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.

Cable Behavior Influence on Cable-Driven Parallel Robots Vibrations: Experimental Characterization and Simulation

Abstract

In this paper, the influence of cable behavior on cable-driven parallel robot (CDPR) is studied. This study is conducted with the goal of designing a medium size CDPR for additive manufacturing. This robot needs to have a high level of rigidity to guarantee a given tracking tool path error. First, the characterization of different thin cables (steel, Dyneema®, aramid) is presented. The mechanical properties of these cables, in terms of stiffness, damping, hysteresis, and creep are compared with regard to additive manufacturing applications. A stiffness model, which takes into account the cable preload, and a dynamic model of CDPR are proposed. The simulations of these two models are compared with experimental results obtained for the range of cables studied using dynamic stiffness analysis on an 8-cable fully constrained CDPR. This paper concludes on the type of cable that should be chosen for our application.
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