Inverse dynamics analysis of a 4-d.o.f. parallel robot H4

This paper addresses the inverse dynamics of a 4-d.o.f. parallel robot, H4. Simplified inverse dynamics models have been proposed so far in which the inertia of a rod is neglected. Computation of the inertia of the rod was a heavy load for past computers and, hence, the simplified inverse dynamics were useful for online computation. However, owing to the recent great progress in computer hardware, online computation of the full dynamics is no longer a heavy load for modern computers. Therefore, a detailed inverse dynamics model of H4 is proposed in this paper. The Newton-Euler method is adopted for generating inverse dynamics solutions for H4 which have four (S-S)₂ (two spherical-spherical) chains in each rod. In order to evaluate the proposed inverse dynamics model, three controllers are tested: (i) PD controller, (ii) PD controller with velocity feed-forward and (iii) dynamic compensation controller based on the proposed dynamics model. The experimental results are presented and analyzed. It is also shown that the simplified dynamics model can be used without clear deterioration of control quality.