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.

Rigid-Foldable Mechanism Inspired by Origami Twisted Tower

Abstract

Rigid origami mechanisms have great practical utility in different fields. This paper presents a rigid and foldable mechanism based on the origami artwork Twisted Tower. The mathematical model of the funnel-shaped tower cell was developed for the first time, which accurately describes its kinematic behavior. Based on this model, criteria for the appropriate geometry of the tower components are proposed to prevent internal interference in the tower mechanism during the twisting movement. In this paper, two geometric design cases of twisted tower mechanisms, including a normal-shaped tower and a heteromorphic tower, are presented. Several additional modifications were also imposed to adapt the proposed mechanism to generalized and standardized manufacturing and assembly. Experimental results illustrate that the kinematic characteristics of the fabricated mechanism meet its designed performance. Furthermore, the proposed mechanism is suitable for applications such as continuum manipulators, which exhibit much better resistance to external loads than their flexible-rigid hybrid counterparts.

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