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.

Performance Analysis and Optimal Design of a Novel Schöenflies-Motion Asymmetric Parallel Mechanism

Abstract

Since previous studies of parallel mechanisms (PMs) have tended to favor symmetrical overall configuration to obtain relatively stable kinematic and dynamic performance and to satisfy isotropic requirements. The analysis of kinematic and dynamic performance of asymmetric mechanisms has been an issue of interest. In this paper, an asymmetric SCARA-type PM with four-degrees-of-freedom (DOF) is proposed. First, the orientation characteristic set is calculated to obtain the DOF of the PM. Then, the inverse kinematics and the velocity and acceleration of each branch chain of the mechanism are analyzed. The dynamic model of the mechanism is established according to the principle of virtual work. The workspace of the mechanism is drawn according to the constraints that have been given to the mechanism’s kinematic pairs. The singularity, dexterity, motion/force transfer performance, and maximum acceleration performance of the mechanism are also analyzed. On this basis, the kinematic and dynamic performance evaluation indexes of the mechanism are studied. Finally, the workspace and acceleration performance of the mechanism are optimized based on the differential evolution (DE) algorithm to obtain the structural parameters when the mechanism achieves optimal performance. The asymmetric PM proposed in this paper, as well as the algorithm of performance index and optimization method used, can provide some reference value for configuration design and optimization analysis.

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