Patent GB-665179-A (GB)
Title: Data recording and reproducing apparatus
IPC: G11B5/00
Filed: 1949-05-24
Abstract: 665,179. Statistical apparatus. ECKERTMAUCHLY COMPUTER CORPORATION. May 24, 1949 [May 27, 1948], No. 13885/49. Class 106 (i). Data recording and reproducing apparatus includes a pick-up device responsive to code pulses carried by a code pulse-bearing member, means for moving the member past the pick-up device to bring successive pulses adjacent the pick-up device, and means to produce in the pick-up device an alternating signal from each code pulse. The apparatus described employs magnetic tape for storing coded information in the form of minute magnetized spots, referred to as "pulses," arranged in a plurality of channels lengthwise of the tape. Particular combinations of pulses at corresponding sections may represent numerical or alphabetical data, machine instructions, &c., In order to obtain satisfactory reproduction at very slow tape speeds, a rapid vibration (e.g. 400 c/s.) of small amplitude is imparted to the tape 344, Fig. 8, in the vicinity of a rigidlymounted pick-up H by a loud-speaker type of driving device 384. In this way an output signal is obtained involving a modulated carrier having the frequency of the vibration, the modulations depending upon the pulses in the tape. Thus the output may be used to drive directly, without intermediate memory devices, typewriters or other printing or punching apparatus. Only the small loop of tape below idlers 362, 364 supported by spring-members 376, 378 fixed to a block 374, is subject to vibration. The tape is fed by a wheel 358, faced with friction material, driven through a worm 370 and worm-wheel 368 by a motor 372. A tape supply reel 352 and take-up reel 356 are energized by motors 350, 354, respectively, to take up slack in the tape. The recording and reproducing heads.comprise stacks of accurately dimensioned laminations 338, 340, Fig. 7, carrying windings 342 and located in milled slots 320, 322, Fig. 3, in blocks 302, 304, 306, of non-magnetic material such as beryllium-copper. Shims 334, 336 interrupt the continuity of the laminated cores and define gaps which are required for both producing magnetization of the tape and for reading out the signals therefrom. Eight heads are provided in two groups, staggered to align with eight channels in the tape which is guided by discs 316, 318. To prevent cross-talk between adjacent heads, thin soft iron shims 328 are inserted between the heads. Amplifier and phase detector. One of these units A, Fig. 1A, is associated with each recording and reproducing head. Signals picked up by the coil 2 of the head are applied across the primary of a transformer 12, the secondary of which is tuned by a condenser 14 to the standard frequency of the system (e.g. 400 c/s.). The signals pass through a condenser 16 to the control grid of a pentode 18 and the output from the anode of this valve passes through, a condenser 34 to the control grid of a second pentode 36. The anode of this valve is connected through a condenser 51 to the grid of a triode 52 in a cathode-follower circuit which provides negative feed-back to the pentode 18 to ensure uniform gain, and delivers amplified signals through a condenser 62 to the grid of a triode 64 so arranged that the positive peaks of the signals drive the valve well into saturation while the negative peaks drive it beyond cut-off. Thus the sinusoidal signal is transformed into a series of narrow pulses, a positive swing of the control grid of the pentode 18 producing a negative pulse at the anode of the triode 64. These negative pulses are fed to a diode gating circuit providing phase detection. The signal generator D, Fig. 1A, comprises a Colpitts oscillator 106 giving an output at the standard frequency which is fed through a blocking condenser 124 to the grid of a phase inverter 126 having two cathode resistors 130, 132 with a total series resistance approximately equal to the anode resistor 134 across which signals approximately equal in magnitude but of opposite phase are developed and fed to power amplifiers 140, 142 connected in pushpull to an output transformer 150, the secondary of which is matched with and connected to the tape oscillating driver 384 (Fig. 8) at terminals 153, 155. Terminal 153 is also connected by a line 157 to an adjustable phase-shifting device 156, 158 which compensates for any phase-shift which may occur in the electromechanical device which oscillates the tape. The signals pass through a condenser 160 and resistor 162 to a flip-flop 154 of a type suitable for low-speed operation. The outputs of the flip-flop, consisting of square waves 180 degrees out-of-phase with each other, are delivered to condensers 164, 166 which are connected with resistors 168, 170, respectively, to perform differentiation upon the square-wave signals. A pair of triodes 176, 178 are each biased to cut-off, and accordingly only the positive pulses which reach their respective grids 180 degrees out-of-phase with each other produce corresponding negative pulses across their resistors 180, 182. The potential to which the anodes may rise is limited by crystal diodes 184, 186. Negative pulses from a 10-volt origin are thus delivered to lines 84, 86. A phase-selective system responsive to the data signals, is provided by crystal diodes 72, 74, 80, 82 interconnecting the anode circuits of the triodes 64 (units A), 176 and 178 (unit D). When no pulses are provided at the anodes of the diodes 72, 82, for example, or when a negative pulse is applied to one and not to the other, the anodes remain positive and accordingly no output occurs through lines 104, 102. However, coincidence of negative pulses delivered to the diodes 72, 82 removes both sources of positive potential from their anodes and causes negative pulses to be transmitted through the diodes 96 to the line 104, and through diodes 98 and 100 to line 102. Diodes 74, 80 function in a similar manner to control the delivery of negative pulses to the line 92. Thus an "in-phase " condition of the control grid of the pentode 18 and the terminal 153 produces negative pulses in the line 92 and an " out-of-phase " condition produces negative pulses in.lines 102 and 104. When a pulse on the magnetic tape is first encountered by a head 2, its leading edge produces a signal at the grid of the pentode 18 which is 180 degrees out-of-phase with the output at the terminal 153. Negative pulses are transmitted through the line 102 to the grid of a conducting triode 204, Fig. 1B, in a flip. flop circuit 200, reversing the flip-flop and extinguishing a neon bulb 216. This causes a positive pulse to be emitted through a condenser 218, and the differentiating action provided by this condenser and a resistor 220 delivers a sharp positive pulse to the control grid of a normally non-conducting triode 224 causing a negative pulse from its anode to pass along a line 228. The trailing edge of a pulse on the tape produces a signal at the grid of the pentode 18, Fig. 1a, in phase with the output at the terminal 153. In this case a negative pulse through the line 92 restores the flip-flop 200, Fig. 1b. and the neon bulb 216, and a negative pulse from the flip-flop transmitted through the condenser 218 will have no effect on the triode 224. Passing through a condenser 232, however, and subject to the differentiating action of this condenser and a resistor 236, a sharp negative pulse will appear on the grid of a normally conducting triode 234, cutting it off momentarily. Meanwhile a negative pulse through the line 104 (see above) passing to a unit B (associated with each recording and reproducing head) is applied, through a switch 242, to the grid of a normally conducting triode 249 in a flip-flop circuit 244, reversing the flip-flop. This causes a neon bulb 246 to fire and a positive pulse from the anode of the tride 249 passes to the cathode of a crystal diode 258. If this coincides with a positive pulse from the anode of the triode 234 through the line 240 and crystal diode 256, the potential on the control grid of a pentode 260 is raised sufficiently to cause that valve to pass a large current which may be used for energization of a solenoid, e.g. for typewriter clutch mechanism &c. Instead of oscillating the tape the reluctance of the magnetic circuits may be varied. Also wire, punched tape, or photographic film with photo-electric pick-up means may be employed.