Multi-stage servo control design system

A method comprising:

• designing two controllers in a first dual-stage including:
• measuring a first output of a first plant corresponding to a first actuator;
• measuring a second output of a second plant corresponding to a second actuator;
• designing a first controller responsive to the first output;
• designing a second controller responsive to the second output;
• and
• combining the first output and the second output to obtain a first combined output;
• measuring an open-loop of the first dual-stage;
• designing two controllers in a second dual-stage including:
• designing a third controller responsive to the first combined output;
• measuring a third output from a third plant corresponding to a third actuator;
• and
• designing a fourth controller responsive to the third output;
• and
• combining the first combined output and the third output to obtain a second combined output;
• and
• comparing the second combined output with a reference input to provide closed loop positional control of a magnetic head.

An apparatus comprising:

• a read/write channel configured to communicate with multi-stage actuators that position a read/write head, the multi-stage actuators modeled as a plurality of plants;
• and
• a servo controller coupled to the read/write channel to monitor magnetic head position signals, the servo controller comprising:
• a plurality of controllers configured responsive to output signals for the plurality of plants, including:
• a first controller, the first controller configured responsive to a first output signal for a first plant, and a second controller, the second controller configured responsive to a second output signal for a second plant, in a first dual-stage;
• and
• a third controller, the third controller configured responsive to a first combined output signal including the first output signal and the second output signal, and a fourth controller, the fourth controller configured responsive to a third output signal, in a second dual-stage.