Design and Integration of a Novel Robotic Leg Mechanism for Dynamic Locomotion at High-Speeds

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Virginia Tech

Existing state-of-the-art legged robots often require complex mechanisms with multi-level controllers and computationally expensive algorithms. Part of this is owed to the multiple degrees of freedom (DOFs) these intricate mechanisms possess and the other is a result of the complex nature of dynamic legged locomotion. The underlying dynamics of this class of non-linear systems must be addressed in order to develop systems that perform natural human/animal-like locomotion. However, there are no stringent rules for the number of DOFs in a system; this is merely a matter of the locomotion requirements of the system. In general, most systems designed for dynamic locomotion consist of multiple actuators per leg to address the balance and locomotion tasks simultaneously. In contrast, this research hypothesizes the decoupling of locomotion and balance by omitting the DOFs whose primary purpose is dynamic disturbance rejection to enable a far simplified mechanical design for the legged system. This thesis presents a novel single DOF mechanism that is topologically arranged to execute a trajectory conducive to dynamic locomotive gaits. To simplify the problem of dynamic balancing, the mechanism is designed to be utilized in a quadrupedal platform in the future. The preliminary design, based upon heuristic link lengths, is presented and subjected to kinematic analysis to evaluate the resulting trajectory. To improve the result and to analyze the effect of key link lengths, sensitivity analysis is then performed. Further, a reference trajectory is established and a parametric optimization over the design space is performed to drive the system to an optimal configuration. The evolved design is identified as the Bio-Inspired One-DOF Leg for Trotting (BOLT). The dynamics of this closed kinematic chain mechanism is then simplified, resulting in a minimal order state space representation. A prototype of the robotic leg was integrated and mounted on a treadmill rig to perform various experiments. Finally, open loop running is implemented on the integrated prototype demonstrating the locomotive performance of BOLT.

Legged Locomotion, Mechanism and Design