Patent GB-1201477-A (GB)
Title: Rotation control device
IPC: H02P29/00
Filed: 1967-11-06
Abstract: 1,201,477. Automatic speed control. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. Nov.6, 1967 [Nov.17, 1966], No.50394/67. Heading G3R. [Also in Divisions F2 and G5] In an apparatus for magnetically recording and reproducing a video signal, a rotary recording and reproducing head drum 53 is driven by a constant speed A.C. synchronous motor 70 through a continuously variable ratio friction gear comprising an elastic belt 75 embracing driving and driven pulleys, such as 76, 78 at least one of which is a conical pulley; the ratio of the gear is varied by braking the driven pulley at 79 so as to effect belt shift; and the brake 79, of the eddy-current type, is responsive to an error  signal representing the phase difference between the phase of rotation of the head drum 53 (detected, e.g. photo-electrically or magnetically) and the phase of a reference signal. Magnetic tape 57 is taken from a supply reel 58, past an idler 59 and a guide post 60, over a semi-cylindrical guide 52, past a guide post 61, a stationary control signal recording-reproducing head 62, a capstan 63 and an idler 64, and taken up on a take-up reel 65. The rotary head drum 53 has two magnetic heads 54, 55 which protrude through a slit in the guide 52. The arrangement is such that the tape runs helically over the guide 52 with the result that magnetized tracks 67, 68 of the form shown in Fig.1 are formed on the tape by the rotary heads 54, 55 whereas a continuous control signal track 69 is formed by the stationary head 62. In addition to the driving pulley 76, the motor 70 drives a capstan flywheel 72 through an elastic belt 73. Operation: In the recording mode, on one hand a composite video signal from a television receiver or camera is fed into a separator 91 where a vertical synchronizing pulse signal of 60 c.p.s. is solely separated and fed into a divider 92 a 30 c.p.s. pulse signal from which is then delayed and phase shifted at 93. On the other hand, a signal is derived from a pick-up head 102 adjacent a permanent magnet 101 on the rotary head drum 53. The signal at 93, taken through a switch S 1 , and the signal from the rotary head 53 are fed to a phase comparator 94, the error signal from which is smoothed by a low-pass filter 95 and amplified at 96 to provide an amplified D.C. output for supply to the brake 79. Meanwhile, the composite video signal is modulated (e.g. by an FM modulator) and passed through a recording amplifier to the rotary heads 54, 55, and, at the same time, the 30 c.p.s. pulse signal from 92 is fed through a switch S 2  and an amplifier 97 to the control head 62 to record a control signal track 69. The delay time of the phase shifter 93 is selected so that the periods of engage - ment and disengagement of the rotary heads 54, 55 lie in the television signal vertical blanking period. In the playback mode, the signal from the rotary head drum is compared at 94 with the control signal 69, recorded on the tape and fed through the amplifier 97, the switch S 2 , a phase shifter 99 and the switch S 1 . The delay time of the phase shifter 99 is so adjusted that the heads 54, 55 exactly trace the recorded tracks 67, 68.