Abstract : This work proposes a method for mechanism design based on a hierarchical decomposition of synthesis tasks. Among the identified tasks, what we are most interested in is the one which carries out the choice and optimal dimensioning of the "Technological Devices ensuring a Mechanical Joints". These TDMJ are high level features which have all the required attributes for independent processing. However, the recombination of the system can reveal some conflicts between the joints. The overall synthesis is expressed in the form of a hierarchical optimization problem for which we propose several methods of resolution, among which a method of collaborative optimization. We present a tool for assistance which, once coupled with a commercial CAD software, enabled us to validate the concepts. Some examples illustrate our discussion.