  Starting from the definition of a stiffness matrix, the authors present a new
formulation of the Cartesian stiffness matrix of parallel mechanisms. The
proposed formulation is more general than any other stiffness matrix found in
the literature since it can take into account the stiffness of the passive
joints, it can consider additional compliances in the joints or in the links
and it remains valid for large displacements. Then, the validity, the
conservative property, the positive definiteness and the relation with other
formulations of stiffness matrices are discussed theoretically. Finally, a
numerical example is given in order to illustrate the correctness of this
matrix.
