Patent GB-883637-A (GB)
Title: Improvements in tape transducing apparatus
IPC: H04N5/782
Filed: 1959-03-03
Abstract: 883,637. Automatic control systems for tape transducers. AMPEX CORPORATION. March 3, 1959 [March 10, 1958], No. 7431/59. Class 38 (4). [Also in Group XXXVIII] In tape transducing apparatus in which signals are recorded on successive tracks, extending transversely across the tape, produced by a rotary type transducing head, timing errors in the reproduced signals are eliminated by automatic control of the pressure between tape and head. In Fig. 1 magnetic recording tape 11 is fed by a capstan 13 past a rotating drum 18 carrying four television signal recording heads 16 which sweep the tape transversely. The tape is cupped around drum 18 by a guide 21 which is movable manually and automatically relative to the drum to vary the pressure applied to the tape. Recording.-During- recording, a motor 19 supplied through a frequency multiplier 37 from a mains or oscillator A.C. source 36 drives the drum 18. Amplified signals derived from a photo-electric square-wave generator 39 driven by motor 19 are supplied to a motor 48 driving capstan 13 so that the head and capstan motors are maintained in a fixed speed ratio. The four head windings 1-4 are supplied through an amplifier 63 with video signals which are frequency modulated at 62. Sound is recorded on one edge of the tape by a head 32 and a control signal derived from photo-electric generator 39 is recorded on the other edge of the tape by a head 31. Erase heads 33 and 34 are provided ahead of the control signal and sound heads respectively. Playback.-During playback heads 1-4 are connected in sequence by an electronic switch 61 triggered by pulses derived from photoelectric generator 39, and the reproduced output is supplied through a demodulator 76 and amplifier 77. Capstan motor 48 is supplied from a separate oscillator 52 the frequency of which is automatically controlled through a reactance valve to maintain phase synchronism between pulses derived from photo-electric generator 39 and the control pulses recorded on the tape. Motor 19 driving the heads is still supplied from A.C. source 36 but any variation from the average interval between synchronising pulses, of the interval between the two horizontal synchronising pulses from playback amplifier 77 which occur immediately before and immediately after switching from one head to the next is detected electronically in a unit 78 which then effects correction by control of a follow-up servomotor 85 adjusting the position of guide 21 relative to the tape. If during playback the picture becomes degraded a relay 79 responsive to the signals from playback amplifier 77 changes control of motor 85 from automatic to manual. Control of the tape .guide.-Tape guide 21, Fig. 7, is attached to a lever 157 pivoted on a base plate 130 so that the guide is urged towards heads 16. on rotating drum 18 by a compression spring 152 acting through a roller 154 engaging an inclined surface 156. The curved surface of the guide may be provided with recesses associated with a source of suction to maintain the tape in intimate contact with the guide surface. Servomotor 85 (not shown in Fig. 7) automatically controls the position of the tape guide by adjusting the vertical position of a cone 201 through gearing 197, 198 so that through a lever 166, an adjustable member 164, and a cam 161, lever 157 is moved in opposition to spring 152. Cam 161 may be operated by de-energization of a rotary solenoid 167 to move the tape guide sufficiently to release the tape for re-winding. Pneumatic cooling and dust extraction is provided for the head assembly. The pressure applied by tape guide 21 may alternatively be controlled by controlling the suction between guide and tape. Specifications 798,927, 798,928, 798,929 and 798,930 are referred to.