Patent GB-1310497-A (GB)
Title: Synchronizing system
IPC: G05F1/00
Filed: 1969-03-21
Abstract: 1310497 Automatic speed control R C A CORPORATION 12 June 1970 [21 March 1969] 14947/69 Heading G3R In a system for synchronising the reproduction of a video signal recorded on tape 2 with a reference signal, power is applied to capstan motor 4 and to headwheel motor 10 upon initiation of playback. A logic unit 64 senses lack of coincidence between the output of divider 44 and the inputs to circuits 40 and 58 whereby switch 36 transmits edit pulses on lead 34 to gate 52. The signal on lead 50 is compared with a reference signal, the resultant error signal on lead 80 causing the tape to be driven at a speed to cause phase coincidence between the divided control signal and reference frame. However, the output of divider 44 may not coincide with the transition of a frame on the tape. If the edit pulses on the tape are of the correct frequency and are phased correctly with respect to the video track containing the frame transition, the output of the divider at the beginning of a new cycle coincides with a frame transition whereby the video frames played back are synchronised with the frame occurrence as represented by the frequency of the reference generator 62. If the edit pulses on the tape are of incorrect frequency and locking to the wrong edit pulse takes place, the circuit 58 will indicate coincidence of the divider output with the reference frame of the generator 62. However, circuit 40 indicates non-coincidence between the divider output and the tape frame signal which is now available from circuit 16. Unit 64 enables circuit 68 and, at the end of one second, a signal is applied to logic unit 72. The output on lead 74 continues to indicate non-coincidence between tape frame and divider output so that the combination of inputs to the unit 72 provides an output signal on lead 76. Switch 36 couples the tape frame signal on lead 38 to the gate 52 to initiate a new divider cycle. The comparator 78 operates the capstan until coincidence occurs between the divider output and the reference frame signal of the generator 62. During this action, the circuit 58 applies a signal through the unit 64 to the switch 36 causing it to transmit edit pulses to the gate 52. The output of the divider 44 is now controlled by the desired one of the edit pulses whereby the playback is correctly synchronised with the reference frame. When there are no edit pulses recorded on the tape 2, the circuit 26 senses no coincidence between the edit pulse on lead 28 and the head identity signal on lead 24 so that there is no output on lead 34 to switch 36, and divider 44 is not controlled. If the output of the divider is wrong, its cycle is repeated and is then set to provide a signal corresponding with the correct one of eight possible timed outputs. The comparator 78 and capstan drive 4 operate the system for coincidence with the reference frame and the system remains properly synchronised in the absence of a disturbance. If a disturbance continues for more that a second, the sequence of setting the divider 44 and re-servoing the system takes place. Playback is not interrupted in the event of instantaneous disturbance. If incorrectly phased pulses are sensed, circuit 26 responds to prevent synchronisation until correctly phased edit pulses are present. When there are no edit pulses on the tape, and the frame signals are unreliable and continue to be so for more than one second, they are prevented from controlling synchronisation of the system.