This paper describes a compensation method for elastic and thermal deformations of the machine frame supporting the mechanism of the parallel kinematic machine (PKM). In the proposed method, three displacement sensors with Super-Invar rods measure distance variations among three joint supports connecting the mechanism. Thus, the base platform's dimensions of the PKM are calculated from these measured distance variations. Moreover, six other displacement sensors with rods measure the distance variations between the machine's surface plate and the three joint supports. Therefore, the forward kinematics of the hexapod mechanism calculates displacement and attitude variations of the base platform during operation from these measured displacements. Consequently, coordinates of the PKM's end effector can be compensated by the dimensions, the displacement, and the attitude of the base platform during operation. This device was installed in an experimental coordinate measuring machine using a three-degree of freedom parallel manipulator. Coordinate measurements using a master ball mounted on the surface plate showed that this device decreased the influences of temperature fluctuation and external force on machine accuracy.
