A translation axis assembly includes a supporting arm, a connecting plate, and a center-of-gravity adjusting device connected between the supporting arm and the connecting plate. The center-of-gravity adjusting device is configured to adjust a position of the supporting arm on the connecting plate to adjust a center of gravity of the translation axis assembly. The center-of-gravity adjusting device includes a locking assembly configured to allow the supporting arm and the connecting plate to be in a loose fit or to hold tightly to each other.