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.

An Improved Static Model for Bidirectional Notched Continuum Robot Considering the Cable Tension Loss

Abstract

The notched continuum mechanism is particularly suitable for natural orifice transluminal surgery benefiting from its small size and hollow structure. However, the widely used kinematic model based on constant curvature assumption does not reveal the actual deformation of the continuum mechanism, and its control accuracy is unstable, while the general mechanics model has the problem that the tension of the distal driving cable is difficult to measure. In this paper, a nonconstant curvature static model for a bidirectional V-shaped notched continuum mechanism is presented. The deformation of each part of the continuum mechanism from the distal end to the proximal end is analyzed in turn. The tension loss of the driving cable caused by the contact with the continuum mechanism is modeled using the capstan equation. The recursive equation between the deformation of each part of the continuum mechanism from the proximal end is derived, which can be solved numerically. The bending state of the continuum mechanism can then be estimated when only the tension of the proximal flexible cable is known. The model is experimentally verified by driving the continuum mechanism to move at a very low speed. The experiment results show that the estimation effect of the proposed model is significantly improved compared with that of the constant curvature model.

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