Patent GB-522468-A (GB)
Title: Improvements in or relating to printing telegraph apparatus
IPC: H04L19/00
Filed: 1938-10-11
Abstract: 522,468. Type printing telegraphy. CREED & CO., Ltd., THOMPSON, A. E., and SALMON, R. D. Oct. 11, 1938, No. 29462. [Class 40 (iii)] Relates to associated transmitters and receivers for step-by-step type-printing telegraphy and consists mainly in the provision of means whereby when the typewheel of the receiver is given a specific position by a distinctive signal, such as an " end-of-message" signal, from another machine at a calling station, automatic means cause the transmitter to transmit the same distinctive signal, so that the reception back of this signal at the calling station indicates that the called station is in proper working order. Preferably this signal is similar to an " end-of-message" signal operating in the manner described in Specification 521,591. In the apparatus shown in skeleton, a keyboard transmitter of the kind described in Specifications, 490,404 and 502,521, is used. The " end-of-message " key lever KL is pivoted on a shaft PS and provided with a two-armed lever KA, KB. When the key is depressed the arm KB initiates the signal and the arm KA cooperates with an arm SP on a shaft SS to stop that shaft in a position corresponding to the key operated, in this case the " end-of-message" position. The arm KB bears on a bar LB of a frame pivoted on a shaft LBS and rocks that frame. This locks the keyboard and rocks a lever DL pivoted on shaft DLP, thereby releasing a detent DLL allowing a shaft DCS to rotate. After a predetermined rotation of shaft DCS, a clutch is set to transmit rotation to a cam shaft TCS, which actuates transmitter contacts not shown, until the shaft SS, which is geared to the shaft TCS, is stopped by the engagement of the arms SP, KA. The shaft TCS is driven through the clutch by gearing GS<SP>2</SP>, GS<SP>1</SP>, GS<SP>3</SP> from the main motor shaft MS, and the shaft DCS is driven through a clutch by the shaft DS of gear wheel GS<SP>1</SP>. The motor also drives through a coiled spring (not shown) the typewheel shaft TWS and the printing hammer shaft PHS in the manner described in Specification 490,361 ; and the printing hammer PH is actuated when the typewheel comes to rest by means of a cam PHC on the shaft PHS in the manner described in Specification 490,413. According to the invention, the typewheel spindle TWS is provided with a cam EMP which, when the typewheel is in the " end-ofmessage " position, engages with a selecting lever SL carried by the printing hammer PH and formed with an extension ESL co-operating with one end of an intermediate lever IL carried by an arm SA on a vertical spindle SVS carrying another arm TA engaged by an extension EKL of the key lever KL. The end of the arm SA co-operates with an escapement device ED controlled by an extension FOA on the printing hammer PH to allow the SA to be moved by a spring VSS step-by-step to bring the end of the intermediate lever IL in the path of the extension ESL. The other end of the intermediate lever IL co-operates with an arm FA on a vertical spindle FVS carrying other arms FIA, SIA co-operating respectively with latches L, HCL. The latch L is part of an arm C pivoted to a frame B which is pivoted on shaft PS and provided with arms TAL co-operating with key lever KL and cam RS on shaft DCS. The latch HCL hangs from a lever MCL pivoted on a shaft MCS and connected at its other end to a bell-crank lever MBC serving to close and open the contacts MC in the motor circuit. Another lever ABL also pivoted on shaft MCS is connected at one end to a bell-crank lever SBC serving to close and open contacts GC in an alarm circuit, and the other end of the lever ABL is provided with a latch AL. The latches AL, HCL normally rest on stops AST, MST and can be pulled off these stops by levers AAL, MHC on bell-cranks ALL, MHL. The bell-crank ALL is controlled by an " end-ofmessage " cam EMC on shaft SS, and the bellcrank MHL is controlled by a cam MOL on shaft DCS and by an arm MSL on the spindle MSS of a " motor-start " key MSK. The shaft MCS carrying the levers ABL, MCL is periodically lifted and lowered by lever mechanism SEL, SOL, oscillated by a cam SOC driven by reduction gearing from motor shaft MS, so that the latches AL, HCL are periodically lifted and can regain their seat on the stops AST, MST when the conditions permit. Operation of machine.-The operator at a calling station first depresses his " motorstart" key MSK. This, acting through mechanism MSS, MSL, MHL, MHC, pulls latch HCL off its stop MST, allowing mechanism MCL, MBC to close motor contacts MC. Then operator depresses his "end-of-message " key K, whereupon the message is transmitted to the called station and to the receiving apparatus of the calling station itself, where the motor contacts are kept closed by the co-operation of the cam MOL with the bell-crank MHL. At the calling station, the depression of the key K also acted through mechanism KL, EKL, TA, SVS, SA to withdraw end of lever IL from reach of extension ESL, lever IL remaining thus held away by escapement ED, so that when the typewheel reaches its " end-of-message" position and hammer PH is operated, lever IL and the mechanisms connected thereto are inoperative but escapement ED releases the arm SA one step towards bringing lever IL into engagement with extension ESL. At the called station, the arrival of the " end-of-message" signal causes the typewheel to be driven by the spring interposed between its shaft and the motor, which spring is maintained wound up. When the typewheel reaches its " end-ofmessage " position and the hammer PH operates, extension ESL rocks intermediate lever IL, and this through mechanism FA, FVS, FIA, SIA releases latches L, HCL. Release of latch HCL allows mechanism MCL, MBC to close motor contacts MC, and release of latch L allows mechanism C, B, TAL to depress key lever KL. The called station therefore retransmits the " end-of-message " signal it first received from the calling station. This retransmitted signal goes to the receivers of both the called and calling stations. At the called station, the intermediate lever IL being now out of reach of extension ESL, key lever KL is not depressed a second time, but escapement ED releases arm SA one step. At calling station, the typewheel is again rotated and the printing hammer repeats the message thereby indicating to the operator that the called station is in proper working order. This second operation of the printing hammer also causes escapement ED to release arm SA a second step, allowing intermediate lever IL to come within reach of extension ESL. The calling station is now ready to commence transmission of a message. The actuation of the printing hammer at the called station after receipt.of the first letter will cause escapement ED to release arm SA a second step, allowing lever IL to return to operative position. While a transmitter is being actuated, cam MOL acting through mechanism MHL, MHC, HCL, MCL, MBC keeps motor contacts MC closed ; but when transmitter is not actuated, the next operation of the cam SOC causing the lifting and lowering of shaft MCS brings latch HCL again on stop MST, causing motor contacts MC to be opened. Where each of several machines may operate with any one of a number of other machines, it is necessary to terminate every communication by an " end-ofmessage" signal. To ensure that this is done, an alarm device is connected to the contacts GC and is sounded except when the shaft SS is in the " end-of-message" position, in which cam EMC acting through mechanism ALL, AAL pulls latch AL off its stop AST, allowing contacts GC to be opened by mechanism SBC, ABL.