Wide bandwidth control of high-speed milling machine feed drives

To fully realize the performance potential of high-speed milling it is necessary to design high-performance axis feed drives for use on high-speed milling machines. It is shown that a 40,000 rpm spindle demands an axis feed drive that is capable of providing 40 m/min feedrates, 20 M/s 2 peak accelerations with a 100 Hz servomotor control bandwidth to effectively utilize high cutting speeds when machining typical aerospace parts. These specifications significantly exceed the axis motion capabilities of conventional machine tools. Achieving this level of performance presents special design challenges for the feed drive components and for the axis control system. Solutions to some of the problems confronting the control system design for wide bandwidth feed drives are presented.; Wide bandwidth, machine tool axes often require special control system compensation to maintain stability in the presence of structural vibration modes that are inherent in the feed drive system. A control system design is presented that provides a 100 Hz position loop control bandwidth using a conventional ballscrew feed drive. The control system compensation provides stabilization for two torsional, vibration modes that are associated with the ballscrew transmission.; The large accelerations required for efficient, high-speed milling often cause undesirable axis rotation errors. This is especially true for compounded machine axes where the mass center of one axis changes with the position of the other axis or axes. A control system model that simultaneously controls the axis position and the yaw error for an axis with two, linear motors is presented. The control system model demonstrates a 45 times reduction in the yaw error for position commands requiring 10 M/s₂ average acceleration.; High-speed milling machines may not always require wide bandwidth position loop control on all of the machine axes. However, a machine with mismatched axis gains will suffer from excessive tracking error when executing multiple axis motions. A feedforward compensation that provides time delay equalization for the machine axes can reduce tracking errors by two orders of magnitude, for feed drives with a bandwidth ratio of 4:1, without extending the bandwidth of the axes.