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.

A Novel Reconfigurable 3-DOF Parallel Kinematics Machine

Abstract

This paper proposes a novel, reconfigurable parallel kinematics machine with three degrees of freedom that can be used for various three-axis manipulation tasks, including machining. By locking some joints, the proposed parallel kinematics machine (PKM) can be transformed into four topologies with eight configurations to attain certain kinematic properties while keeping the number of its degrees of freedom unchanged. Either the proximal or intermediate prismatic joints of the reconfigurable PKM can be actuated. Some of the configurations are orthogonal configurations having a large rectangular cuboid workspace, and some other configurations are non-orthogonal configurations which provide the capability to perform a machining task to a large workpiece in various positions with respect to the machine. Accordingly, the proposed machine can be transformed from an orthogonal machine to a non-orthogonal machine with the advantages of each. The mobility of the various topologies of the reconfigurable PKM is rigorously analyzed using the screw theory. The workspace is analyzed using a graphical approach and verified by a computational approach. The pose kinematics shows that the various topologies have unified kinematics. The differential kinematics shows that the singularities in the various configurations occur at the workspace boundary. Similarly, the stiffness analysis shows that the low-stiffness postures occur around the workspace boundary. Accordingly, a used workspace far from the workspace boundary easily avoids the singularities and the low stiffness.

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