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System modeling and robust control of an AMB spindle : part II a robust controller design and its implementation

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This paper discusses an entire procedure for a robust controller design and its implementation of an AMB (active magnetic bearing) spindle, which is part II of the papers presenting details of system modeling and robust control of an AMB spindle. Since there are various uncertainties in an AMB system and reliability is the most important factor for applications, robust control naturally gains attentions in this field. However, tight evaluations of various uncertainties based on experimental data and appropriate performance weightings for an AMB spindle are still ongoing research topics. In addition, there are few publications on experimental justification of a designed robust controller. In this paper, uncertainties for the AMB spindle are classified and described based on the measurement and identification results of part I, and an appropriate performance weighting scheme for the AMB spindle is developed. Then, a robust control is designed through the mixedμ synthesis based on the validated accurate nominal model of part I, and the robust controller is reduced considering its closed loop performance. The reduced robust controller is implemented and confirmed with measurements of closed-loop responses. The AMB spindle is operated up to 57,600 rpm and performance of the designed controller is compared with a benchmark PID controller through experiments. Experiments show that the robust controller offers higher stiffness and more efficient control of rigid modes than the benchmark PID controller.

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A :

System matrix

C(s) :


d :

Plant input disturbance

D :

D scaling for theμ synthesis

e :


F l :


G.G(s) :


M :

General plant

n :


S :

Sensitivity function

T :

Complementary sensitivity function

U :

Controller input

w :

Controller input disturbance

W :

Weighting functions

δ :

Parameter variation

ω :

Natural frequency

ξ :



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Correspondence to Hyeong-Joon Ahn.

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Ahn, H., Han, D. System modeling and robust control of an AMB spindle : part II a robust controller design and its implementation. KSME International Journal 17, 1855–1866 (2003).

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Key Words

  • Robust Control
  • Uncertainty Description and Active Magnetic Bearing