Patent ID: 8316728

Claim:
An actuator for selectively extending and retracting a probe in a measuring instrument comprising: an actuator body a lead screw disposed within the actuator body; a lead screw nut mated with the lead screw; a carriage, having a first aperture slidably engaging the actuator body; a first and second interengaging kinematic mount members attached to the carriage and the actuator body respectively for accurately positioning the carriage with respect to the actuator body when the carriage is in an extended position, one of the first and second interengaging kinematic mount members comprising a hemispherical bearing; a first plurality of magnets disposed around an inner circumference of the first aperture; the carriage also including a second aperture engaging a probe holder having a probe attached thereto; and a second plurality of magnets arranged on a periphery of the lead screw nut, generally aligned with the first plurality of magnets, the first and second pluralities of magnets arranged so that the carriage may be displaced with respect to the actuator body a sufficient amount that the first and second pluralities of magnets do not significantly restrain the movement of the carriage relative to the actuator body.