Mitigation of chatter instabilities in milling using an active fixture with a novel control strategy

Chatter vibrations in machining have collected the interest of several research activities in the last decades, mainly due to its detrimental effect on productivity and surface quality. Several approaches and techniques have been developed to mitigate the effect of these unstable vibrations, but the required expertise and setup time usually prevent the widespread industrial application. Retrofittable intelligent active fixtures, capable of monitoring the process in real-time and exert adequate counter-excitations, could allow to overcome some of these limitations. Nevertheless, the use of these devices was always limited to the mitigation of structural chatter vibrations, which are the ones generally fitting in the device bandwidth. This paper deals with the development of an active fixture using an alternative control strategy that exploits low-frequency excitations, with the purpose of mitigating the chatter vibrations at frequencies exceeding the device bandwidth. The paper covers the main aspects of the fixture design and mainly focuses on the theoretical and practical aspects of the followed approach for the control. An experimental tests campaign is finally discussed to show that the proposed approach is actually effective in mitigating chatter vibrations.