US2120235A - Teletypewriter system - Google Patents

Description

June 14, 1938. .1 F. BEAT-HE ET AL TELETYPEWRI TER SYS TEM Filed Jan. 2, 193e 2 sheets-sheet 1 J. FS BEA T 77E /N VEN TOPS H. J. CUNNINGHAM WRROYCROFT .BV I

ATTORNEY.

.Iu'ne 14, 1938. J'. F. BEATTIE ET-AL TELETYPEWRITER SYS 2 Sheets-Sheet 2 Filed Jan. 2, 193ey JJBEATT/E /NVENTORS H. J. C UNN/NGHAM W. R. ROVCROFT A 7` TOPNE V Patented June 14, 1938 UNITED STATES PATENT OFFICE 'rELETYrEwmTEa SYSTEM Application January 2, 1336, Serial No. 57,268

7 Claims.

I I'his invention relates to teletypewriter systems and, more particularly, to systems which include a teletypewriter having contacts for performing various functions.

It is an object of this' invention to mount contacts for performing various functions, in a teletypewriter to be operated by the teletypewriter mechanism. A

It-is also an object of this invention to open and close, by means of a central teletypewriter, telegraph lines leading from a teletypewriter ofce to other teletypewriter stations.

It is a further object of this invention to providea central teletypewriter oiiice with an improved switching device for switching various circuits.

It is an additional object of thisinvention to enable a subscriber at a teletypewriter station to connect his teletypewriter through a teletypewriter central omce to another teletypewriter station without the assistance of an `operator at the central office thereby eiecting 'a saving in operating time.

It is a further object of this invention to enable subscribers having their lines connected together at a central oilice to disconnect their connection at the central oice without the assistance'of an operator at the central oiiice thereby effecting a further saving in operating time.

rlhese` and other objects of the invention are attained by means of a plurality of contacts mounted in a teletypewriter at various predetermined positions." The contacts are adapted to be operated by the teletypewriter mechanismin response to certain preassigned teletypewriter signais which may, if desired, be sent fromother teletypewriter stations. In the preferred embodi- V ment of the invention, the operation of the contacts serves to operate relaysjwhich operate and lock-up to perform any desired function, such as switching telegraph circuits. Also in the preferred embodiment of the invention, the operation of a particular contact unlocks the switching relays and causes them to deenergize thereby restoring the system to its normal condition. If desired, these relays may be designed to perform a variety of functions, such as switching on and .off a teletypewriter motor at an outlying tele- .typewriter station.

These and other features of the invention now be described in detail with reference tothe drawings in which Figure 1 represents a teletypewriter central ofce and shows a schematic diagram in perspective'of a teletypewriter provided with special con- (Cl. ITS-2) tacts and circuit `connections leading to the switching relays; and

Fig. 2 shows the switching relays at the central oilice and the telegraph lines leading to the other teletypewriter stations.

The teletypewriter T, shown in Fig. 1, is similar to the teletypewriter disclosed in Patent' ,1,745,633 granted February 4, 1930 to S. Morton et al. The disclosure of this Morton et al. patent is incorporated herein by reference as a part of this specification. However, the invention is.r

not limited to this type of teletypewriter nor is it limited to the speciiic structure shown in the drawings which is a preferred embodiment of the invention and is shown andvdescribed in order to illustrate A and explain the features and principles of operation of the invention.

For purposes of illustration, `teletypewriter T,`

which is shown to be in its upper case position, is represented as being located at a teletypewriter central oiiice although it may be located at an ordinary teletypewriter station if desired. Con- I nected to this central oiiice by telegraph lines L1 to Le, inclusive, are the subscribers teletypewriter stations S1 to Se, inclusive, each of which is provided with a teletypewriter T1 to To, inclusive, and a teletypewriter motor M1 to Ms, inclusive. Each of the motors M1 to Me, inclusive, is operated by an individual power supply source B1 to Bs, respectively. At stations S1, S2, and Ss theA energizing circuits leading fromthe respective local vpower supply sources to the motors are opened and closed by manually operable switches A1, A2, m, and A5, respectively, controlled by the local attendant 'at each station.

The energizing .circuit of the motor M4 is nor- ,June 13, 1933 to W. Daum. The disclosure of this mally open at the armature and contact A4 of thej normally unoperated relay 43.A This energizing circuit is adapted to be opened andA closed by any- Daum patent is incorporated herein by reference as a part of this specication. The energizing circuit of motor Ms is normally open at contact Aa of relay R4 located at the central oflice. It is to be understood that these diiferent motor con-- trol circuits maybe varied as desired to meet the particular requirements of a given system and that they are shown here for the purpose of illustrating the wide extent to which the invention may be applied. 1t should also be understood that theinvention vis capable of use with any other type of line circuits. such as duplex circuits.

The teletypewriter T at the central oice'has a motor M which is operated by a power supply source B over an energizing circuit closed by a manually operable switch lever A. Motor M operates teletypewriter T by means of gears G1 and G2 which alternately raise and lower the printing bail I9 to operate the pull bars selected by the selecting mechanism I8 as is described in the Morton et al. patent. Mounted in the teletypewriter T is one normally closed contact C and six normally opened contacts C1 to Cs, inclusive. Contacts C1 and C4 are operated by portions of the teletypewriter mechanism only in response to the reception by the receiving magnet R of upper case teletypewriter signals. Contact C is operated by a pull bar I1 which may, if desired, be selected by the selecting mechanism I8 only in response to the reception of a preassigned upper case code combination of signals. Contacts C2, C3, C and C6 are each designed to be operated, in this particular embodiment of the invention, by pull bars I2, I3, I5 and I6, respectively, in response to the reception of both upper and lower case signals. However, since these contacts C2, C3, C5 and Cs are connected in series with contact C7, which is designed to be closed only when the platen 21 is in its upper case position, they will only be effective to perform their switching functions when the platen 21 .is in its upper case position. Thus, the pull bars I2, I3, I5 and I6 associated with these contacts can be used for performing their normal lower case functions.

In the operation of the system, let it first be assumed that the subscriber at station S1 Wishes to connect himself through the central oflice to the subscriber at station S3. The subscriber at station S1 normally has his switch A1 closed during business hours so that his motor M1 is energized by his local power supply source B1. Accordingly; the subscriber, by means of his teletyewriter T1, rst transmits a gures shift signal out over line L1, conductor 20, line L2, through station S2, line Lz, conductor 2|, through the normally closed contacts of. relay Rz, conductor 22, through the normally closed contacts of relay R11, conductor 23, sending contacts 26', conductor y I0, receiving magnet R, conductor 8, outer left armature of normally unoperated relay R4, and then to grounded battery 24. The shift signal transmitted -over this path energizes the receiving magnet R which operates the selecting mechanism I8 to select the gures pull bar 41 which is then elevated by the printing bail I9. In rising, pull bar 41 causes its extension 48 to elevate the left end of bell crank 49. This causes the right end of bell crank 48 to dip down thereby releasing latch 50. The release of latch 58 allows spring 5I to pull the platen assembly 52 forward. In moving forward, the platen assembly 52 pulls lever 28 forward suiliclently to remove slot 15 from the path of travel of extension 28 of the so-called blank pull bar I4. This places the platen assembly 52 and its associated apparatus in the upper case position so that this apparatus is now in the condition shown in Fig. 1.

The subscriber at station S1 now transmits a preassigned code combination of significant current variations which in this preferred embodiment of the invention, is known as a blank" signal. Upon being received at the central oflice, the blank signal causes the selecting mechanism I8 to select pull bar I4. Accordingly, the printing bail I9 elevates the pull bar I4 with the result that extension 29 of pull bar I4 will engage with lever 28 and raise it up. This elevates the left select pull bar 53.

end of lever 38 and, consequently, lowers the right end of this lever 30 thereby allowing spring 3| to pull down the left end of lever 32. As a result, the right end of lever 32 is raised and allows the spring contact C4 to close. This closing is only momentary because pull bar I4 is soon lowered by bail I9 and spring 11 then pulls lever 28 back into the position shown in the drawings.

The closing of contact C4 momentarily closes the energizing circuit of relay R4 from grounded battery 33 through the winding of relay R4, conductor 4, contact C4, conductor 9, conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 36, and then to ground 31. As a' result, relay R4 becomes energized and operates both its armatures. Before' contact C4 opens, relay R4 locks-up over a circuit from grounded battery 33, through the winding of relay R4, inner left armature, conductor 34, conductor 1, through contact C, conductor 35, conductor 36, and then to ground 31. At the same time, the communication circuit is switched from grounded battery 24 to the joining conductor 38 and then to conductor 39, out over line Lc to station Se, over line L6, conductor 40, line La, and then to station S3.

Since the subscriber at station S3 normally has his switch A3 closed during business hours, his motor M3 will be energized at this time by his local power supply source B3. Accordingly, the system is now in condition for communication to take place between the subscriber at station S1 and the subscriber at station S3. Significant current variations transmitted by the teletype- Writer T1 will travel over line L1, conductor 20,v

line Lz, through station S2, line L2, conductor 2|, conductor 22, conductor 23, sending contacts 26, conductor I0, receiving magnet R, conductor 8, conductor 38, conductor 39, line L6, through station Ss, conductor 40, line L3, and then to station Sa.

When the subscriber at station S1 wishes to eiect a lower case selection, he transmits the socalled letters shift code signal for causing the selecting mechanism I8 of teletypewriter T to Upon being elevated by the printing bail I9, pull bar 53 elevates its extension 54 which correspondingly elevates the left end of lever 55 which depresses the right end of lever 55. -When the right end of lever 55 is depressed, it causes the left end of bell crank 56 to be correspondingly depressed, which causes the top end of bell crank 56 to move backward to the rear of the teletypewriter. 'Ihis acts as a lever to pull back the platen assembly 52. In traveling to the rear of the teletypewriter T, the platen assembly 52 causes latch 58 to also move to the rear of the teletypewriter T with the result that latch 58 will engage with the catch in the right end of bell crank lever 49 thereby holding the platen assembly 52 in this position and preventing spring 5I from' pulling it forward. Thus, the platen assembly 52 is latched in its lower case position.

Since both stations S4 and Ss'are disconnected from the communication circuit at the armatures of relays R1 and R2, respectively, neither teletypewriter T4 nor teletypewriter T5 will record the signals sent from teletypewriter T1 at this time. Teletypewriter Ts will also not record these signals due to the fact that the energizing circuit for its motor Ms is open at contact As of relay Re. However, with the system in the condition shown in the drawings, teletypewriter T2 will follow the signals transmitted by teletypewriter T1 because the energizing circuitfor its motor M2 is closed at switch A2. If the subscriber at station S2 finds that the message being transmitted from station S1 to station S3 is of no interest to him, he can open switch A2 which will shut down his motor M2 with the result that his teletypewriter T2 will not now record vthe signals being transmitted.

Thus, the subscriber at station S1, which mair be located at a remote point, has connected hims elf through the central oice to the distant subscribers station S3 without any assistance from an operatorat the central oiiice. In other words, the subscriber at station S1 has switched both his and the other subscribers lines 8 and 39 from their terminations at batteries 24 and 25 to the joining conductor 38 thereby switching the line conductors 8 and 39 together. Consequently, a considerable saving in operating time is" effected since the subscriber at station S1 simply transmits the upper case code combination assigned to select pull bar I4 which closes contact C4 to operate relay R4 which immediately switches the two lines 8 and 39 together without any act by an operator at the central oflice. This saving in operating time is of importance in certain types of business where time is of the essence and promptness in putting calls through is essential.

AWhen the subscribers at stations S1 and Sa have nished communicating with each other, either one of them may effect a disconnection of their lines 8 and 39 at the central oiice by transmitting a preassigned telegraphic signal from either station S1 or station S3. This signal is received by the receiving magnet R at the central oiiice which accordingly operates the selecting mechanism I8 to select pull bar I1. `Bail I9 then elevates pull bar I1 thereby momentarily opening the normally closed contact C. 'I'he opening of contact C opens the locking-up circuit of relay R4: Consequently, relay R4 releases its armatures and switches the line conductors 8 and 39 from the joining conductor 38 to batteries 24 and 25 thereby disconnecting stations S1 and S3 from each other and restoring the system to its normal condition. If desired, the subscriber at station S2 may also eiect this disconnection. Since this disconnection is accomplished by any of the connected subscribers without the assistance of an operator at the central oice, a further saving in operating time is effected.

The nature of the business of the subscriber at station S1 may be such that it would be desirable for him to send a message to both the subscriber at station S3 and the subscriber at station .Se (which may, for example, be an outlying station near the central oce) and have the message recorded practically simultaneously by the teletypewriters T3 and T6. To accomplish this conference connection, it is first necessary to start the teletypewriter-motor Ms at station Ss by energizing relay Re. Accordingly, the subscriber at station S1 transmits a shift signal for selecting pull bar 41 to eiect the release of latch 50 to allow the platen` assembly 52 to be pulled forward by spring 5I. In moving forward, the platen assembly 52 carries latch 50 forward along the top edge of bell crank 49 thereby forcing down the right end of bell crank 49 to close contact C1. Consequently, contact Cv remains closed during the time that the platen 21 remains in its upper case position.

The subscriber at station S1 next transmits a preassigned combination of code impulses out over line L1, conductor 20, line L2, through station Sz, conductor 2l, conductor 22, conductor 23, sending contacts 26, conductor I6, receiving magnet R, conductorj 8, and. then to g/rounded battery 24. This code combination will cause the selecting mechanism I8 of teletypewriter T to select pull bar I6 which will then lbe momentarily i operated by the printing bail I9 to close contact -Ce momentarily. A path for energizing relay Rs is now closed from grounded battery 4I, through the winding of relay R6, conductor 6,

through contact C6, conductor 16, conductor 42,-

through contact Cv, conductor 44, conductor 36, and then to ground 31.

, As a result, relay Re operates its armatures and locks-up through a path from battery 4 I through the winding of relay4 Rs, operated left armature, conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 36, and then to ground 31. At the same time, the right armature of relay Re is operated and closes a path from power supply source Bs at station Se, over line conductor 45, operated armature and contact Ae of relay Re, line conductor 46, motor Ms, and then back to power supply source. Bs thereby energizing motor Ms and starting it into operation. The subscriber at station S1 then transmits the code signal for selecting pull bar I4 in the teletypewriter T at the central ofce. When bail I9 elevates pull bar I4, contact C4 is momentarily closed and relay R4 operates its armatures vand locks-up in the manner described above.

As soon as the platen assembly 52 moves back to its lower case position, the right end of bell crank 49 will. be elevated sufficiently to allow contact C'z to open. However, this has no effect on the switching relays R4 and R6 because these relays are locked up through the normally closed contact C.

Messages now sent from stationl S1 will pass through station S2, through the central oflice, and then through stations Se and Sa. The messages will thus be recorded practically simultaneously on both the teletypewriters T3 and Ts. They will also be recorded on the teletypewriter T2 at station Szprovided the subscriber at this station has his switch A2 closed. The subscriber at station S3 can transmit messages to any of the connectedstations and these messages will ybe lpractically simultaneously recorded by the teletypewriters T1, T2 and Ts. Likewise, the subscriber at station Ss can also send messages which will be recorded on any of the connected teletypewriters.

At the close of communication, any of the subscribers at stations S1, S3, or Se may disconnect this conference connection by transmitting the code signal assigned to select pull bar I1 at the central oftice which will momentarily open the normally closed contact C as was described above. The opening of contact C will open the locking-up circuits of both relays R1 and Rs and will cause them to release their armatures. This switches the communication circuit from conductors 8 and 39 vto batteries 24 and 25 Las was described above. At the same time the energizing circuit of motor M6 is opened at the contact Ae of relay Re. Consequently, motor M6 stops running. The system is thus restored to its normal condition.

' In the event that the subscriber at station S1 wishes to communicate with the subscriber at 4station S4 (which may, for example, be an outlying station near the central oiiice), he will transmit the shift signalto cause the platen 21 to be shifted to its upper case position as shown in the drawings. The subscriber will then transmit a preassigned upper case code signal Which. upon being received by the receiving magnet R, will effect thel selection of pull bar II by the selecting mechanism I8 of teletypewriter T. The elevation of pull bar II by bail I9 will, by means of the ratchet 51 and gear 58, drive the top of type bar 59 downward in an arcuate path. Bar 59 Will then hit lever 60 thereby tilting downward the right end of lever 6I. This drives the top end of lever 6I to the right and allows spring 62 to pull down the right end of lever 63 into latching engagement with the top end of lever 6I. Consequently, the left end of lever 63, which is normally located immediately beneath the printing bail I9, as shown in the drawings, is driven upward to close contact C1 momentarily.

The closure of contact C1 closes a path from grounded battery 64, through the winding of relay R1, along conductor I, through contact C1, conductor 65, and then to ground 31. Consequently, relay R1 operates both its armatures and locks-up through its right armature over a path from grounded battery 64, Winding of relay R1, operated right armature and contact of relay R1, conductor 34, conductor 1, normally closed contact C, conductor 35, conductor 36, and then to ground 31. It is necessary that relay R1 be designed to lock-up quickly because, when the reciprocating bail I9 comes down, it strikes the left end of lever 63 thereby knocking the right end of lever 63 up out of latching engagement with the top end of lever 6 I This permits contact C1 to resume its normally open position.

The operation of the two left armatures of relay R1 opens the normally closed left contacts of relay R1 and closes a path from conductor 22, over the inner left armature of relay R1, conductor 66, line L4, through station S4, backover line L4, conductor 61, outer left armature of relay R1, conductor 23, sending contacts 26, conductor I0, magnet R, conductor 8, and then to grounded battery 24. The subscriber at station S1 now transmits motor start signals, such as those described in the Daum patent mentioned above, which effect the energization of a relay 43 at station S4, similar to the motor control relay disclosed in the Daum patent. Upon being energized, motor control relay 43 operates its armature to close the contact A4 thereby closing the energizing circuit of motor M4 and starting motor M4 into operation.

Communication may now take place between stations S1, Sz and S4, the signals passing out over line L1, conductor 20, line L2, through station S11, conductor 2l, conductor 22, conductor 66, line L4, through station S4, conductor 61, conductor 23, and then to grounded battery 24 as was described above. These signals will also pass through the receiving magnet R. It might be mentioned here that this is the case with all connections between the various subscribers stations; that is, receiving magnet R follows all the signals sent between these stations.

At the close of communication, any of the subscribers at the three connected .stations S1, Sz, and S4, may send the code signal for selecting pull bar I1 which momentarily opens contact C, as described above, with the consequent opening oi' the locking-up circuit of relay R1. Relay R1 now releases its armatures, thereby opening the circuit leading to station S4 and connecting conductor 22 directly to conductor 23 without passing through station S4. Incidentally, the motor at station S4 may be stopped by any of the subscribers in the manner described in the Daum patent. It .might also be stated here that the central office operator can eii'ect any of'the disconnections between any of the subscribers stations because' her sending contacts 26 are always connected in series with the communication circuits. This circuit construction can be modified in accordance with the requirements of different systems.

If the subscriber at station S1 wishes to send a message to be recorded by the teletypewriters 4T3 and T4 at stations S3 and S4 (leaving station Sz out of consideration for the sake of simplicity) hewill send the code signals to select pull bars I I and I4 for closing contacts C1 and C4. This will operate relays R1 and R4 which will lockup as described above to close the lines leading to stations S3 and S4. Any of the connected subscribers may disconnect this conference connection by sending the code signal to select pull bar I1 for opening contact C. This opens the locking-up circuits of both relays R1 and R4 thereby restoring the system to its normal condition.

Also, if the subscriber at station S1 Wishes to send a message to be recorded by the teletypewriters at each of the stations S1, S4 and Ss ,(again leaving station S2 out of consideration for the sake of simplification) he will follow the same procedure as that outlined in the preceding paragraph except that he will, in addition, send the code signal to select pull bar I6. The operation of pull bar I6 will close contact C5 and operate relay R5 which will lock-up and close the energizing circuit of motor Ms at station S5 thereby conditioning station S6 for the reception and/or transmission of messages. Any of the connected subscribers, or the central oiice operator, may disconnect this conference connection in the manner described above.

Likewise, the subscriber at station S1 may connect himself through the central office to the station S5 by first transmitting the shift signal for shifting platen 21 in teletypewriter T to its upper case position thereby closing contact C1. The subscriber at station S1 then transmits the preassigned code combination for selecting pull bar I2. The elevation ofv pull bar I2 by bail I9 closes contact C2 thereby closing the energizing path for relay R2 from grounded battery 68 through the Winding of relay R2, conductor 2, contact C2, conductor 42, contact C1, conductor 44, conductor 36, and then to ground 31.

Upon being energized relay Rz operates its armatures and locks-up from battery 68, through the winding of relay R2, operated left armature,

.tery 24. If a conference connection is desired,

other stations may be connected into the communication circuit in the manner described above. At the close of communication, any of the connected subscribers may disconnect the connection by eiecting the operation, or opening, of the tion as has been described above thereby closing contact C1. 'Ihen the upper case code combination is transmitted for selecting pull bar I3 which, when operated by bail I9, momentarily closes contact C3 to enable relay Re to operate over a path traced from grounded battery 1l. through the winding of relay R3, conductor 3, contact Ca, conductor 12, conductor 42, through contact C1, conductor 44, conductor 36, and then to ground 31.

Upon being energized, relay R3 operates its armatures and'locks-up over a path from grounded v battery 1 I through the winding of relay R3, operated left armature, conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 36, and then to ground 31.' In operating its right armatures, relay R3 will perform the desired switching function. When it is desired to discontinue the switching operation, the code signal is sent for causing pull bar I1 to open the normally closed contact C which opens the locking-up circuit of relay R3 thereby causing its release and restoring the `system to its normal condition.

If it is desired to perform still other switching functions, they may be eifected by shifting the platen 21 to its upper case position to again close contact C1. The upper case code combination for selecting pull bar I5 is then transmitted. The operation of pull bar I5 closes a path from grounded battery 13, through the winding of relay R5, conductor 5, contact C5, conductor 14, conductor 42, contact C1, conductor 44, conductor 36, and then to ground 31 thereby energizing relay Rs. Upon operating its armatures, relay R5 will lock-up over a path from groundedbattery 13,

through the winding of relay R5, operated left armaturef conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 36, and then to ground 31. In operating` its right armatures, relay Rs will perform the desired switching functions. When it is desired to terminate this switching operation, the signal for effecting the opening of the normally closed contact C is transmitted thereby opening the lockingup circuit of relay'Rs which now releases its armatures and restores the system to its normally unoperated condition.

Whereas the operation of the system has been described principally with reference to connections originating from the dominant station S1, it is to be understood that these connections may be effected and disconnected in a similar manner by the subscriber at the other dominant station Sz. It is to be. further understood that other dominant stations may be added to the system according to the particular requirements of an' individual system.

For the purpose of illustration, contact C1 has been shown to be operable only by an upper case code combination by means of a particular arrangement of the teletypewriter apparatus which obviates the necessity for having contact C1 in series with the platen contact C1. If it is desired to have levers 60, 6I and 63 perform some other function, contact C1 may be mounted above a pull bar and connected in series with the' contact C1 the same as contacts Cz, Ca, C5, and Cs. The same applies to contact C4 which has also been shown to be operated in response to a particular upper case code combination due to a particular arrangement of the teletypewriter apparatus. If it is desired to have levers 28, 30 and 32 perform some other function, this may readily be done by placing contact C4 above a pull bar and connecting it in series withthe contact C1 the same as contacts C2, C3, C5 and Cs. Contact C may be arranged to be operated in response to the reception of either an upper or a lower case code combination. It may be preferable r'to design the selecting mechanism of teletypewriter T in such a manner that pull bar I1 will only be selected in response to an upper case selection. Thus, by means of this invention, the various pull bars of the teletypewriter 'I at the central office may be used for performing their regular printing functions in response to lower case selections. The restriction of the switching functions of the pull bars to upper case selections thereby facilitates regular communication between the stations. Otherwise if the pull bars were not connected in series with the platen contact C1, whenever the pull bars were operated, they would close their contacts to operate the particular switching relays associated therewith.

It is to be understood that this specific application of the invention has been shown and described for purposes of explaining the principles and features of operation of the invention. Many changes may be made in the construction shown without exceeding the scope of the invention. More switching contacts to be operated by the pull bars of the teletypewriter at the central ofce may be added whenever desired to perform any functions that may be required. Likewise, the circuit connections of the various subscribers stations may be varied as desired to meet the requirements of any particular communication system. In short, the scope of the inventionis to be limited only by the claims appended hereto.

What is claimed is:

1. A teletypewriter having pull bars, selecting mechanism for selecting certain of the pull bars,

a reciprocating bail for elevating those pull bars selected by the selecting mechanism, switching contacts located in the teletypewriter above the pull bars and adapted to be selectively operated vindividually by the pull bars when the pull bars cated in the teletypewriter for discontinuing the effect of the operation of any one of the switching contacts following the operation of the control contact.

2. A teletypewriter bination a teletypewriter central ofllce having a teletypewriter with a platen assembly provided with an uppercase position and a lower caseV position, shift mechanism for shifting the platen Vfrom one of said positions to the other, a plurality of telegraph lines, a plurality of teletypewriter stations connectable to the central olce' by the telegraph lines and normally disconnected from each other, normally ineffective instrumentalities for enabling an operator at one of the teletypewriter stations to connect himself through the central oiiice to one of the other` teletypewriter stations, a control contact located in the teletypewriter at the central oflice for consystem including in com- -ditloning said instrumentalities for effective operation, and means operating in response to the operation of the platen assembly for operating said control contact.l l

5 3'. A teletypewriter system including in combination a teletypewriter central oice having a teletypewriter with a platen assembly provided with an upper case position and a lower case posi'- tion, shift mechanism for shifting the platen l from one of said positions to' the other, a plurality of teletypewriter stations connected to the central oflice by a plurality of telegraph lines,

`normallyvunoperated switching apparatus at the central oiice for switching said telegraph lines l together, and -a control contact for conditioning the switching apparatus for operation in response to the reception by the teletypewriter at the central office of permutation code signals of a preassigned case transmitted over one of the lines by one of the stations.

4. A teletypewriter system including in com- `bination a central oflice having a teletypewriter with a plurality of pull bars and a platen assembly provided with an upper case and a lower case position, shift mechanism for shifting the platen from one of said positions to the other, a plurality of subscribers teletypewriter stations, a plurality of communication lines extending from the subscribers stations to the central oilice but normally disconnected from each other, switching means for selectively connecting the communication lines together at the central oice, said switching means including contacts mounted ,in the teletypewriter at the central oflice for operation by the pull bars, a control contact for controlling the effectiveness of the operation of said contacts, and means for operating said control contact in response to the reception by the teley typewriter at the central oiiice of permutation code signals of a preassigned case.

` 5. A teletypewriter having shift mechanism, a pluralityof pull bars, selecting mechanism for selecting certain of the pull bars, a reciprocating.

ball'for operating those pull bars selected by the selecting mechanism, switching contacts mounted in the teletypewriter in operative relationship with the pull bars, circuits adapted to/.be opened and closed by the switching contacts, a normally open contact connected in series with said circuits whereby the operation of said contacts is normally ineffective, an instrumentality for closing said normally open contact for rendering the operation of the switching contacts eiective, and means for operating said instrumentality in response to the selection and operation of a preassigned pull bar. l

6. A teletypewriter system comprising in combination a teletypewriter central ofce having a lteletypewriter with a plurality of pull bars, a

plurality of teletypewriter stations connected to the central oice by a plurality of telegraph lines for the transmission and reception of signals, normally unoperated switching apparatus at the central office for switching said telegraph lines together, operating means for operating said switching apparatus, and a control contact mounted in the teletypewriter at the central of'- ce for rendering said operating means ineffective to perform any useful function.

7. A teletypewriter system including in combination a teletypewriter central oilce having a teletypewriter with a plurality of pull bars, operatingA means for operating the pull bars, a plurality of teletypewriter stations, a plurality of telegraph lines connecting the teletypewriter stations to the central oflce for the transmission and reception of signals, normally unoperated switching apparatus at the central oce for switching said telegraph lines together, operating means for operating said switching apparatus, a control contact mounted in the teletypewriter at the central oice for rendering said operating means ineffective to .perform any useful function, and. an instrumentality for closing said control contact in response to the operation of one of the pull bars and for opening said control contact in response to the operation of a diiferent JAMES FRANCIS BEATIIE.

HAROLD JEROME CUNNINGHAM. WALTER RICHARD ROYCROFT.

pull bar. y

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