END-EFFECTOR REGULATION OF ROBOTS WITH ELASTIC ELEMENTS BY AN ITERATIVE SCHEME

The regulation of motor variable positions in robots with elastic elem ents has been solved using PD linear controllers in the absence of gra vity and with the addition of a model-based feedforward term when grav ity is present. When the mass of the links is not known, an iterative learning scheme can be derived to obtain the same result for both join t elasticity and link flexibility. An extension to end-effector regula tion with a similar two-stage and hence time-consuming scheme has been proposed. In this paper we show the feasibility of a new iterative on e-stage scheme able to directly regulate the end-effector position in robots with joint elasticity and in robots whose distributed flexibili ty is limited for each link to the plane orthogonal to the associated motor axis. Experimental results are included to show the improved rat e of convergence of the proposed scheme applied to a two-link flexible robot available in our laboratory.