IIB secured together by rivets In, as shown (see Fig. 20). As is well known, bi-metal consists of sheets of two metal or dissimilar co-eflicients of expansion, usually welded together to form one laminated sheet or strip. It has the property of exhibiting curvature when heated, the degree of such curvature being to a certain extent proportional to the change in temperature from the particular temperature at which the bi-metal is fiat or straight. Metals commonly used in producing bi-metal are brass and steel, and brass and Monel metal.

At the outer end of the bi-metal strip H6 is mounted the movable contact 8', positioned to lie fiat against the stationary contact II2 when their surfaces are in contact. The ton ue II! is conveniently mounted on a support I20 by means of a screw l2l and clamp I22. The support I20 is part of the governor bracket I08. Near the middle of the tongue is a hole into which is inserted the swivel pin I23, having a hole into which is threaded one looped end of the governor spring Ill. The governor bracket I is mounted on the disk MI by two screws H9 at one end, which screws terminate in the slip ring I making electrical contact therewith. The contact bracket I01 and the governor bracket I08 are insulated electrically, except when the contacts I I2 and H8 are closed. A portion of the governor bracket I08 is upturned to form the support I24 upon which is mounted the flexible adjusting lever I25. The free end of the adjusting lever is turned inwardly and is perforated by a small hole into which is threaded a looped end of the spring I I4 as shown. Between the bent portion of the adjusting lever I25 and the support-.124, the adjusting lever is pierced by a hole, through which is assembled the micrometer adjusting screw I26, screwed into the support member I21,

The operation of the governor is as follows: Assume that the governor is rotating in a counterclockwise direction as viewed in Fig. 18. At a particular speed, the centrifugal force on the tongue 3 will exceed the spring tension in the spring H4, and the contacts II2-II8 will open. When these contacts open, the resistance R2 is inserted in series with the motor as shown in Fig. 21. The motoris thereby slowed down, causing the contacts to close, again speeding up the mo tor. This process is repeated many times a second, the motor not reachinga stable speed, but varying minutely above and below the speed at which the. contacts open. This type of governor, is well known, and it is to be observed that both the inertia of and centrifugal force on the tongue II3 contribute to the regulating action. It has therefore been called a centrifugal-inertia governor. It is characterized by its sensitivity and accuracy of regulation.

The novel-features of the present invention reside in the means for temperature compensation and for minorspeed adjustment. It is evident that the tension in the spring H4 determines the speed to which the motor is regulated. An increase in the temperature of spring I I4 results in a slight decrease in its tension, lowering slightly the regulated speed of the motor. This effect is compensated for in two ways. The governor bracket I08 is held in position at one end by screws I I9, the other end being free to move endwise only. The tensioning lever I25 and the adjusting screw I26 are mounted at the free end of the governor bracket I08. As the temperature of the governor increases, the governor bracket I08 is extended endwise by thermal expansion, stretching to a slight extent the spring I I4, thereby increasing its tension and compensating in part for the decrease in tension due to tempera ture. The compensation gained by this means is limited, however, by the thermal expansion of the material of the governorbracket along its 'length, and since the length of wire in the spring is much greater than the length of the governor bracket, compensation over a considerable range of temperature is not readily accomplished by this means alone. The second temperature compensation means is provided by the bi-metal strip II6 forming part of the tongue II3. As shown in Fig. 20, in exaggerated form, when the temperature of the bi-metal strip H6 is increased, it curves convexly outward. Due to this curvature, the tension of the spring I I4 is increased with increase of temperature, compensating for its normal loss of tension with increase of temperature. By using proper bi-metal combinations and proportions of parts, determinable by well understood methods, thermal compensation of the governor may be accomplished over a considerable range of temperature. With this improvement, the type of governor shown will regulate the speed of the motor with a high degree of precision under various conditions of temperature.

Minor speed adjustments It would appear that the resistance R2, commonly called the gap resistance, if sufliciently large to slow the motor down to the speed set by the governor, would have little 'efiect on the speed set by the governor. Such is the case, but a minor change in speed doesresult from a comparatively large change in the value of the resistance R2. According to the present invention, this effect is utilized to accomplish minor adjustment of the motor speed, without mechanical adjustment of the governor, the value of R2 being variable for that purpose.

It is to be noted that changing the value of the gap resistance R2 is not equivalent to introducing a similar resistance into other parts of the motor circuit. Resistance placed in series with the motor, for example, has the same effect as a change of load, and is counteracted by the governor. The effect of such series resistance is also to impair the range of regulation of the governor. A relatively large change in the gap resistance R2 does not limit to any material extent the range of regulation of the governor, but does produce a minor change in the speed set by the governor.

In printing telegraph systems, it is sometimes desirable to cause the sending instrument to run slower by a constant amount than does the receiving instrument, or vice versa In the present invention a change in the gap resistance is utilized to effect the desired constant speed diflerence. For this purpose, as resistance RI is placed in series with the variable gap resistance R2 but is normally short circuited by the contacts I 09-I09. When these contacts are closed, the motor speed is regulated by the governor gap re-. sistance R2 as previously described. When the contacts are open, additional resistance is introduced in. the gap, and minor but constant decrease in speed results. It is obvious that the same arrangement, considering as normal the speedwhen contacts IDS-I09 are open, will produce a minor increase in speed when the contacts IDS-409 are closed. The contacts IDS-I09 may consist of a switch, for local operation, or of the contacts of a relay for remote control.

It is thus clear that the present invention provides a novel method of temperature compensation and minor speed control and adjustment for an electrical governor. The improved governor herein described is highly accurate, rapid and sensitive in action, self-compensating for temperature changes, adapted to minor speed adjustments without stopping the governor or changing its mechanical adjustments, and particularly adapted to control of incremental speed changes by remote control.

Spring link feature As previously stated, the signal impulses and operation impulses in a high speed printing telegraph are very brief in duration, and special provisions are necessary to assure certain response of relays and magnets to such brief impulses.

One of the features of the present invention 15

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