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 Responses of Origami-Inspired Structures Connected by Groove Compliant Joints

Abstract

The compliant mechanism can effectively reduce friction and eliminate the joint gap during the motion. The performances of compliant joints directly determine the overall behavior of mechanisms. In this paper, a new type of compliant joint is designed based on weakened creases and elastic–plastic materials. Parametric analysis is carried out to investigate the influence of compliant joint details on its structural performances by combining finite element methods and experiments. The compliant joints are evaluated and optimized regarding the rotational stiffness and plastic strain magnitude of the slot region. In addition, the optimized compliant joint is introduced to the Miura unit. The configuration analysis is performed for the folding, unfolding, and releasing processes, which are further extended to the discussion on the cyclic performance of the compliant joint. It can be found that the origami-inspired structures can maintain a high residual stiffness after the release process. Finally, the methodology is applied to the Miura origami array embedded with the designed compliant joint. The results of dimensional errors and stress distributions can show that the design of the compliant joints can effectively control the configuration of the Miura origami array. The principle in this paper can open a new avenue to design and utilize the compliant in the deployable or morphing structures.

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