The influence of friction on the dynamic model for a 6-DOF parallel robot with triangular platform

The dynamic analysis is an important element of the mechanical design and control of parallel mechanisms. This paper presents a method for the dynamical modeling of the guided in three points parallel robots with six degrees of freedom having triangular platform, including the friction. The evaluation of the full generalized forces is performed in two stages. In the first stage, the drive generalized forces are established, based on the dynamical equations without friction. Using the Newton-Euler equations, the reactions from each joint are computed. In the second stage the additional drive generalized forces due to the frictions from the active and passive joints are computed by means of two approaches. The first approach considers the whole mechanism. The generalized additional forces which include the friction effect from the corresponding drive joints and the friction effect from all passive joints are calculated using principle of virtual power and the mechanism Jacobi matrices. The second approach treats the kinematic chains as independent. The generalized additional forces are evaluated using the virtual work principle. In both approaches the passive joints are approximated with compliant joints whose momentum are equal to the friction torques of these joints