The concept of "difficulty" in mating operations

In order to optimize the assembly operations, an optimization index is necessary. In this line, the paper presents a new definition of difficulty for mating operations. This definition considers the geometry of the objects and the strategy used to mate the parts, so that both aspects can be evaluated for the ease of the task. Uncertainties can be considered in a natural way, just taking into account the statistical distribution of the parameters. The application of the definition is illustrated with an example of the cylindrical peg-into-hole assembly task.