Accuracy of large-scale cable-driven parallel robot with universal joint pulleys
Résumé
Additive Manufacturing (AM) for building construction is booming because it is a cost-saving method. However, the means currently used do not offer a lot of flexibility. In order to adapt to different building geometries, the mechanical architecture that drives the printhead must be able to adapt easily to its environment. Cable-Driven Parallel Robots (CDPRs) might be an alternative to offer this adaptability to large-scale AM. In this context, the general aim is to develop a CDPR architecture for large-scale AM applications. CDPRs are not accurate because the use of cables makes the architecture less rigid. Taking into account the cable deformation can reduce this inaccuracy. However, the variation in Young's moduli of the cables due to hysteresis loop is very difficult to quantify in real time. In addition, the use of CDPRs for large-scale applications can generate large forces in the pulleys. The CDPR studied in this paper is designed with universal joint pulleys that minimize internal stresses. This paper deals with the accuracy of large-scale CDPR taking into account universal joint pulleys, the total deformation of the cables and the uncertainty on their Young's moduli. The aim is to theoretically validate the use of CDPRs for housing AM. First, the full geometrico-catenary model of CDPR is presented. Secondly, the detailed mechanical design of the universal joint pulley is performed. Then, a stress analysis validates the use of the universal joint pulley. Finally, an analysis of the accuracy of the printhead shows that in some areas of the accessible static workspace, a CDPR can be used for large-scale AM.
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