Using the skeleton method to define a preliminary geometrical model for three-dimensional speed reducers

This paper deals with the first design phase of three-dimensional speed red ucers. Concepts to help designers during the entry-level model definition a re presented and, more particularly, those related to the task of geometric al synthesis. From these principles, a specific CAD tool has been built and is also described. A rough model, called a skeleton, is introduced to repr esent each conventional reducing stage category, thus enabling the automati c formation of entire geometrical models of speed reducers. Shaft orientati ons and positions are calculated from products of transformation matrices, in the same way as for spatial kinematic chain closure conventional problem s. Optimisation techniques are used to obtain a preliminary dimensioning of the structure. The numerical processing is achieved progressively in three steps in order to improve the final convergence and, if necessary, to enli ghten further the designer on failure origins within specification data. Th ree examples are given to illustrate both the creation of the geometrical m odel and the way results are obtained.