Online chatter suppression in turning by adaptive amplitude modulation of spindle speed variation

Although the effectiveness of spindle speed variation (SSV) method in chatter suppression has been extensively reported, the determination of optimal SSV parameters remains a challenge owing to the difficulties in obtaining accurate modal parameters especially under varying cutting conditions. This paper proposes a closed-loop SSV cutting system to suppress chatter in turning. The dimensionless SSV amplitude is adaptively adjusted with a model-free controller to accommodate change of the chatter level. The wavelet packet entropy (WPE) is computed online to evaluate quantitatively the machining state, and a predetermined chatter threshold is used to calculate the controller input. Energy-based analysis of SSV parameters effect on chatter shows that the amplitude is the more dominant parameter than the frequency. Then we introduce the scheme of the proposed chatter suppression system, where the Bootstrap method is adopted to determine the threshold value. Next, the feasibility of the proposed method for chatter suppression is tested by simulations with different cutting depths. Finally, comparisons of experimental results verify the conclusion of theoretical analysis about the effect of SSV parameters, and two cutting tests with diverse activating strategies are performed to validate the effectiveness of the proposed system for chatter suppression in turning.