Development of an automatic cumulative-lead error measurement system for ballscrew nuts

Ballscrew is a precision mechanical component used to convert rotational motion to linear motion in the precision linear stage. The precision measuring system for the screw's cumulative-lead error is already well known. Up to now, however, there is no suitable measuring equipment for internal cumulative-lead error of the nut. For a matching pair, it is not reasonable to understand the quality of only one piece. This paper presents a developed automatic cumulative-lead error measuring system for ballscrew nuts. The nut is clamped by a rotational stage, in which the moving angle is detected by a rotary encoder. The probing ball is inserted into the nut and remains in contact with the thread groove of the nut. The probe arm is mounted on a linear slide so that when rotating the nut, the probing ball will be pushed by the groove wall and moved axially. A high-resolution diffraction scale is employed to detect the linear movement of the probe to nanometer resolution. Combining the angular and linear motions, the cumulative-lead error of the nut can be realized. In practice, however, the nut will cause typical spindle errors during rotating, including axial slip, radial run out, and tilt motions. These errors have to be compensated in order to guarantee the accuracy of measurement results. A multi-sensor error compensation system is thus developed. Experimental results show the applicability of this developed measuring system.