Study of cable robots for hardware-in-the-loop contact dynamics simulation.

摘要

With the increasing interest and efforts for planetary exploration, space missions requiring physical contact are becoming more common than ever. Ground-based verification of contact dynamics of spacecraft in microgravity condition is extremely difficult. Using robotics technology, hardware-in-the-loop (HIL) contact dynamics simulation has demonstrated advantages over traditional technologies. However, the dynamics models of the rigid-link robots exclusively used in the current HIL simulators are so complicated that their own dynamics cannot be accurately predicted and compensated, which, in turn, significantly reduces the fidelity of these HIL simulators. To overcome this technical difficulty, this research proposed a new concept of using cable robots for HIL contact dynamics simulation. Unlike rigid-link robots, cable robots have much simpler dynamics models that can be predicted and compensated precisely and hence, they are more suitable for HIL simulators.;To verify the feasibility of this new concept, several fundamental technical problems associated with cable robots are investigated. (1) Force-closure: since cables can work in tension only, a cable robot may not have a force-closure at a given pose. A method of checking force-closure status for general 6-DOF cable robots with seven or more cables is proposed and mathematically proven based on convex analysis. (2) Workspace: One of the essential tasks of robot design is to ensure the required workspace. Force-closure workspaces of various cable robots are determined and their geometric features are discussed. (3) Vibration: cable robots bear a larger concern of vibration since cables are more flexible than rigid links. Based on natural frequency analysis, it is shown that cable robots can be stiff enough for the intended application and lateral vibration of cables has negligible effect on the overall vibration of cable robots. (4) Singularity: Due to the unidirectional constraint of cables, Jacobian-matrix based singularity analysis is not enough for cable robots. The singularities of general cable robots are newly classified and discussed.;The study results support the feasibility of using cable robots for HIL contact dynamics simulation. Additionally, as a spin-off application of cable robots, a cable-robot based active suspension system for neural rehabilitation is also investigated.