| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 99 === Ballscrew is a precision mechanical component serving to convert rotational motion to linear motion in a precision linear stage. The measuring system for the screw’s accumulative lead error can be found on the market. Up to now, however, there is no suitable measuring machine for accumulative lead error measurement of the nut. It is known that this error directly reflects the grade of the nut.
This paper presents a developed automatic accumulative lead error measuring system for ballscrew nuts. Similar to the screw measuring system, the nut is clamped by a rotational stage and the probe ball is in contact with the groove of the nut. The probe is mounted on a cross roller table so that when rotating the nut the probe ball will be pulled by the groove wall and moved axially. A high resolution diffraction interferometer scale will read the linear movement of the probe to nanometer resolution. Combining the angular and linear motions the accumulative lead error can be realized.
In practice, however, the nut will experience axial slip, radial run-out, and tilt during the motion. These spindle-like rotating induced errors have to be compensated in order to guarantee precise measurement results. Based on the derived theoretical model of axial slip, the axial runout could be measured by placing capacitive displacement sensors to acquire the translational displacement of the spindle and the angle of the pitch. Furthermore, a sensor gap measurement system associated with a servo piezoelectric actuator stage has been developed for the purpose of radial runout compensation. A microprocessor based PID controller is established to real-time adjust the probe ball’s vertical position so as to remain contact with the nut groove.
Experimental results will show the applicability of this developed measuring system.
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