Video disc stylus position sensor system

An apparatus for sensing the relative position of a first element relative to a second element comprising:

• a first electrode in fixed relation with the first element and constrained to move therewith;
• second and third electrodes in fixed relation with the second element and disposed on either side of the first electrode, said first and second electrodes forming a first variable capacitance and said first and third electrodes forming a second variable capacitance;
• a time varying signal source;
• first and second similar variable impedance means;
• means connecting the first variable impedance means in a first serial impedance combination with said first variable capacitance such that the impedance value of said first variable impedance is varied synchronously by said time varying signal source, respectively increasing and decreasing in impedance value with first and second polarity signals;
• means connecting the second variable impedance means in a second serial impedance combination with said second variable capacitance such that the impedance value of said second variable impedance is varied synchronously by said time varying signal source, respectively decreasing and increasing in impedance value with said first and said second polarity signals;
• said first and second serial impedance combinations being in parallel connection with respect to the first electrode;
• signal pickup circuitry responsive to impedance values, said circuitry connected to said first electrode for generating a control signal indicative of the impedance value of the parallel connection of the first and second serial impedance combinations as a function of the relative position of the first element relative to the second element.

In combination:

• a video disc signal pickup stylus secured to a stylus arm compliantly mounted to a carriage assembly for translating the pickup stylus radially across a record disc;
• first and second electrodes secured in fixed relation to the carriage assembly proximate the pickup stylus and on either side thereof;
• a third electrode disposed between said first and second electrodes and having a fixed relation to the pickup stylus and forming first and second capacitors with said first and second electrodes respectively, the capacitance values of said first and second capacitors varying in accordance with the relative position of the pickup stylus with respect to the carriage assembly;
• means for applying an AC signal;
• first and second means respectively connecting the first and second electrodes to the means for applying an AC signal;
• a first voltage variable capacitance connected between the first electrode and a point of fixed potential, said first voltage variable capacitor increasing in capacitance with increasing potentials of a given polarity applied to the first electrode;
• a second voltage variable capacitor connected between the second electrode and said point of fixed potential, said second voltage variable capacitor decreasing in capacitance with increasing potential of said given polarity applied to the second electrode, the first and second voltage variable capacitors modulating the amplitude of the signals appearing at the first and second electrodes in complementary fashion;
• and
• circuitry connected to the third electrode, responsive to the signals coupled thereto from said first and second electrodes for generating a control signal in accordance with the relative position of said third electrode with respect to the first and second electrodes to control the translation of the carriage assembly.

In combination:

• a video disc signal pickup stylus secured to a stylus arm compliantly mounted to a carriage assembly for translating the pickup stylus radially across a record disc;
• first and second electrodes secured in fixed relation to the carriage assembly proximate the pickup stylus and on either side thereof;
• a third electrode disposed between said first and second electrodes and having a fixed relation to the pickup stylus and forming first and second capacitors with said first and second electrodes respectively, the capacitance values of said first and second capacitors varying in accordance with the relative position of the pickup stylus with respect to the carriage assembly;
• means for applying an AC signal;
• a first voltage variable capacitance connected in a first serial combination with said first capacitor;
• means connecting the first voltage variable capacitance to the means for applying an AC signal for increasing its capacitance with increasing potentials of a given polarity of said AC signal;
• a second voltage variable capacitance connected in a second serial combination with said second capacitor;
• means connecting the second voltage variable capacitance to the means for applying an AC signal for decreasing its capacitance with said increasing potentials of a given polarity of said AC signal;
• and
• circuitry connected to the third electrode, said circuitry being responsive to the changes of capacitance of the first serially connected capacitor combination with respect to capacitance changes of the second serially connected capacitor combination for generating a control signal indicative of the relative value of the first and second capacitors and thereby the position of the signal pickup stylus with respect to the carriage assembly.