Stylus position sensor for video disc player apparatus

Claim 1

A video disc stylus carriage relative position sensing apparatus for generating a signal related to the stylus position within a supportive carriage comprising: first and second electrodes fixedly secured to a stylus carrying carriage; a third electrode having a fixed relation to said stylus and disposed between said first and second electrodes, said first and third and said second and third electrodes forming respectively first and second capacitors which vary in capacitance in accordance with the relative position of the stylus with respect to the carriage and wherein said stylus is mounted to permit relative movement between said stylus and the carriage; means for applying first and second phase related time varying signals to the first and second electrodes respectively, said first and second time varying signals being respectively coupled to the third electrode through the capacitance of the first and second capacitors respectively thereby providing a third signal at said third electrode, the phase and amplitude of said third signal being related to the relative position of the third electrode and thereby the stylus with respect to the first and second electrodes; and detection means responsive to said third signal for generating a substantially d.c. signal proportional to the position of the stylus relative to the carriage.