Intrinsic repeatability: A new index for repeatability characterisation

The paper deals with the question of robot precision and how to characterise repeatability. Hence ISO and ANSI repeatability indexes advantages and drawbacks are analysed. A new intrinsic repeatability index is proposed that can estimate the robot endpoint position variability satisfying the non-bias and convergence conditions. Computation of this index is performed using simulated straight and drifting trajectories. Influence of load on repeatability is studied using an experimental determination of an angular covariance matrix. Therefrom intrinsic repeatability can be computed in every workspace location using only this covariance matrix and the stochastic ellipsoid theory.