Spherical linkages are constituted entirely of revolute pairs. A spheric pair would produce no additional constraints and would thus be equivalent to an opening in the chain, while all other lower pairs have nonspheric motion.
球面连桿完全是有转动副组成。一个回转副不会产生额外的约束,因而就相当于开式链,而所有其它的低副都有非球形运动。