GB1361610A - Apparatus for playing disc records - Google Patents

Abstract

1361610 Automatic control of attitude PLESSEY CO Ltd 9 Aug 1970 [24 Aug 1970] 40592/70 Heading G3R [Also in Division G5] In an arrangement for reducing tracking error in a disc record player, a servo controlled system is provided for correcting detected deviations of the longitudinal axis of a pick-up arm from a tangential position with respect to the record groove being scanned as the pick-up stylus moves over a radius of the record. Pick-up arm 1 is horizontally pivoted at 4 and 5 to a bracket 2 which is vertically pivoted 3 on a carriage 11 which is driven by a servo motor along rails 13, 14 extending parallel to a radial path over the record. The bracket is connected by an extension 6 to an iron core 7 extending through coils 8, 9 and 10 mounted on the carriage. The middle coil 9 is connected to an oscillator and the two outer coils to a balance detector. The configuration is such that when the pick-up arm longitudinal axis is tangential to the groove being scanned the arm axis is at right angles to the carriage center line and the core is positioned to provide equal coupling between coils 9 and 8 and coils 9 and 10 so that the inputs to the detector are balanced. Any deviation upsetting the balance is detected and used to vary the speed of the servo motor to correct the error. When the pick-up stylus enters the record run out groove, the large out of balance output from the detector, greater than a predetermined level, is used to operate a trip mechanism which lifts the arm and returns it to its rest position. The inductive coupling shown can be replaced by a capacitive arrangement Fig. 4 (not shown).