Rolling bearing-suspended spindle run-out control using repetitive control and adaptive feedforward cancellation

Abstract

The wettability, friction, adhesion, and optical characteristics of a surface are affected by its micro-topography. In turn, the characteristics of a surface micro-topography can be determined by controlling the trajectory of a cutting tool mounted on a spindle. However, this method is constrained by the tool’s cutting accuracy, which is limited by the run-out error and thermal behavior of the spindle. In this work, an electromagnetic actuator (EMA) is installed at the end of the spindle to compensate for the spindle run-out error and the thermal displacement in real time. The spindle system model includes a cross-coupled stiffness and damping term for the ball bearings. Repetitive controller (RC) reduces the repeatable run-out (RRO) while adaptive feedforward cancellation (AFC) reduces the non-repeatable run-out (NRRO). The control system uses a zero phase error tracking controller (ZPETC) to compensate for its total phase delay. Experimental results show a 70% reduction in run-out error at rotation speeds of 6,000 rpm and 12,000 rpm. The thermal displacement in the radial direction is regulated within a range of 1 µm for more than 3 hours.