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.

Constraint-Based Analysis of Parallel Kinematic Articulated Wrist Mechanisms

Abstract

This paper presents a systematic constraint-based analysis of the performance attributes of eight parallel kinematic articulated wrist mechanisms from the existing literature. These performance attributes include the number, nature (i.e., pure rotation, or translation, or a combination), and location of a mechanism’s Degrees of Freedom (DoFs) in the nominal and displaced configurations, load transmission capability along these DoFs, and load-bearing capability along the constraint directions. This systematic analysis reveals performance tradeoffs between these performance attributes for a given mechanism as well as design tradeoffs across these mechanisms. This analysis also helps inform the suitability of a given mechanism for specific applications.
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