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.

Mobility and Kinematic Bifurcation Analysis of Origami Plate Structures


Bifurcation behavior analysis is the key part of mobility in the application of origami-inspired deployable structures because it opens up more allosteric possibilities but leads to control difficulties. A novel tracking method for bifurcation paths is proposed based on the Jacobian matrix equations of the constraint system and its Taylor expansion equations. A Jacobian matrix equation is built based on the length, boundary, rigid plate conditions, and rotational symmetry conditions of the origami plate structures to determine the degrees-of-freedom and bifurcation points of structural motion. The high-order expansion form of the length constraint conditions is introduced to calculate the bifurcation directions. The two kinds of single-vertex four-crease patterns are adopted to verify the proposed method first. And then, the motion bifurcations of three wrapping folds are investigated and compared. The results demonstrate the rich kinematic properties of the wrap folding pattern, corresponding to different assignments of mountain and valley creases. The findings provide a numerical discrimination approach for the singularity of rigid origami structure motion trajectories, which may be used for a wide range of complicated origami plate structures.

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