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.

Analysis and Validation of a Flexible Limb/Cable Hybrid-Driven Parallel Continuum Manipulator

Abstract

Cable-driven parallel manipulators and parallel continuum manipulators have attracted increasing attention in pick-and-place manipulation, owing to their low inertia and high safety. In cable-driven parallel robots, cables are utilized to control a moving platform, whereas parallel continuum manipulators employ flexible limbs. By combing these two types of mechanisms, the authors propose a novel flexible limb/cable hybrid-driven parallel continuum manipulator (HDPCM). The flexible limbs, equipped with their ability to withstand pushing forces applied on the moving platform, are a critical component of the HDPCM. Meanwhile, the cables, with their proficiency to modulate the shape of the flexible limbs and endure some of the pulling force, reduce the possibility of large divergence in flexible limbs. This results in an improved reachable workspace and load capacity for the manipulator. To predict the configuration of the proposed manipulator, an efficient kinetostatics analysis is given, utilizing a discretization-based approach. Among the infinitely many solutions to the inverse problem, the configuration with minimal potential energy is selected as the optimal solution. Finally, a prototype is fabricated, and validation experiments are conducted, which demonstrate that the prototype exhibits acceptable positioning accuracy and passive compliance. Furthermore, the proposed manipulator is validated to possess relatively superior performance in the workspace and load capacity.

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