Patent GB-801639-A (GB)
Title: Automatic synchronization apparatus for long-time transverse magnetic sound recording and reproducer
Inventor: HENRYLYON WILLIAM
IPC: G11B5/02
Filed: 1956-05-03
Abstract: 801,639. Magnetic recording and reproducing apparatus. SOUNDSCRIBER CORPORATION. May 3, 1956, No. 13724/56. Class 40 (2). In a magnetic record apparatus of the kind described in Specification 797,619 the spaced arcuate tracks are synchronized with the path followed by the heads by means actuated by the movement of the tape to periodically lock the tape feed roller against rotation, and means responsive to the movement of the heads to the edge of the tape to release the feed roller again. In the embodiment described the tape is provided with equidistant holes 24a along its length through which an electrical brush contact 51 trips an electronic device to operate a magnetic brake 23 and stop rotation of the tape feed roller shaft 39 until a particular one of four cams 13 associated with the transducer 12 at that moment passing from the tape momentarily closes a pair of contacts 14, 16 to trigger the release of the magnetic brake 23 to restore the drive of the tape. The feed roller is driven by gears 41a and 41, the latter gear being frictionally coupled to the feed roller shaft 39 so that it slips when the brake 23 is applied. Fig. 4 illustrates in exaggerated form the principle of the device. In section 95, the first full line 52 represents both a first recorded track and the path of a reproducing head. The second, third and fourth full lines 52 represent the recorded tracks in successive advancement of the path 97, shown dotted, of the reproducing heads. When the tape advancement is arrested the transducer follows a truly arcuate path on the tape as indicated by the double dotted line 98, 99, and comes into synchronization with the recorded track at point 96 and follows it to the point 100 at the edge of the tape, at. which point the tape drive is restored. The recorded track from point 96 to 100 also follows a truly arcuate path because the travel of the tape would have been similarly arrested during recording. In the event of the transducer paths tending to lag behind the recorded track as shown in Section 101, the transducer path does not coincide with the recorded trace until a point 105 near the edge of the tape is reached, thus the braking period is reduced accordingly. Details are given of the electronic control device which comprises a valve whose emission is increased by a positive bias when contact is made through hole 24a whereby a charged condenser is made to operate a relay to close the circuit of the magnetic brake. An eccentric roller 31 is provided whereby optimum position of the transducer relative to the tracks is obtained. In practice the deviation between the heads and tracks prior to synchronizing pulses is insufficient to cause deterioration of reproduction owing to the appreciable width of the tracks, and the function of the device is to prevent a deviation which produces an unacceptable deterioration. The invention is not limited to the use of a hole in the tape. A conductive mark or line passing under two brushes could be employed.