Monitoring of machining processes and error motions for a high-speed air turbine microspindle

We develop a high-speed air turbine microspindle with a built-in microphone and pressure sensor to detect the breakage and wear of a micro-tool and to detect anomalies in the bearing and other spindle components. The results show that the spindle can detect variations in the microtorque (0.1 N·cm) and the frequency components of the rotation of the balls of the ball bearing. In addition, the effect of the external torque variation on the radial error motions of an air turbine microspindle is investigated. The results show that it is possible to measure the microtorque by measuring the change in the rotational speed of the spindle and that the radial error motions in the X and Y directions increase as the torque increases. In the case of the radial error motion in the X direction, the radial error motion is increased to approximately 0.007 μm per torque variation of 0.001 N·cm.