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.

Dexterity Analysis Based on Jacobian and Performance Optimization for Multi-Segment Continuum Robots

Abstract

This paper focuses on the performance analysis of multi-segment continuum robots, including reachable workspace and dexterity performance. Since excellent dexterity is an important feature of continuum robots, two local indices inspired by separating robotic Jacobian matrix, namely axiality and angularity dexterity, are introduced to explore the dexterity. Then, a Monte Carlo Method is adopted to simulate the distribution of local dexterity over the workspace. On this basis, the corresponding global indices in axiality and angularity are defined to assess global dexterity performance. To investigate the optimal kinematic performance, an objective function related to the segment lengths is designed under the consideration of reachable workspace and dexterity performance. Finally, Particle Swarm Optimization (PSO) algorithm is used to solve this optimization problem successfully. The optimal length distributions for two-segment and three-segment continuum robots are discovered. Most importantly, it is found that our method can also apply to general multi-segment continuum robots.
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