Even though assembly of heavy works (10Kg to 10ton) is a dangerous task, it has not been automated. After analysing the assembly process of heavy parts, the combination of a crane and a robot is proposed in this paper. In order to avoid an impact force between parts, compliance is installed on the tip of the robot. A heavy work is suspended by a crane: it is moved by the robot and the wire is fed. The stiffness matrix is obtained about the suspended work. The vibration is absorbed at the positioning. Experimental results of the control indicate that the system is efficient. © 1990 CIRP.