An acoustic emission-based touch-off detection system has been developed to determine the relative orientation between a rotating micro-tool and a workpiece surface with micron-level accuracy. The system has been implemented on an existing 3-axis micro-scale machine tool (mMT). The system has been tested with micro-endmills as small as 50 μm in diameter and micro-drills as small as 254 μm in diameter. The accuracy of the system has been found to depend on tool geometry and workpiece surface characteristics and is generally on the order of one micron. An analytical model has been constructed to predict touch-off detection error. The calibrated model has been shown to predict surface overshoot and undershoot trends quite well. Simulations have shown that touch-off error is dominated by part surface roughness.

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