Vector analysis of the cable tension conditions

Abstract

The use of cable-driven robots is growing because of several important features, such as their structural simplicity and reduced mass and production cost compared to rigid-structure robots. However, the cable-driven mechanisms present some drawbacks, such as the fact that the cables are always tensioned to avoid errors of trajectory of the end-effector. In addition, if this necessary traction exceeds a maximum limit, cable breakage may occur. In this sense, it is proposed in this paper a way to evaluate the cable tension conditions in order to maintain the traction in each cable within an acceptable range, that assure the good operation of the robot. For this, a planar truss of rigid links with revolute joints is considered and one of the links is replaced by a cable. Then, the schematic representation of the system is made and it is modeled statically by the Davies method. In this way a homogeneous linear system is obtained that is solved from the null space of the coefficient matrix and then finally the tension in the cable can be evaluated.