Parameter identification of a semi-flexible kinematic model for serial manipulators.

Structural and control flexibilities affect the absolute precision of serial manipulators. A semi-flexible kinematic model is developed, to improve the absolute static precision. It expands the solid body model by incorporating a spring effect for each joint and a beam effect for each link. The identifiability of the added parameters and the effect of measurement noise are explored on a R4 robot. It requires efforts and pose errors to be known in the tool frame only. Simulation results show that identification of some of the parameters is sensitive to measurement noise on forces and pose. In fact, joint flexibility displacement and beam flexion that occur in the same plane are difficult to dissociate in noisy condition. However, a subset of the original parameters can be defined leading to a model that can be more accurately identified when measurement noise is present. In simulation, precompensation is used in an inverse semi-flexible model that results in a 98% decrease of pose error compared to the rigid body inverse geometric model.