Sensitivity Analysis of a Suspended CableDriven Parallel Robot to Design Parameters

Abstract

Cabledriven parallel robots (CDPRs) are system driven exclusively by cables, giving them advantages in operation. However, this also introduces complexity into their mechanical behavior. Indeed, the cable elasticity is affected by a hysteresis phenomenon. There is therefore an uncertainty about the actual value of the cable’s Young’s modulus. However, uncertainty analysis on design parameters of CDPR has not been conducted yet. So, this article first introduces a new modeling of CDPRs allowing to take in consideration the sagging of the cables while considering different pulley architectures as well as the cable dead length between the winch and the pulley. Then, a sensitivity analysis of the main design parameters on the positioning error of the moving platform (MP) is performed through a design of experiments conducted on a suspended CDPR with four cables. For this purpose, the variation of the Young’s modulus of the cables is determined. This allows to quantify and to rank the effects on the theoretical MP pose error of important design parameters that are the type of pulley joint, cable’ Young’s modulus, the cable mass, and the MP mass. This study is conducted for different sizes of CDPR. The results obtained show that the evolution of the effects of the design parameters is not the same depending on the size of the CDPR. Technical major considerations are derived from the presented results as guidelines for CDPR designer, keeping the modeling simple but robust enough for realtime control of CDPRs.