This paper is dedicated to the geometry selection of a redundantly actuated cable-suspended parallel robot intended to manipulate heavy payloads over a wide workspace. Cable-suspended refers here to cable-driven parallel robots in a crane-like setting, where all the cable drawing points are located on top of the base frame, gravity being used to keep the cables taut. Geometry selection consists of determining the relative positions of the cable drawing points on the base frame and of the cable attachment points on the mobile platform together with the cable arrangement between these two sets of points. An original performance index is introduced. It is defined as the maximum acceptable distance between the mobile platform geometric center and the center of mass of the set consisting of the platform and a payload. This performance index is of particular interest in heavy payload handling applications. Used within a two-phase geometry selection strategy, it yields a new cable-suspended robot geometry having a very large workspace to footprint ratio and able to handle heavy payloads. A large-dimension redundantly actuated cable-suspended robot was built in order to demonstrate these capabilities.

This paper introduces a new simplified static analysis of parallel robots driven by inextensible cables of non-negligible mass. It is based on a known hefty cable static modeling which seems to have been overlooked in previous works on parallel cable-driven robots. This cable modeling is obtained from a well-known sagging cable modeling, known as the catenary, by assuming that cable sag is relatively small. The use of the catenary has been shown to lead to a non-linear set of equations describing the kinetostatic behavior of parallel robots driven by cables of non-negligible mass. On the contrary, the proposed simplified static analysis yields a linear relationship between (components of) the forces in the cables and the external wrench applied to the robot mobile platform. As a consequence, by means of the simplified static analysis, useful wrench-based analysis and design techniques devised for parallel robots driven by massless cables can now be extended to cases in which cable mass is to be accounted for.

Generally, the cables of a parallel cable-driven robot are considered to be massless and inextensible. These two characteristics cannot be neglected anymore for large dimension mechanisms in order to obtain good positioning accuracy. A well-known model which describes the profile of a cable under the action of its own weight allows us to take mass and elasticity into account. When designing a robot, and choosing actuator and cable characteristics, a calculation of maximal tension has to be done. However, because cable mass has a significant effect on cable tensions, a model including cable mass has to be included in the design step. This paper proposes two methods to determine the appropriate cable and hence the maximal tensions in the cables. Applied to a large dimension robot, taking cable mass into account is proved to be necessary in comparison with an equivalent method based on the massless cable modeling. In this paper, only moving platform static equilibria are considered (slow enough motions).

Cable-driven robots are currently extensively studied. Generally, for this type of manipulators, cables are considered to be massless and inextensible. But for large working volume applications, their mass cannot be neglected. Based on a well-known model which describes the profile of a cable under the action of its own weight, the inverse and forward kinematics of minimally constrained cable-driven manipulators can be numerically computed. This paper studies the effects of taking cable mass into account by comparison to classical massless cable model. It highlights the real effects of such a model on cable lengths to reach a given position. The effects on cable tensions are also studied.