Abstract
The air spindle is an essential machine element of the ultraprecision machine tool because of its high rotational accuracy and low spindle vibration. The size of works machined on the ultraprecision machine tool become smaller, and the diameter of the tools employed are also be decreased. For obtaining suitable cutting speed with these small tools, the rotational speed of the tool spindle of the machine tool should be increased. As a result, a high-speed air spindle with low vibration should be developed. In the present paper, we propose a new tactics for suppressing the spindle vibration at high rotational speed. An active aerodynamic bearing is incorporated into the air spindle supported by ordinary aerostatic bearings. In this hybrid bearing system, spindle weight and cutting load are basically supported by the aerostatic bearings and the spindle vibration in the high speed range can be controlled by the active aerodynamic bearing. A displacement sensor detects the spindle vibration and according to the detected vibration, a microcomputer controls the wedge angle of the aerodynamic bearing by using a piezoelectric actuator incorporated. The load carrying capacity of the aerodynamic bearing increases as the rotational speed of the spindle, therefore the proposed active aerodynamic bearing is effective in higher rotational speed of the spindle. The concept of designing of the active aerodynamic bearing and some results of experiments obtaining by a test model spindle are reported.
