Efficient active chatter mitigation for boring operation by electromagnetic actuator using optimal fractional order PD lambda controller

摘要

Due to the factor of limited rigidity of boring bars, small depths of cutting are normally applied for chatter free machining. Stability lobe diagrams can truly represent that limit. However, due to the presence of manufacturing inaccuracies like ovality and eccentricity, these limits are considerably changed. Hence, considering these during modelling the cutting process, stability analysis and controller design is a novel idea, hence implemented in the present work. Dynamic modelling of boring process is presented in detail using a 3-DOF model. Dynamics of such systems is represented using delay differential equations with time periodic coefficients. The system stability is enhanced with active control techniques. The closed loop system considering fractional order PD lambda in the loop is a nonlinear time periodic delay differential equation system. Any systematic controller synthesis process for such systems is rarely available in literature. It is observed that a fractional order PD lambda . controller designed by using combination of pseudo spectral and response optimization techniques is highly efficient in terms of the requirement of low amplitude of the peak force and simplicity of implementation. Transient vibrations can also be quenched in a limited period of time by using this controller. Different control techniques available in literature (H-infinity Loop shaping and PD control) are tested and compared to the proposed controller for enhancing the material removal rates and surface finish of the workpiece. By using the active chatter control, the chatter can be efficiently reduced and the material removal rate can be increased. The critical depth of cut is increased from 0.2 mm (open loop) to 0.6 mm (closed loop) with a limited actuator size in the case study.