Transducer arm assembly for disk play-back machines

A disk play-back machine comprising

• a base plate supporting, a platform rotatable about a first axis in a plane parallel to said base plate, a record disk resting upon said platform for concentric rotation about said first axis in a plane parallel to said base plate, and a first plane, containing the uppermost spirally grooved surface of said record disk,
• a transducer arm defining a second plane which is perpendicular to said base and having a transducer, supporting a stylus at a first end and having second axis means at a second end and wherein said transducer arm is adapted for pivoting and sliding movement from a first acute angle position to a second acute angle position parallel to said platform wherein said pivoting movement takes place about said second axis means and wherein said second axis means is adapted to slide in a third plane which is parallel to and intersects said first axis and wherein said first and second acute angles are formed by said transducer arm and said third plane,
• a transducer arm support carriage and low friction guide means therefor, adapted to enable said second axis means to slide from a first position to a second position in said third plane and in a first direction toward said first axis in direct response to electric motor drive means wherein the position of said transducer arm support carriage is continually adjusted in order to keep said transducer arm tangent to any groove radius at the point where said stylus contacts said rotating record disk, and wherein said electric motor drive means is started and stopped in response to an error signal generated by an error detecting pair consisting of a magnet and a differential Hall Effect generator and wherein one or the other of said error detecting pair occupies a fixed position in relation to said transducer arm such as to pivot about said second axis means every time said transducer arm pivots about said second axis means,
• and wherein the improvement comprises true position indicating means being rotatable about said second axis means along with said transducer arm but independently from the latter and being adapted to mount one or the other of said error detecting pair wherein said true position indicating means is adapted to rotate in a plane parallel to said first plane and toward a unique and particular angular position of substantially infinite resolution with respect to every unique and particular linear position of substantially infinite resolution of said second axis means, while the latter is being transported from said first position to said second position by said transducer arm support carriage and wherein the combination of rotation and sliding of true said position indicating means is substantially identical to the theoretical combination of rotation and sliding of said second plane of said transducer arm, parallel to said first plane while said second axis means slides from said first position to said second position necessary to keep said second plane tangent to any of said groove radii between a maximum and a minimum groove radius at any of the points where said stylus makes said contact with said groove.