Latest Papers

ASME Journal of Mechanisms and Robotics

  • An Improved Dual Quaternion Dynamic Movement Primitives-Based Algorithm for Robot-Agnostic Learning and Execution of Throwing Tasks
    on May 9, 2025 at 12:00 am

    AbstractInspired by human nature, roboticists have conceived robots as tools meant to be flexible, capable of performing a wide variety of tasks. Learning from demonstration methods allow us to “teach” robots the way we would perform tasks, in a versatile and adaptive manner. Dynamic movement primitives (DMP) aims for learning complex behaviors in such a way, representing tasks as stable, well-understood dynamical systems. By modeling movements over the SE(3) group, modeled primitives can be generalized for any robotic manipulator capable of full end-effector 3D movement. In this article, we present a robot-agnostic formulation of discrete DMP based on the dual quaternion algebra, oriented to modeling throwing movements. We consider adapted initial and final poses and velocities, all computed from a projectile kinematic model and from the goal at which the projectile is aimed. Experimental demonstrations are carried out in both a simulated and a real environment. Results support the effectiveness of the improved method formulation.

  • Chained Timoshenko Beam Constraint Model With Applications in Large Deflection Analysis of Compliant Mechanism
    on May 9, 2025 at 12:00 am

    AbstractAccurately analyzing the large deformation behaviors of compliant mechanisms has always been a significant challenge in the design process. The classical Euler–Bernoulli beam theory serves as the primary theoretical basis for the large deformation analysis of compliant mechanisms. However, neglecting shear effects may reduce the accuracy of modeling compliant mechanisms. Inspired by the beam constraint model, this study takes a step further to develop a Timoshenko beam constraint model (TBCM) for initially curved beams to capture intermediate-range deflections under beam-end loading conditions. On this basis, the chained Timoshenko beam constraint model (CTBCM) is proposed for large deformation analysis and kinetostatic modeling of compliant mechanisms. The accuracy and feasibility of the proposed TBCM and CTBCM have been validated through modeling and analysis of curved beam mechanisms. Results indicate that TBCM and CTBCM are more accurate compared to the Euler beam constraint model (EBCM) and the chained Euler beam constraint model (CEBCM). Additionally, CTBCM has been found to offer computational advantages, as it requires fewer discrete elements to achieve convergence.

Cyclic Reconfigurability of Deployable Ring Structures With Angulated Beams

Abstract

Deployable ring structures have been useful concepts for engineering design applications due to their smooth transformation from an initially compact configuration to a substantially larger deployed state. As a result, over the past few decades, various computational and kinematic models have been introduced to analyze the behavior of such deployable structures. Here, we propose a type of deployable ring structure designed based on a transformable concept known as the Swivel Diaphragm. In particular, the geometry of the deployable ring structure is introduced, including different structural configurations with fixed pivots and angulated beams. Then, taking a group-theoretic approach, we establish appropriate constraint equations and perform a symmetry-adapted kinematic analysis. In the next step, the mobility and self-stress states of three example structures are studied, including a simple ring structure with C3 symmetry, a C6-symmetric ring with a hexagonal Swivel Diaphragm structure, and a general Cn-symmetric ring structure with inner hoops. The usefulness and effectiveness of the utilized group-theoretic approach are examined and validated through the study of these examples. We show that the kinematic behavior of the numerical models developed in this study agrees well with the finite element results obtained using abaqus. Importantly, the illustrated motion trajectories of the reconfigurable structures demonstrate that they retain a single degree-of-freedom as well as a cyclic symmetry. Moreover, it is shown that the angulated members necessarily rotate around the fixed pivots, which could be practically desirable in designing transformable structures for various applications in engineering and architecture.

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