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.

Self-Aligning Rotational Latching Mechanisms: Optimal Geometry for Mechanical Robustness

Abstract

In concurrent work, we introduced a novel robotic package delivery system latching intelligent modular mobility system (LIMMS). Each LIMMS end effector requires a small, lightweight latching mechanism for pre-manufactured containers, such as cardboard boxes. In order to effectively process a high volume of packages, aligning the latching mechanism quickly and reliably is critical. Instead of depending on highly accurate controllers for alignment, we propose a novel self-aligning rotational mechanism to increase the system’s tolerance to misalignment. The radial latching design consists of evenly spaced blades that rotate into slots cut into the box. When misaligned, the blades contact the edges of the engagement slots, generating a self-correcting force that passively centers the blades with the slot pattern. This paper introduces a mathematical framework with closed form expressions to quantify error tolerance for these mechanisms. Through our mathematical and optimization analyses, it is shown that a two-blade design can tolerate a maximum misalignment of three times the radius to the blade tips, much larger than commonly used designs with three or more blade-like contacts. Our approach can be generalized for a class of rotational latching mechanisms with any number of blades. Utilizing this theory, a design process is laid out for developing an optimal self-aligning rotational latching mechanism given desired parameters and task constraints. With this methodology, we designed, manufactured, and verified the effectiveness of both two-blade and three-blade self-aligning in practical experiments.

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