Modeling and control simulations of a slewing frame containing active members

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Abstract
A testbed consisting of a flexible frame slewed by a DC motor is modeled for active vibration suppression. This presents a challenging control problem since the primary action of slewing induces both bending and torsional vibrations in the structure. Inserted into the frame are two active members that can be used as self-sensing actuators in feedback control loops. First, a model for the slewing frame is developed using Lagrange's equations and finite element approximations. The interactions between the structure and the slewing actuator are then derived from the equations for a DC motor. Similar expressions are obtained for the forces applied to the structure by the active elements. A detailed model of the self-sensing actuator is provided, which includes the terms due to actuator and sensor dynamics. A theoretical study is then conducted to obtain control laws that simultaneously slew the frame and suppress the residual vibrations. Simulation results indicate that the DC motor is effective in slewing the frame and suppressing the bending motion but not the torsional motion. Hence, the torsional vibrations are suppressed using the active members in collocated feedback loops.

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