| 摘要 |
1,127,563. Automatic position control. INTERNATIONAL BUSINESS MACHINES CORP. Feb. 17, 1967 [ March 2, 1966], No. 7584/67. Addition to 987, 357. Heading G3R. [Also in Divisions G4 and G5] In a memory system according to the parent Specification in which a magnetic transducer is positioned over a desired data track by a servosystem actuated in response to servo-signals recorded in tracks adjacent the data tracks, the servo-signals in adjacent tracks are of the same frequency but have portions in anti-phase so that when the transducer is positioned over the desired data track no servo error signals are produced. As described, a disc 10 (Fig. 1) has magnetizable layers 11, 12 respectively of high and low coercivity and carrying respectively servo-tracks ST 1 -- Fig. 3 (not shown) and data tracks DT 1 -- spaced between the servo-tracks. The servo-tracks may, however, be arranged above or below the associated data tracks. The servo-signals (Fig. 4) are sinusoidal over most of their length but are reversed in phase at selected points such as 1 1 -1 3 , t 1 and 1 4 , t 2 so as to define periods a 1 , b 1 &c. of duration indicative of particular tracks by which coarse positioning of the transducer is achieved. The main leading and trailing phase reversals 1 2 , 1 4 and t 1 , t 2 are arranged on radial and spiral lines LR 1 - - - and LS 1 --- respectively. Servo-control: The servo-signal picked up by the head 21 (Fig. 1) takes the form of a suppressedcarrier, double-sideband signal which is separated from the data signals by a band pass amplifier 23 and smoothed by a filter 31 so that the resulting servo-signal has positive pulses at the radial lines and negative pulses at the spiral lines. The radial and spiral line pulses are separated at 32, 33 and fed to a coarse position detector 40 (also Fig. 2) to position the head near the addressed track. The positive (radial) pulses actuate an oscillator 46 to start a binary count cycle whose instantaneous value is compared with an address register 41 and a differentially timed pulse generated, when the values are equal, for comparison in phase discriminator 62 with a negative (spiral) pulse, the output of the discriminator controlling the head position actuator 64. A gate 61 is arranged to be opened when the coarse error signal from the detector 40 is minimal so that fine position signals, filtered from the amplifier 23 and demodulated 52, may pass to a summing gate 62 and thence to the actuator 64, control stability being improved by a tachometer. The demodulating carrier is derived from oscillator 46 in the detector 40 and the resulting, demodulated fine error signals are of amplitude and polarity indicative of magnitude and direction of error. |
