Patent GB-655373-A (GB)
Title: Improvements in or relating to methods of, and apparatus for, producing magnetic recordings
IPC: G11B15/43
Filed: 1947-12-31
Abstract: 655,373. Automatic speed control systems. BRUSH DEVELOPMENT CO. Dec. 31,1947, No. 35218. Convention date, Jan. 4. [Class 38 (iv)] [Also in Group XXXVIII] Copies of a magnetic recording are produced by transducing the signals from a master record in reverse sequence and storing the copy record member in coiled form so that it is ready for subsequent reproduction of the copied signal in correct sequence. In Fig. 1 a master recording tape 31 is fed from supply reel 41 via magnetic transducing head 48 to take-up reel 42. The output from head 48 is supplied to amplifier 60, which has a plurality of output terminals, each pair of which is connected to a magnetic recording head 75. The heads 75 are located along separate channels along a wide magnetic copy track 71 to produce a plurality of copy recordings, which after cutting by blades 82 are wound on individual reels 90. A second transducer head 47 is associated with tape 31 which may be used for erasing purposes, when, for example the head 48 is adapted for recording on the tape 31. Pads 49 keep tape 31 in contact with heads 47, 48. Tape 31 is driven by roller 52 which is rotated at a constant speed, loops 31-1 and 31-2 being provided to absorb speed differences which may occur between the speed of roller 52 and that of the driven reels 41, 42. Tape 71 is driven by roller 82. Various means of fixing the separate record tapes to different types of reels 90, are described (Figs. 3, 4, 5, not shown), or a single reel taking the whole width of tape and afterwards cut into sections may be used. Figs. 6 and 9 show a modification of the means for feeding tape 31 which includes means for maintaining the length of loops 31-1, 31-2 constant, and a second tape 32 with associated supply reel 111 and take-up reel 113 is fixed behind the tape 31 and reels 110, 112. When tape 31 is being used for reproduction, it is held against transducer 148 by a roller 170 on arm 160 and which engages roller 152 which is driven at a constant speed. The opposite arm 161 and roller 171 are held free of tape 32 during this process so that tape 32 is then rewound without being in contact with its associated transducer head 149. When arms 160, 161 are rotated, tape 31 rewinds free of contact from transducer 148 while tape 32 is held in contact with transducer 149. The recordings on tapes 31, 32 are in opposite directions, so that when the direction of winding as changed and a different tape utilized, reproduction may continue in the same sense as before. Each master record is reproduced in reverse so that the copies need not be rewound. Pads 49 are attached to levers 185 which are engaged by pins on arms 160, 161, so that the tape concerned is held against the appropriate transducer head. The drive and lever mechanism may be arranged independently, so that a recording of two submaster records may be carried out in one operation, for subsequent use as the two master records for duplicating purposes. The reels 110, 111, 112, 113, are rotated by motors, such that with no resistance in series with the motor, they rotate at a slightly higher speed than the rollers 152, 153. Loops 31-1, 31-2, around floating rollers 35, 36, hang freely, and a light beam is provided across each of the paths of rollers 35, 36 to energize photoelectric cells 292. The outputs from cells 292 are used to.control relays 280 which may shortcircuit resistances 185, 186 which are connected in circuit with the motors driving reels 110, 111 and 112, 113. The arrangement is such that resistance 185 is short-circuited unless reel 35 intercepts the light beam, and resistance 186 is short-circuited only when reel 36 intercepts the light beam, so that during operation, reels 35, 36 maintain a substantially constant position about the level of the light beam. Alternative means such as lever controlled switches may be used in place of the photoelectric cell arrangement, and a time-lag means such as a dash-pot may be introduced. Resistances 185, 186, may also be made variable and controlled by a servo mechanism, to compensate for the change in diameter of the reel of tape. A further arrangement is described (Fig. 10, not shown), in which loops 31-1, 31-2 are omitted, and the tape is secured to the supply and take-up reels via a resilient spring mounting. The tapes may also be guided along two fixed paths each with an associated transducer, the arrangement then being such that the transducer and intermediate impeller means for each tape are deenergized during the recording operation for that tape. The tapes may have special characteristics, such as a conducting portion, which may be used to automatically control the reversal operation, to indicate the end of the recording, or for other purposes. As an alternative to the use of two master records an endless band may be used for continuous reproduction.