Stiffness Analysis of Parallel Manipulators with Preloaded Passive Joints

TL;DR

This paper introduces a methodology for analyzing and improving the stiffness of parallel manipulators with preloaded passive joints, accounting for external loads and nonlinear load-deflection behavior, enhancing control accuracy.

Contribution

It develops a novel stiffness analysis method that includes preloading effects and external loads, and proposes a kinetostatic control algorithm for better accuracy.

Findings

Preloading eliminates buckling in the Orthoglide manipulator.

The methodology accurately predicts load-deflection relations.

Preloading improves stiffness near kinematic singularities.

Abstract

The paper presents a methodology for the enhanced stiffness analysis of parallel manipulators with internal preloading in passive joints. It also takes into account influence of the external loading and allows computing both the non-linear "load-deflection" relation and the stiffness matrices for any given location of the end-platform or actuating drives. Using this methodology, it is proposed the kinetostatic control algorithm that allows to improve accuracy of the classical kinematic control and to compensate position errors caused by elastic deformations in links/joints due to the external/internal loading. The results are illustrated by an example that deals with a parallel manipulator of the Orthoglide family where the internal preloading allows to eliminate the undesired buckling phenomena and to improve the stiffness in the neighborhood of its kinematic singularities.