Development of the control system for three-axis ultraprecision compact micromilling machine

In order to overcome the nonlinearity of the conventional servomechanism driven by ball screws, coreless linear motors are directly used to drive air bearing slides. Linear encoders with a resolution of 1.2 nm are used as position feedbacks. A dynamics model is established for stacked X-Y stages, and the system resonance is then theoretically analyzed and experimentally verified. In order to improve the performance of the stacked stages, a compound proportional-integral-derivative controller with a notch filter is developed using zero-pole assignment and model parameter matching method. Experimental results show that the controller developed can work to reduce the mechanical resonance caused by the cross-coupled stiffness, and the minimum positioning resolution of the micromilling machine is 20 nm. To track a sinusoidal signal with a frequency of 30 Hz and an amplitude of 5 μm, the phase lag is less than 10° and the amplitude attenuation is less than 10% for all the three axes.