Increase of position accuracy for cable-driven parallel robots using a model for elongation of plastic fiber ropes

This paper investigates the modeling of elongation in plastic fiber ropes for cable-driven parallel robots. The aim is to increase the accuracy of such a machine by incorporating a simple model for cable elongation when a force is applied. Several other modeling techniques already exist which take into account pulleys, cable mass, and the cables' Young's modulus. Their calculation is involved and accuracy improvements are yet to be verified completely. Here, a simpler model which only takes into account a theoretical force, based on robot geometry, at a given pose and measured elongation coefficients is proposed. It is implemented and verified experimentally, on the fully constrained IPAnema 3 prototype. It is shown to give an accuracy improvement of two fifths, from 46.5 mm to 29.0 mm average position deviation.