Speed regulation of an eccentric rotor with a flexible joint

This article explores the problem of speed regulation of an unbalanced rotor in gravitational field with a flexible shaft. This problem falls into the category of vibration control of flexible structures subject to nondecaying harmonic disturbances. The experimental device is an eccentric rotor driven by a dc servomotor through a flexible joint. As the eccentric rotor revolves at the set speed, a gravitational harmonic torque is imposed on it. The fact that the actuator is not collocated with the output, nor with the harmonic disturbance, poses a challenge in control design. A novel control algorithm is developed to emulate the dynamics of a set of passive mechanical springs, damper, and mass. By integration of the virtual elements with the flexible joint, a virtual vibration absorber is devised with respect to the payload. The nondecaying disturbance can be counteracted by the virtual vibration absorber since it introduces the characteristic mode of the disturbance into the control loop. Effectiveness of the control scheme is demonstrated by both numerical simulations and realtime experiments.