Variable-Structure Cable-Driven Parallel Robots
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Date
2022-05-16
Authors
Rushton, Mitchell
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Cable-driven parallel robots (CDPR) are a special class of robotic manipulators consisting of a rigid end effector suspended, constrained, and actuated by a number of length-varying cables. Since cable mass is typically negligible, it allows CDPRs to be built with extremely low-inertia, enabling high-accelerations and the ability to span distances that would otherwise be impossible using rigid structures. Where CDPRs suffer is their inability to perform in cluttered installation spaces due to the need to avoid collisions between cables and the environment. This thesis proposes a design alternative defined as `variable-structure CDPRs' (VSCR) to address the inherent limitations CDPRs have regarding their limited usable workspaces in cluttered environments. What makes VSCRs unique is their ability to instantaneously alter their dynamic structure through collisions between cables and objects fixed in the environment. It is shown that, unlike traditional CDPRs, VSCRs are able to produce non-convex reachable workspaces: a property that is especially useful for circumventing obstacles and has implications for a wide range of applications such as rehabilitation, agriculture, and warehousing. An extended cable model for representing collidable cables is developed along with a corresponding inverse kinematics method as a foundation for initiating the study of VSCRs. Next, an atlas-based approach for representing VSCR configuration spaces is introduced, along with a method for its computation. The proposed representation, referred to as the `structure atlas,' is shown to be a powerful tool for performing VSCR workspace analysis and inverse kinematics. Finally, an experimental testbed is constructed and used for conducting several experimental studies to validate the previously mentioned theoretical contributions and observe the real-world capabilities of VSCRs. Mathematically and experimentally, it is shown that VSCRs dramatically improve the reachability and accessible workspaces CDPRs can achieve in cluttered or irregular environments.
Description
Keywords
collision avoidance, cable-driven parallel robots, variable-structure, robotics, kinematics