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A high-speed precision air-bearing tool spindle with active aerodynamic bearing is proposed for improving the quality of machining using small-diameter cutting and grinding tools. The spindle is basically supported by aerostatic radial and thrust bearings. According to the spindle vibration detected by capacitance sensors, the wedge angle of the active aerodynamic bearing was controlled using piezoelectric actuators, thereby suppressing the spindle vibration. In the present paper, the performances of a prototype air-bearing spindle with single-row active aerodynamic bearing and an improved air-bearing spindle with double-row bearings are reported. Through experiments, it was demonstrated that the maximum rotational speed controlled by the active aerodynamic bearing is 800 Hz (48,000 min-1), and that the amplitude of spindle vibration can be suppressed to -1).

A novel high speed air-bearing spindle is proposed as a tool spindle for small diameter of cutting and grinding tools. The spindle vibration at high rotational speed is suppressed by an active aerodynamic bearing incorporated into the spindle. For generating aerodynamic damping force, the wedge angle on the aerodynamic bearing surface is controlled by piezoelectric actuators. By using several control tactics, the effect of the active control of the aerodynamic bearing on the spindle vibration is analyzed. Experimental result shows that the amplitude of the spindle vibration can be suppressed to be 0.1μm at the rotational speed of 50,000 min1 (833Hz). Final goal of the study is to suppress the amplitude of spindle vibration less than 0.1 μm at the rotational speed of 120,000 min1 (2kHz).

For ultraprecision applications, two types of active control restrictors for aerostatic bearings are evaluated. The first restrictor is called an aerostatically controlled restrictor (ACR), a bearing-pressure-feedback type. The change in the pressure on the bearing surface directly controls the restriction gap, and the stiffness of the aerostatic bearing with the ACR can be infinite. The second restrictor is called an active inherent restrictor (AIR), a bearing-gap-feedback type. The change in the air-gap on the bearing surface is detected by an electric sensor, and then an electric actuator controls the restriction gap. By using the AIR, infinite bearing stiffness and nanometer-order of rotational accuracy of the spindle can be realized. Positioning with subnanometer order of resolution can also be executed by an aerostatic guideway with the AIR.