GB847938A - Improvements in electrical control systems - Google Patents

Abstract

847,938. Electric correspondence control systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 21, 1956 [Dec. 28, 1955], No. 39121/56. Class 40(1). A transducer head is positioned adjacent the surface of a record medium in response to a signal derived between a tapping which moves along a current carrying strip and a tapping positioned on the strip at a point defining the required position of the transducer head, whereby the latter is brought to its required position by controlling it to bring the said signal to zero. As shown, Fig. 4, in a track selecting arrangement the strip PT made of conductive plastic material has potentials - A, +A applied across its ends and has end connections and tappings 10 to 90. Any strip length, e.g. that between tappings 50 and 60 may be selected by closing appropriate switches S, the tappings being thus extended to leads L, M, across which a further tapped resistance P1 . . . P10 is connected, the switch arm B being capable of being set to any tapping so as, in effect, to sub-divide the length between tappings 50, 60. The difference of potential between the arm B and the slider SL, attached to the transducer, operates through push-pull stages V4, V5 and V6, V7 to control clutches CL1, CL2 which cause the transducer together with the slider to move in a direction such as to reduce the difference of potential to zero. To reduce hunting the valves V6, V7 are further controlled by a differentiating circuit comprising capacitors C1, C2, C3 and valves V1, V2, V3. An embodiment is also described, Fig. 2 (not shown), including a further set of switches for further decimal subdivision. In an embodiment for locating a disc, Fig. 3, tappings on the strip PT are provided corresponding to each disc loaction. Thus the pair of reproducing heads T1, T2 is first put into the position of a record Rc and a probe PR moved along the strip until a voltmeter V records no voltage between the probe and the slider SL. A hole H or a tab TB is then provided for effecting connection at the point so determined. The strip PT is thus calibrated and can then be used in accordance with the invention for setting the transducer heads. Specification 819,789 is referred to.