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 Reconfigurable 6 R Linkage With Six Motion Modes and Three Topological Structures

Abstract

In this paper, a new reconfigurable 6R linkage is obtained by combining two identical equilateral Bennett linkages arranged in a plane-symmetric manner, and a detailed kinematic analysis is conducted which shows that there are six distinct motion modes and three topological structures of the derived mechanism without changing the types of kinematic joints. Explicit relationships among the kinematic variables are obtained with D–H method and various modes are discussed in detail. Bifurcation points are derived and the reconfigurations are analyzed. The result shows that the mechanism has six motion modes which contain a special case of a plane-symmetric 6R mode and a special case of a two-fold symmetric 6R mode, an X-shaped motion mode, and two V-shaped motion modes. A physical prototype is fabricated to verify the derivation and it shows that the mechanism can transform among all the motion modes without the need of reassembling.

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