Patent GB-1231941-A (GB)
IPC: H04N5/781
Filed: 1969-03-14
Abstract: 1,231,941. Recording television signals, AMPEX CORP. 14 March, 1969 [18 March, 1968], No. 13591/69. Heading H4F. [Also in Divisions G4-G6] Specification describes a video disc recorder whereby, by omitting or repeating fields in the playback process various fast or slow motion effects may be produced. Mechanics. Figs. 1, 2, 3, 4, 6, 8, 9.-The recording medium comprises two double sided records 11 and 12 and four magnetic recording/ erase/playback heads 16, 17, 18 and 19 cooperating with the upper and lower faces of record 11 and the upper and lower faces of record 12 respectively and radially carried on carriages 21 on respective arms 22. The carriage and head is moved in a stepped fashion by means of belt 37 turned by stepping motor 23. Each face is allotted eight tracks each occupying one revolution at 60 r.p.s. Reversal of the movement of the carriage at the end of its range of movement l is caused by a projection 58 (Fig. 6) interrupting the light from source 54 to photo-cells 57. Early interruption of the light on photo-cells 69a and 69b, slows down and prepares the carriage for said reversal. The position of the photo-cells and thus length l is adjusted by means of lead screws 62. Overshoot of the carriage actuates a microswitch 41 and shuts off the motor 23. The head 19 is urged against the record face by springs 94 and 107 and is provided with means adjusting its attitude in pitch and yaw. Recording format, Fig. 11.-Fig. 11 shows the position and function of each head over a period of thirty-eight fields, each head undergoing a four field cycle of erase (E), record (R), movement (M) and movement (M)-i.e. E.R.M.M. Thus field 1, is recorded on the outer or track 1 of the top face of record 11, by means of head 16. Head 17 is meanwhile erasing track 1 on the underface of the record. Field 2 is then recorded on this erased track, head 16 moving to the second track on the top face and track 1 on the top face of record 12 being erased preparatory to the recording thereon of field 3. During said recording of field 3, head 16 moves to track 3 and head 17 moves to track 2. During field 14, head 16 moves to the inner or track 8. This causes obstruction of the photocells 69b midway between track 7 and track 8 (ss) whereby the head remains in track 8 for field 15, 16 and 17, recording the latter, and then commences to return to the outer track using the same E.R.M.M. format. Thus odd number tracks are recorded on during the inwards movement of the heads and the remaining even num - ber tracks are recorded on during the outwards movement of the heads. Thus after thirty-two fields the recorded contents of the four faces may be tabulated thus. During field 30 the outer photo-cell 69a is obstructed and the head 16 returns to its inward movement to start the recording of a new set of thirty-two fields. Recording electronics. Figs. 10A, 10B, 10C, 10D, 11, 12A, 12B.-To commence recording, switch 52 of control means 127 is closed, giving Q1 = 0 and from 128, P 2  =, P 4  = 1. The latter condition operates gate assembly 130 whereby the staggered recording gate pulses EAC, EBC, ECC, EDC, Fig. 12B are applied to respective head amplifiers 126a-126d. Each amplifier is thus gated to record according to the format E.R.M.M. The recording gate pulses also control the application of a D.C. erase voltage to the heads. The various pulses involved are produced from the line and field sync. pulses COMP. SYNC, Fig. 12A incident at sync. separator 121 as follows: Separator produces a pulse T embracing the equalizing pulses and the vertical sync. pulse. During the record mode pulses T are passed by logic circuit 131 as pulses T s  to clock generator 132. Generator 132 produces pulses G and C respectively defining the ends and the beginnings of successive fields. Pulses G also cause 132 to produce rectangular pulses Be (D G  during record mode). Pulses C are fed to slow motion logic 133 to produce pulses the ends and the beginnings of successive fields. Pulses G also cause 132 to produce rectangular pulses B c  (D G  during record mode). Pulses C are fed to slow motion logic 133 to produce pulses J c  during said record mode. Pulses D G , Fig. 12B, produce pulses L in head logic 134. Signals E AG , E BG , E CG , E DG  are produced by logic 134 by combination of pulses L and G. (Pulses synchronous with the pulses G will have a second suffix G and those synchronous with the pulses C the second suffix C). Signals E AG  and E CG  are fed via logic circuits 137 and 138 (wherein they become E AK  and E CK ) to retiming logic circuit 136 where they are resynchronized with the pulses C to become E AC  and E GC - Signals E BG  and E DG  are fed directly to logic circuit 136 to become E BC  and E DC . Carriages logic circuit 137 produces carriage movement control (i.e. motor 23 control) pulses F AG , F BG , F CG , F DG - These pulses are resynohronized in logic circuits 139 and 141 to become motor stepping pulses F AC , F BC , F CC , F DC . The signal Q applied to logic circuit 141 inhibits the stepping pulses when the records are turning. Depending on whether the stepping movement of the carriages (heads) is inwards or outwards, pulses FAC0, FAC1 &c., are fed to the stepping motors from logic circuit 142. In the case of head 16, obstruction of the photo-cell 51a produces a signal Y A  which inhibits, in logic circuit 143, the production of the eight stepping pulse FAC0 during field 31. Signal R D , produced in logic circuit 122 from the frame sync. derived pulse S R , is used to synchronize the servo controlled rotation of the records. Replay. Speed normal-forward. (Left-hand side, Fig. 13).-Switch S9 of means 144 and switch S 5  of means 127 are closed giving P 1=1  and P 4=0  (from logic circuit 128). The head gating signals E AC , E BC , E cc , E DC , are passed by reproduction gates 130 to open heads 16, 17, 18, 19 in sequence as before. No erasure signals are introduced. The replay video signal, frequency modulated on a carrier, is detected by demodulator 147. Via switch 148 (not activated in the normal mode), the video signal passes to a horizontal sync. convector AMTEC, 150a wherein the phase of the video is adjusted relative to a horizontal drive signal from reference delay 151b. In the case of a colour signal the phase of the chrominance sub-carrier may be inverted on alternate fields in means 151 and corrected with reference to an external 3À5 mc/s. signal, in COLORTEC means 151a. The horizontal drive signal is derived from a signal S y  produced by the sync. separator 121. So that the AMTEC means 150a operates in the middle of its range of control, the phase error output of the AMTEC is passed to means 122 to readjust the phase control signal R D  of the record drive. The output of the COLORTEC means 151a is fed to processor and/or utilizer means. Speed normal-reverse. (Middle of Fig. 13).- Switch S3 of means 127 is closed, whereby Q 2=1  and P 2  changes from 1 to 0 from 128. P 2  is fed to means 131, and, if not in the " fast search " mode of operation, reappears therefrom as signal P 25 =   0  which is fed to means 138 When signal E BG  first goes to zero after the initiation of the reverse mode, means 138 is rendered operative and the next pulse is signal E BG  produces a signal K which causes signals E AG  and E CG  output of circuit 138 and E AG  from output E CK  The carriage movement control signals F AG  and F CG  are likewise interchanged at outputs F CK  (F AG ) and F AK  (F CG ). Pulse N also generated by circuit 138 is fed to circuit 143 to change signal M therefrom from 0 to 1 whereby the carriages commence to move outwards. In an analysis of Fig. 13 it is seen that in forward replay the gate signals fed to head 16 are in advance of those fed to head 17 which are in advance of those fed to head 18, &c. but in reverse replay, the mirror image of these gate signals applies, i.e. the gate signals of head 16 lag those of gate 17 &c. The same change is observed for the stepping signals of the carriage motors. To change back to forward replay, switch S5 is closed: P 2  goes to 0 and the system reverts to the forward mode after the next first pulse in signal E BG  In the reverse mode, the phase of the chrominance sub-carrier is no longer coherent from field to field, i.e. consecutive carriers are 180 degrees out of phase. Chrominance inverter 151 thus inverts every other field under control of circuit 152 and alternate field switch 153. Slow motion (Fig. 14).-Switch S5 (127) is closed together with any one of switches S6/S8 depending on the required speed. Under the control of signals Q 6 , Q 7  and Q 8  produced by means 144, oscillation 154 produces a square wave A 1  having a frequency F A  according to the table:- From square wave A 1  logic circuit 128 produces a corresponding signal A, Fig. 14, which is fed to circuit 156. If the system is not in the alternate field mode, signal A is fed as its complement to time quantizer 157. In quantizer 157 to sync. signal G, Fig. 12A, is used to time quantize the signal A A , i.e. signal A A  is converted to signal Z 1  wherein each pulse in A A  is converted to one in Z 1  commencing at the start of the A A  pulse and ending at the start of the next G pulse. When starts are coincident, the start of the pulse in Z 1  is delayed (see dotted outline) to miss the pulse in G. The trailing edges of the Z 1  pulses switch on a bi-stable to give Z G  and D G , wherein marks and spaces are multiples of field length and are separated out by circuits 134, 137, 138 and 136 into head gating signals E AC , E BC , E CC , E DC  Slow motion replay is thus produced, e.g. by repeating the read of the field 9 three times and the field 10 twice &c. It will thus be seen that it takes twenty-one field periods to rerpoduce nine (n) fields whereby the motion is reduced by 9/ 21  or <SP>3</SP>/ 7 . Two successive replays of the same field however will not be interlaced and a