Active control of low-frequency vibrations in ultra-precision machining with blended infinite and zero stiffness

In ultra-precision machining, vibration is the key factor which restricts the machining accuracy and surface quality of a workpiece. Using the traditional active negative-stiffness vibration control technology, the simultaneous suppression of the floor vibration interference and payload direct interference is difficult. The ability of the conventional vibration isolation system to inhibit the direct disturbance of a payload deteriorates during the suppression of the low-frequency interference, and the residual low-frequency vibration severely restricts further improvement of the machining accuracy. To solve this problem, this paper proposes a novel active vibration control method of absolute displacement feedback based on the blending of infinite and zero stiffness. The absolute displacements of the payload and floor are considered as the feedback signals, and through the series and parallel connections of positive and negative stiffness, the equivalent stiffness between an isolated payload and reference point and between the isolated payload and floor tends to infinity and zero, respectively. The infinite and zero-stiffness blending control is realized, and the direct interference of the payload and floor vibrations at low frequencies ( < 2 Hz) is effectively suppressed simultaneously. Finally, the effectiveness of the active vibration control method based on infinite and zero stiffness blending is verified by experiments. It is demonstrated to provide a good working environment for the precision and surface quality of ultra-precision workpieces. The active vibration control method proposed in this paper provides a feasible way to improve the performance of ultra-precision machine tools.