Adaptive feedback system for controlling head/arm position in a disk drive

A method for adjusting a compensator in a feedback control system of a coupled plant, said compensator comprising an input summer, an output summer and first adjustable forward gain means for receiving signals from said input summer and providing signals to said output summer, at least one unit time segment delay means for receiving said signals from said input summer, at least second adjustable forward gain means for receiving signals from said at least one unit time segment delay means and for providing signals to said output summer, at least one adjustable back gain means for receiving signals from said at least one unit time segment delay means and for providing signals to said input summer, and an input to said input summer for receiving position error signals from an output of said plant, said method comprising the steps of:

• a. deriving a plurality of forward error values from position error signals fed to said input summer from said plant in response to a disturbance of said plant, said position error signals determined at plural, increasingly forward, time segment values;
• b. deriving a plurality of compensator output values from said output summer, said output values determined at said predetermined plural increasingly forward time segment values;
• c. applying as an input to said plant, said derived forward error values in a back propagation order that is in reverse time order to a time order in which said forward error values were derived;
• d. deriving plural back propagation error values in response to said applying of said derived forward error values in said back propagation order, said plural back propagation error values derived from output signals from said input summer;
• and
• e. employing said plural back propagation error values, said compensator output values and said position error signals to derive altered compensator gain means values which enable a reduction of said forward error values.