An investigation of spectral characteristic of displacement fluctuation and its effect on surface quality in precision machining

In precision machining, the machining conditions play an important role in part surface quality, because the characteristic of the exciting source in machine tools has a close relationship with the machining conditions. Therefore, this paper investigates the spectral characteristic of displacement fluctuation and its effect on the part surface quality for ball screw feed systems. The spectral characteristic is deduced by an equivalent disturbance model that considers the error sources of permanent magnet synchronous motor drives. In the spectrum of displacement fluctuation, the amplitudes of some spectral components increase with the load force; the corresponding frequencies are even multiples of the fundamental frequency of phase current and of the fundamental frequency of phase current plus or minus the rotor frequency. The resonance due to the variation of spectrum seriously deteriorates the part surface quality, leading to visible and characteristic patterns on the surface of machined parts. In the paper, two solutions to improve the surface quality are proposed and validated, i.e., the control method based on an adaptive filter and the method with constraint of feed rate.