Ultra-light and ultra-accurate portable coordinate measurement machine substantially immune to bearing assembly thermal effects

Abstract

A coordinate measurement machine (CMM) includes a manually-positionable articulated arm. The articulated arm includes arm segments and rotary joints. At least one of the rotary joints includes a bearing assembly that comprises first and second bearings, a shaft that engages an inner race of the first bearing and an inner race of the second bearing, a housing that engages an outer race of the first bearing and an outer race of the second bearing, and a transducer configured to output an angle signal corresponding to an angle of rotation of the shaft relative to the housing. The shaft and the housing may be fabricated from materials having coefficients of thermal expansion selected to minimize change in moment rigidity and/or radial rigidity of the bearing assembly as the ambient temperature changes from the lower limit to the upper limit of the CMM operating ambient temperature range.