Patent GB-854086-A (GB)
Title: Communication equipment
IPC: H04L17/04
Filed: 1956-11-09
Abstract: 854,086. Driving magnetic tapes. SMITH-CORONA MARCHANT Inc. Nov. 9, 1956 [Nov. 16, 1955], No. 28453/59. Divided out of 854,083. Class 40 (2). [Also in Groups XIX and XL (b)] In apparatus for recording telegraph mark-space code combinations for use in the communication system described in Specification 854,083 (see Group XL (b)), utilizing an elongated magnetizable recording medium, the code elements of each combination are recorded in sequence across the tape by means of a head which is traversed across the tape whilst the tape is held stationary, and the medium is advanced an incremental distance between each recording operation. Potentials representing the code elements of each combination are presented to the apparatus simultaneously in separate channels and are transferred to the head in sequence by means of a commutator synchronized with the movement of the head. A converse procedure is employed for reproduction of signals from the medium, the commutator being employed to direct the elements appearing sequentially from the head into separate channels. Each step-by-step advancement of the medium is effected by means of an impulse in timed relationship with the code combination which actuates an electromagnet to release the apparatus to effect a cycle of operation. Recording medium.-The magnetizable medium comprises a polished spring steel tape 708 containing sprocket tooth holes 716, Figs. 40 and 41, along one edge and which is preformed by tensioning around a roller so that it has a natural tendency to coil. By virtue of this, the tape may be transferred back and forth between take-up and feed spools 706 and 704, Fig. 39, by means of only a tape advance sprocket 702 without the use of auxiliary driving means for the spools. The tape becomes arched as a result of the preforming and a spring-loaded pressure roller 714 is provided to flatten it as it passes under the recording head 712. An erase head 730 follows the recording head in the direction of tape movement employed for recording and reproduction. One end of the tape has a notch 719, Fig. 40, which is employed to operate a switch (see below) to signal that capacity for only five transverse recordings remains. A further notch 718 is provided to permit a mechanical trip and switch to operate (see below) to prevent the tape from being completely unwound from the feed spool. The other end of the tape has a notch 720, Fig. 41, which functions in a similar manner (see below) to prevent the tape from being completely unwound from the take-up reel during a rewind operation. Head traversing mechanism.-The recording apparatus, the complete construction of which is illustrated in detail in Figs. 44-49 and 51 (not shown), incorporates a normally stationary main shaft which is coupled to a continuously driven motor through a friction clutch and which may be released to make one revolution by an impulse applied to energize the electromagnet of a stop mechanism carried by the shaft. The shaft 747, Fig. 52, carries cams (see below) which are employed for timing the tape advance operation, and a shuttle cam 782 having a grooved track engaged by a camfollower 819 on the end of a pivoted lever 806. The other end of the lever is forked to engage a stud 812 on a plate 802 supported between rollers 797-800. Rotation of shaft 747 thus causes plate 802 to be reciprocated back and forth. One end of the plate extends over the recording tape and carries the recording head 712. The plate also carries the wiper of a commutator (not shown in Fig. 52) which is caused to traverse across a stationary assembly of contacts to connect potentials representing the code elements which are set up on the contacts to the recording head in sequence during its traverse. The tape is of a width sufficient to accommodate ten code elements, but for the present purpose is employed to record only five elements which form the standard telegraph code, the commutator being formed with five contacts. The operation is timed so that the recording takes place in the first part of the rotation of shaft 747. A further contact (not shown) is arranged to remain broken whilst plate 802 is away from its rest position and serves to lock the telegraph keyboard which supplies signals to the recording apparatus so that a further set of code element potentials cannot be set up on the commutator until the apparatus has completed a full cycle of operation. Tape advance mechanism, Fig. 50. The tape advance sprocket 702 is driven by a shaft 850 which is coupled to a drive motor (separate from that for shaft 747) via a friction clutch and which is normally held stationary by an escapement pawl 892 engaging a tooth of a ratchet wheel 852. At the completion of a rotation of the main shaft 747 (only the end section of which appears in Fig. 50) a cam 750 operates via a pivoted lever 906 to trip the escapement pawl and allow shaft 850 to be rotated clockwise through the distance of one tooth of the ratchet wheel. A new portion of the recording tape 708 is thereby drawn under the recording head ready for a subsequent traverse. The operation proceeds in this manner, step-by-step, during recording or reproduction, until notch 719, Fig. 40, in the tape is reached. This allows a switch S504, which has a bearer 945 sensing the edge 723 of the tape, to operate and close the circuit of a warning lamp. Operation may continue however until notch 718, Fig. 40, arrives. At this point the tape aligns with a part of sprocket 702 which is recessed between faces 947 and 948. The notch allows a sensing lever 932 to move inwardly towards the tape and operate a switch S503 and break the circuit of the electromagnet of the stop mechanism on the main shaft so that further operation of the apparatus is prevented. To rewind the recording tape, the direction of rotation of the motor for shaft 850 is reversed. As soon as the shaft commences to rotate, a disc 854 which is held between friction discs displaces a lever 916 and withdraws the escapement pawl from the ratchet wheel. This allows the rewind to take place rapidly with continuous rotation of shaft 850. The escapement pawl is locked in its displaced position by a trip mechanism 920. At the completion of rewind notch 720, Fig. 41, arrives and allows sensing lever 932 to move inwardly. The lever operates switch S503 again, which here does not enter into the operation, and also operates an associated switch S505 to signal that the rewind operation is complete. Additionally the tip 938 of the lever engages face 947 on the recessed part of sprocket 702 and positively stops further rotation. If now the motor for shaft 850 is reversed for a recording or reproduction operation, the shaft makes an initial movement until face 948 on sprocket 702 engages tip 938 of the sensing lever. The spacing between faces 947 and 948 is arranged to be such that the tape moves a distance greater than the spacing between the recording and erase heads. The movement is necessary during recording to ensure that the erase head clears the tape over the space between the two heads. When face 948 engages tip 938, the lever is forced downwardly (its pivot hole 934 being elongated to allow this) and engages an extension 928 on the trip mechanism 920 to release the escapement for normal operation. At the completion of the first rotation of main shaft 850, a cam 750 operates a pivoted lever 950 and moves the sensing lever out of engagement with face 948 on to sprocket 702 to allow the normal step-bystep movement to recommence. Specifications 854,084 and 854,085 also are referred to.