Patent GB-1511509-A (GB)
Title: Magnetic recording apparatus
IPC: H04N5/7826
Filed: 1975-07-10
Abstract: 1511509 Video magnetic tape recorder H TANIMURA 10 July 1975 [17 July 1974] 29066/75 Heading G5R In a video magnetic tape recorder desired video fields from a continuous video signal are extracted and recorded by one rotary head 5, Fig. 1, on a longitudinal track on a tape around a rotary head drum 3 while the tape is stationary the tape is stepped around the drum 3 by an intermittent tape drive controlled by means 36 having an input coupled to means 13 detecting the rotational phase of rotary video heads 5, 6 and an input coupled to a pulse generator 46 responsive to the video playback signal from head 6 for generating a pulse at the instant the video playback signal ceases, and a head rotating motor 11 has a control means 40 supplying a phase error signal thereto and having inputs from pulse generator 46 and from the rotational phase detector 13. In apparatus using two rotary heads 5, 6, only head 5 is used for recording the longitudinal video track with selected video fields from input 55 and FM modulator 42a under the control of a gate 42b, head 5 effecting recording between points I and II, Fig. 3, on drum 3. Gate 42b is controlled by a gating signal generator 43 having a manually applied record command input 58 and an input 74 from a ¢ frequency divider 50 which gives an output pulse at 73 at ¢ the vertical synchronous pulse rate, produced by processing outputs 66, 67 of a field discriminating circuit 53, output 67 being the vertical synchronous signal of the video input and output 66 giving a pulse for each odd field but no pulses for even fields. The speed of heads 5, 6 is controlled during such recording of a first field on a blank tape by control of motor 11 by a phase comparator 40 comparing in phase a first signal from a ramp wave generator 41, controlled by the output 73 of divider 50, and a second signal induced in stationary head 13 by a magnet 14 rotating with heads 5, 6 and passed to comparator 40 via delay 35, gate 48 and switch 47. After recording of each field the tape is advanced in response to a command manually applied at input 82 of plunger drive circuit 36 whereby plungers 17, 27 are energized to release tape clamps 15a, 16a, 15b, 16b and engage pinch roller 29 with capstan 28 to drive the tape for a period controlled by inputs to circuit 36 from head 13 and from the pulse generator 46 responding to playback by head 6 of the field just recorded. The tape is stopped so that the end of the last field is at point I on drum 3 whereby successive fields are in contiguous track portions. Due to mechanical play stoppage may not occur exactly at point I but the circuitry is arranged to control the recording position on drum 3 to maintain the track portions contiguous. During recording of the second, third &c. selected fields the inputs to the motor-controlling comparator 40 are from generator 41 and, via switch 47 and gate 48, from pulse generator 46 responding to replay by head 6 of the part of the previous field site on drum 3. A recording command input to terminal 59 of switch 47 causes the second input to comparator 40 to be supplied from divider 50 via shaping circuit 52 for a period after recording of each of the second and subsequent selected fields until circuit 51 determines that the outputs of shaper 52 and generator 46 are in phase whereupon the second input of comparator 40 is switched back to generator 46. The above method records only even fields and in order to maintain consistent horizontal synchronous signal phase at the juncture between recorded fields the heads 5, 6 are not exactly 180 degrees apart but are spaced so that the two angles between them, #A, #B are given by #A/#5=α, #B/#5=#; α+#=525, #5=360/525 (for 525 line systems); thus if #A/#B=262/263 adjacent fields have overlapped portions, or blank portions therebetween, corresponding to ¢ H, H being the horizontal synchronous period. Alternatively, with 180 degree head spacing, the two outputs 72, 73 of divider 50 representing even and odd fields respectively may be used so that even and odd fields are recorded alternately, or recording is controlled to last for periods of MH, M being an integer, and only even or only odd fields are recorded. During PLAYBACK both heads 5, 6 are used to repeatedly scan a field on the stationary tape giving an output at 56 via rotary transformer 9, 10, amplifier 44, 45, mixer 49 and demodulator 54. Substitution of a given recorded field by a new field can be effected by controlling the tape drive to position the required tape portion on the drum 3 while watching the playback output at 56 on a monitor. For this purpose, a tape feed circuit 38 controlling plungers 17, 27 has a start drive command manually applied at input 57a and stops tape drive in response to a manually applied input at terminal 57b, an input from stationary head 13 via delays 35, 37, and a vertical synchronous signal provided from the playback signal by synchronous separator 39. Head 5 may receive an erase signal to erase the old field prior to recording the new one, or may just record over the old field. Alternative embodiments may have three, four or more rotary heads. In a three head arrangement, Fig. 14 (not shown) the tape is wrapped at least 2/3 around the head drum, one head is used for recording and all three for playback and the tape may be in motion during playback.