Active vibration control via electromagnetic dynamic absorbers

An actively controlled electromagnetic absorber is considered for reducing the chatter in a boring bar. The absorber is suspended inside the free end of the boring bar and consists of a mass with four poles, each pole having a coil attached to it. In the present study, the magnetic force, which is inherently a nonlinear function of current and air gap, is approximated using linearized model. The dynamic characteristic of the boring bar is modeled using Timoshenko beam finite elements, while a lump parameter model is used for the absorber. Two approaches are used in the controller design. The first approach uses full state feedback with quadratic performance index. The second approach uses direct output feedback based on the results of the first approach. The effects of residual modes and spillover on the performance of the overall system are discussed for the two approaches. Simulation results show that a significant increase on the boring bar damping ratio can be achieved by using the proposed electromagnetic absorber.