Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

Redundancy of different types in the context of serial manipulators has reached a good level of maturity over the years. Most notably, kinematic redundancy (i.e., adding more joints and links than those strictly required by the task) for better kinematic performance or obstacle avoidance has been the focus of a number of works and successful manipulator designs (e.g., Canadarm). In parallel manipulators (PMs), however, redundancy is still in its infancy. Some recent works have used redundancy to tackle a few common issues of PMs (e.g., small and/or highly singular workspaces) and to develop new or improved manipulator architectures. The research proposed here will study actuation redundancy from theoretical and practical perspectives.

In terms of actuation redundancy, the focus will be on Cable Driven Parallel Manipulators (CDPMs) which have potentially large workspaces. Although it is possible to design CDPMs with very large workspaces (e.g., the SkyCam), the resulting CDPMs have a very large footprints as well. This is mostly due to the fact that cables can only pull and always need to be kept in tension. Here, it is proposed to enhance CDPMs with actuated coiled or telescopic struts that will essentially create manipulators with hybrid actuation. Since the new actuated members would permit both pushing and pulling, the region in space in which the manipulator can perform tasks can be extended quite significantly.

Efficiently determining the region in which a manipulator can apply or sustain a certain minimum force/moment couple is essential to determining the best manipulator for a specific task. New methods and efficient computational tools are required to perform this task fast enough to allow optimal design of manipulators. With these methods and tools, a robot designer would be able to determine the number, placement and characteristics of all the actuators (whether they are cables or coiled/telescopic struts) to perform the desired task.

An important part of the proposed work is the study and design of the actuators using either tape springs or novel elements such as slit tubes or bistable composite tubes. These light members can be deployed from a spool yet they can sustain axial forces in both directions. That is, they will allow forces to be applied both in tension and compression while having relatively long strokes. Although variants of this technology have existed for over two decades, they have been used on low speed applications such as deployable space structures. Here, the intention is to use the technology in relatively high speed applications. These actuators will greatly enhance the scope and allow new practical application of CDPMs.

Overall, this work will give robot designers better design tools for PMs and a larger selection of kinematic architectures. A very significant by-product of the work will be the development and design of extensible rods for high speed applications.