Latest Papers

ASME Journal of Mechanisms and Robotics

  • Stable Inverse Dynamics for Feedforward Control of Nonminimum-Phase Underactuated Systems
    on January 25, 2023 at 12:00 am

    AbstractAn enhanced inverse dynamics approach is here presented for feedforward control of underactuated multibody systems, such as mechanisms or robots where the number of independent actuators is smaller than the number of degrees of freedom. The method exploits the concept of partitioning the independent coordinates into actuated and unactuated ones (through a QR-decomposition) and of linearly combined output, to obtain the internal dynamics of the nonminimum-phase system and then to stabilize it through proper output redefinition. Then, the exact algebraic model of the actuated sub-system is inverted, leading to the desired control forces with just minor approximations and no need for pre-actuation. The effectiveness of the proposed approach is assessed by three numerical test cases, by comparing it with some meaningful benchmarks taken from the literature. Finally, experimental verification through an underactuated robotic arm with two degrees of freedom is performed.

A Rigid Morphing Mechanism Enabled Earthworm-Like Crawling Robot

Abstract

Inspired by natural earthworms’ locomotion mechanism, this paper investigates how the earthworm’s muscle works and presents the approach to mimic segmental muscle by employing rigid elements-based morphing structures. Specifically, the proposed earthworm-like robot employs a class of 2D rigid elements and their array to achieve programable bidirectional 3D deformation, making the formed mechanism precisely controllable and work effectively, thus facilitating the robot’s peristaltic locomotion more efficient. To comprehensively investigate the morphing structure and its formed earthworm-like robot, the kinematics, mechanics, deformation-dependent locomotion framework with its adapted model, as well as the factors that affect the optimal velocity are developed and presented. Extensive simulations and experiments on the proposed robot are performed. The results verify the effectiveness of the morphing mechanism and it enabled earthworm-like robot and the consistency between the proposed locomotion model and the practical tests. The results also prove that regardless of the condition of the contact surface, the optimal phase shift angle can be achieved when each segment approximately contracts and relaxes once in one wavelength period. Our developed prototype achieves a speed of multiple body lengths per minute, which is very competitive compared with most developed earthworm-like robots.

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