| 摘要 |
1,260,706. Automatic control of position. INTERNATIONAL BUSINESS MACHINES CORP. April 28, 1969 [April 29, 1968], No.21527/69. Heading G3R. [Also in Division G5] A support carrying a row of data transducers 24 has also two servo transducers 26, 28 cooperating with servo tracks 12, 14 recorded on a medium 18 to produce a control signal for positioning the support so that a particular one of the data transducers is correctly disposed in relation to a particular one of several data tracks. The transducer may be magnetic or photo-electric and the medium may be drum, disc or tape. Initial track selection is made by an undisclosed coarse position control 34 and the invention maintains the position of the transducers in relation to the selected tracks. Two servo transducers are used at opposite ends of the support bar to compensate for changes in its length due to temperature and humidity, and their outputs are connected to the ends of a voltage divider 36 whose individual resistance values correspond to the spacing of the data heads. By selecting the appropriate tapping point, e.g. 50, by a switch 44 the respective servo transducer outputs are "weighted" so that the selected data transducer, e.g. 48, is accurately aligned with its track. To correct for spacing errors in manufacture a further, fixed, bias may be applied from a resistance bridge network 60 or from a printed circuit board Fig.2 (not shown) in which resistors are inserted or links removed. The servo tracks are recorded with square waves, all of the same frequency, adjacent tracks being phase displaced by 90 degrees, and periodically there is a synchronizing pulse, in phase on all servo tracks, at which point the square wave is phase displaced 180 degrees on each track Fig. 3 (not shown). This arrangement is to eliminate the effect of low frequency noise which may pass filters 30, which are connected to comparison circuits 32, the outputs of which are zero when its associated transducer is aligned between two servo tracks. The comparison circuits Fig. 5 (not shown) each comprise a flip-flop controlled by an oscillator at the square wave frequency (and synchronized therewith by the synchronized pulses) which gates alternate pulses from the transducer to separate peak detector circuits. Hence, these detect the level of the signals from respective tracks on either side of the transducer, any difference between them (because the transducer is nearer to one track than the other) producing a control signal. Noise produces a bias which changes polarity after each sync pulse so that the average effect of this is zero. |
