Head positioning servo for disk drives

DETAILED DESCRIPTION There is disclosed a positioning apparatus for positioning a magnetic head in a disk drive comprising: the magnetic head to be positioned; a positioning servo for positioning the head; and, a driver circuit for driving the positioning servo by controlling the position of the head as a function of time.
Head position is controlled as a function of time in accordance with a predetermined profile or schedule of position data versus time.
The profile also defines both the velocity and acceleration as a function of time throughout the seek movement.
The driver circuit compares the actual position of the head to the predetermined profile to generate an error signal based upon the time difference.
The predetermined profile contemplates controlled acceleration at all times during the seek, i.
e.
, the acceleration is constant and positive during the first portion of the seek and constant and negative during a second portion of the seek.
For seeks of any length greater than a predetermined number of tracks, the acceleration is constant during a first portion of the seek, the acceleration is zero during a middle portion of the seek, and the acceleration is constant and negative during the last portion of the seek.
The servo driver of the positioning apparatus utilizes a midpoint counter which stores data loaded by a microprocessor regarding the length of a particular seek.
The midpoint counter counts signals related to track crossings generated by nonvolatile memory driven by a counter to determine when the midpoint of a seek is reached whereupon a midpoint signal is generated.
The seek is started when a counter control circuit starts a data counter counting the count up mode.
The counter data outputs serve as the address signals for the memory which stores the profile data.
Two data outputs from the memory carry pulses resulting from the stored profile data.
The spacing between these pulses decreases as time goes by until the midpoint signal is generated.
One of the pulse trains has twice as many pulses as the other, and is used by the midpoint counter to determine when the midpoint of the seek has been reached