GB1461848A - Record pickup velocity correction - Google Patents

Abstract

1461848 Pickup positioning device RCA CORPORATION 10 April 1974 [16 April 1973] 15792/74 Heading G5R To oppose undesired cyclic variations, within a given error frequency range, in the relative velocity between a pickup stylus (12), Fig. 1 (not shown), and a rotating grooved record disc 4, a transducer 24 is mechanically coupled to the stylus to vary the position thereof in response to a correction signal, the transducer having an electrical winding 80 located on a first portion and energizable by said signal to produce relative movement between said first portion and a magnetic flux-generating second portion coupled by resilient means 72 to the first portion, and electrical damping means 78 operative to oppose such movement, the transducer having a natural mechanical resonance at a frequency within said error frequency range. The movable member of the transducer comprises a non-magnetic, non-electrically conductive cylinder 56 joined to a stylus support arm 22 by a coupling, which is rigid longitudinally of arm 22 but allows vertical and lateral movement thereof, and connected by resilient annular member 72 to a sleeve 70 fixed on an arm 50 projecting from a permanent, or electro-, magnet 42 providing a flux gap 48 in combination with iron members 40, 46. The winding 80 is provided around or under a closed loop metal band forming the damping means 78. The transducer 24 is located in a conductive housing driven so that the stylus (12) on arm 22 tracks a video disc 4 radially. The disc 4 comprises a dielectric coating (6), Fig. 2 (not shown), over an electrically conductive layer (8) on a dielectric substrate (10) and has a spiral groove engaged by stylus (12) which carries a conductive electrode (14) forming a varying capacitance with layers (6), (8) to effect playback. To correct for errors due to the disc turntable speed, disc eccentricity or recording errors, winding 80 is supplied with an error voltage provided by a frequency discriminator/amplifier circuit responsive to deviations from a norm in the horizontal sync. pulse frequency of the replay signal. Alternatively, if only turntable speed errors are to be corrected, the error voltage may be provided by an optical detector in conjunction with a deflecting pattern on the turntable. The arrangement may be applied to apparatus having a nominally constant turntable angular speed, e.g. 450 r.p.m., or one in which the turntable speed varies to maintain a nominally constant groove velocity at the stylus (12).