Tensegrity mechanisms using linear springs as tensioned elements constitute an interesting class of mechanisms. When considered as manipulators, their workspace remains however to be defined in a generic way. In this article, we introduce a workspace definition and at the same time a computation method, based on the estimation of the workspace boundaries. The method is implemented using a continuation method. As an example, the workspace assessment of a two degrees of freedom (DOF) planar tensegrity mechanism is presented.
International audienceCable-driven tensegrity mechanisms are now considered for various applications in which their reconfiguration capacities are required together with their inherent lightness. Moreover, they can exhibit interesting variable stiffness capacities through the modification of their level of prestress when composed of deformable cables. Control schemes that deal with both reconfiguration and stiffness variation have however not been developed in the literature yet.This paper presents two control strategies for that purpose to transform a cable-driven tensegrity mechanism into a variable stiffness device. The mechanism is a planar tensegrity mechanism allowing us to control an angular position and the associated stiffness. Relying on the properties of the mechanism models, the proposed control strategies allow a modulation of the stiffness or of its first time derivative. The interest of both propositions is outlined and an experimental investigation of their characteristics is performed. Encouraging results are obtained in terms of reconfiguration capabilities and stiffness variation
In this paper, the design of a new variable stiffness spherical joint for MR-compatible robotics is presented. It is based on the use of prestressed cable-driven mechanisms in singular configurations to provide large stiffness variation ranges, including zero stiffness configuration as required by the medical context. An original implementation is proposed, with a prestress adjustment system using pneumatic energy and taking advantage of multimaterial additive manufacturing. The proposed component combines compactness, MR-compatibility and is lightweight. The system is evaluated on a dedicated experimental setup with validation of the expected behavior, with in particular a very large achievable range of stiffnesses. The approach is effective for the design of such device and constitutes a novel solution for the design of variable stiffness devices with complex motions.
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