Experimental investigation on elastic joint robot dynamics

The investigation is a part of research on the dynamical behaviour of robots having "nonrigid transmissions" between motors and links. The experimental investigations are carried on by means of a planar 2 DOF prototype manipulator that has been designed and built at our Department. In previous investigations it was demonstrated (by computer simulations) that, from trajectories recordings, there are the possibilities to obtain what follows: (1) the identification of the stiffness and damping coefficients of the "non rigid" transmission; and (2) the computing of servomotors laws of motion that can minimize the trajectory errors due to the dynamic effects. For the above reported aims, we decided to use recordings of some points of the links trajectories, obtained by means of a digital television camera. So, we arranged a test rig that essentially consists of: (i) the planar prototype manipulator; (ii) a digital television camera, having high scanning rate in order to record link vibrations, connected to a PC; and (iii) software, developed at our department, by means of which it is possible to record planar trajectories from almost any possible position of the camera objective axis with respect to the working plane; this using just one camera. The paper describes the test rig and the early results obtained in the determination of the stiffness and damping coefficients.