Locked groove detection and correction in video disc playback apparatus

In video disc playback apparatus for use with a video disc having a spiral information track containing representations of recorded composite video signal information inclusive of regularly recurring sync signals with sync signal recording locations non-radially aligned in successive convolutions of the spiral track;

• said playback apparatus including a signal pickup for sensing said information representations alone said spiral information track as said disc is rotated, and means coupled to said signal pickup for providing a composite video signal output corresponding to the recorded information sensed by said signal pickup, wherein normal operation involves the sensing of said information representations along successive convolutions of said spiral track in a regular progression toward one spiral extremity;
• the combination comprising:
• means, responsive to the composite video signal output of said output providing means, for separating said sync signals from other components of said composite video signal;
• a voltage controlled oscillator;
• a phase detector, responsive to said separated sync signals and to an output of said oscillator, for developing an output having an amplitude and a polarity indicative of the magnitude and sense, respectively, of departures, if any, from a predetermined phase relationship between said separated sync signals and said oscillator output;
• a low pass filter responsive to said phase detector output for developing an error voltage;
• means for applying said error voltage to said oscillator to vary the frequency thereof in a direction tending to oppose said departures from said predetermined phase relationship;
• means for developing an output pulse indicative of a disruption of said regular progression by a shift of the radial location of said signal pickup sensing in a direction away from said one spiral extremity;
• said output pulse developing means including a voltage comparator responsive to said error voltage and providing said output pulse only when said error voltage is indicative of a given sense of departure from said predetermined phase relationship and reaches an amplitude exceeding a selected threshold level;
• means for shifting the radial location of sensing by said signal pickup in a direction toward said one spiral extremity;
• means responsive to output pulses provided by said voltage comparator for actuating said shifting means;
• wherein said actuating means includes:
• a normally disabled drive pulse generator;
• means for enabling said drive pulse generator in response to the appearance of a plurality of input impulses within a time period of selected duration;
• means responsive to output pulses provided by said voltage comparator for developing said input impulses;
• and
• means for supplying the output of said drive pulse generator to said shifting means.

In a video disc record player for use with a video disc record having a spiral groove in a band encircling the center of said disc, said spiral groove containing an information track comprising geometric variations along the bottom of said groove representative of recorded composite video signal information inclusive of horizontal sync signals nominally recurring at a given line repetition rate, the sync signal recording locations in said track being spirally aligned in successive convolutions of said groove spiral;

• said player including (1) a stylus, having a tip subject to reception in said groove, and forming a capacitance with said disc which varies in accordance with the geometric variations of said track passing beneath said stylus as said disc is rotated, (2) a pickup arm upon which said stylus is mounted, and (3) means responsive to said capacitance variations for recovering the recorded composite video signals;
• the combination cmprising:
• a sync signal separator for separating said horizontal sync signals from said recovered composite video signals;
• an oscillator;
• means for developing an error voltage indicative of the magnitude and sense of deviations from a given phase relationship between said separated horizontal sync signals and an output of said oscillator;
• means for controlling the frequency of said oscillator in accordance with said error voltage;
• a voltage comparator coupled to said error voltage developing means for developing an output impulse only when said error voltage is indicative of a given deviation sense and exceeds a given amplitude;
• a staircase voltage generator;
• a normally disabled purse generator subject to being enabled when the output of said staircase voltage generator exceeds a selected threshold level;
• means for effecting a movement of stylus toward said disc center, said movement effecting means being subject to actuation upon said enabling of said pulse generator;
• and
• means responsive to the output of said voltage comparator for pulsing said staircase voltage generator.

In video disc playback apparatus for use with a video disc record having a spiral groove in a band encircling the center of said disc, said spiral groove containing an information track comprising geometric variations along the bottom of said groove representative of recorded composite video signal information inclusive of horizontal sync signals nominally recurring at a given line repetition rate, the sync signal recording locations in said track being spirally aligned in successive convolutions of said groove spiral, said playback apparatus including (1) a stylus, having a tip subject to reception in said groove, and forming a capacitance with said disc which varies in accordance with the geometric variations of said track passing beneath said stylus as said disc is rotated, (2) a pickup arm upon which said stylus is mounted, and (3) means responsive to said capacitance variations for recovering the recorded composite video signals;

• wherein normal operation of said playback apparatus involves stylus traversal of successive convolutions of said groove spiral in a regular progression toward one spiral extremity;
• the combination comprising:
• means, responsive to the recovered composite video signals, for separating said horizontal sync signals from other components of said recovered composite video signals;
• a voltage controlled oscillator;
• a phase detector, responsive to said separated sync signals and to an output of said oscillator, for developing an output having an amplitude and a polarity indicative of the magnitude and sense, respectively, of deviations from a given phase relationship between said separated sync signals and said oscillator output;
• a low pass filter responsive to said phase detector output for developing an error voltage;
• means for applying said error voltage to said oscillator to vary the frequency thereof in a direction tending to oppose said deviations from said given phase relationship;
• and
• means for developing an output pulse indicative of a disruption of said regular progression by a shift of the radial location of said stylus in a direction away from said one spiral extremity;
• said output pulse developing means including a voltage comparator responsive to said error voltage and providing said output pulse only when said error voltage is indicative of a given sense of deviation from said given phase relationship and reaches an amplitude exceeding a selected threshold level.