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.

Connectivity Calculation-Based Automatic Synthesis of Planar Multi-Loop Mechanisms

Abstract

The creative design of kinematic structures with excellent performance remains an open issue in the quest for developing novel multi-loop mechanisms. This study presents an automatic method to synthesize all nonisomorphic planar multi-loop mechanisms satisfying the required connectivity between the base and the end-effector. First, based on the connectivity matrix calculation, all multi-loop mechanisms are generated from synthesized kinematic chains. Second, the concepts of perimeter, canonical, and characteristic graphs of multi-color topological graphs are addressed to acquire the simplified characteristic hybrid code (SCHC) in order to eliminate isomorphic multi-loop mechanisms. Then, an automatic method to synthesize all nonisomorphic planar multi-loop mechanisms with the required connectivity between the base and the end-effector is provided. Finally, a practical application of this synthesis method is illustrated by taking the mechanical arm of a face-shovel hydraulic excavator as an example to demonstrate the effectiveness of the method.
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