Magnetic servo with improved tracking system

Abstract

A two-part head positioning system has a tracking motor for moving the head through relatively small distances so that it follows the track of a medium and moves between adjacent tracks and a seek motor for moving the tracking motor and head through relatively large distances between non-adjacent tracks. The system has been improved by mechanically isolating the seek motor from the tracking motor so that small movements from the tracking motor are not transmitted to or from the seek motor and the arm between that motor and the tracking motor. The tracking motor and the mechanical isolator are in one unit. A magnet is mounted on the head support, which extends from the tracking motor to the head. This magnet is positioned within an electromagnetic coil that is mounted within magnetic shielding and fixed to the arm extending to the seek motor. Selective energization of the electromagnetic coil moves the magnet and the head support laterally in the coil. Flexures extend between the magnetic shield and the head support and allow relatively free movement of the head support under control of the magnetics perpendicular to the tracks of the medium but no movement along any other axis or pivoting about any axis. Different configurations for the magnetic shield and the flexures are disclosed. The tracking motor can also be controlled in that the position of the head support relative to the arm is a function of the current to the tracking motor. By proper connection of the servo loops, noise and other extraneous portions of the position error transfer function are cancelled. A filter may be used to cancel noise created by the seek motor. A system for shorting the tracking motor to restore it to its null position and using induced current generated by the tracking motor to hold the tracking motor in its null position is also disclosed.