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.

Folding Process Planning of Rigid Origami Using the Explicit Expression and Rapidly Exploring Random Tree Method


In this study, we propose a novel method for planning the folding process of a rigid origami mechanism, i.e., we explore the intermediate process of the mechanism from an initial state to a target state without self-intersection via a path-finding algorithm. A typical problem associated with a path-finding algorithm is that a feasible configuration space of rigid origami is a lower-dimensional subset of the entire parameter space. When all the folding angles are considered as free parameters to plan the folding process, it is generally not possible to obtain a feasible configuration via sampling. In this study, the parameters corresponding to the degree-of-freedom (DOF) are used as independent variables, and the remaining fold angles are considered as dependent variables that can be calculated via the explicit expression method (EEM). First, we explain the method for choosing the parameters related to DOF to represent the configuration of the origami mechanism. Then, we show the procedure for selecting a valid configuration from many possible configurations computed via EEM. For this purpose, we introduce criteria for each vertex to determine whether the two configurations can be continuously connected. Next, the method for planning the folding process of rigid origami is introduced via the rapidly exploring random tree (RRT) method. Finally, we implemented the folding process simulation platform and applied it to different patterns. The results of the experiments are presented.
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