Critical control design for fatigue avoidance in two-inertia systems

A control system design for two-inertia resonant systems that takes account of shaft torsion is proposed. On the basis of elementary knowledge of material mechanics, we derive an inequality condition for avoiding metal fatigue of a shaft. To satisfy the derived condition as well as other constraints, the critical control method is employed to design a feedback controller. The disturbance observer and minor velocity feedback are also used to improve the damping factor of the nominal plant. An illustrative design example using a laboratory test bed shows that the elastic shaft never fatigues how many times it twists during operation.