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 Novel Tunable Stiffness Mechanism Using Filament Jamming


The jamming mechanism is a crucial method to tune the stiffness of soft-bodied machines to adapt to their surroundings. However, it is difficult for the present jamming structures to integrate them into systems with complicated shapes such as twist, cylinder, and spiral. This paper introduces a novel jamming mechanism termed a filament jamming technique, which varies stiffness using jamming of a cluster of tiny and compliant filaments. The jamming structure demonstrated various characteristics such as softness, shape compatibility, lightweight, and high stiffness. These feats can meet a variety of application scenarios that the traditional jamming one cannot afford. The experimental test was used to explore the jamming structure’s stiffness behavior and dynamic performance. The influence of the filament structure dimensions, material properties, and the vacuum pressure on the stiffness was revealed. With the negative pressure increasing, both the natural frequency and damping ratio increase due to the rigidity variation. It indicates that the filament jamming structure has excellent response rapidity and shock resistance. Our work demonstrated some versatile features of the filament jamming technology, like shape adaptation, shape-preserving, stiffness stability, and compliance. To demonstrate the advantage of the jamming technique, we constructed a soft gripper and a torsional actuator to illustrate how the mechanics of filament jamming can enhance real-world robotics systems’ performance. Therefore, the filament jamming mechanism provides various machines and structures with additional properties to increase forces transmitted to the environment and tune response and damping. This study aims to foster a new generation of mechanically versatile machines and structures with softness and stiffness.

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