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.

Inertial Measurement Unit-Based Optimization Control of a Soft Exosuit for Hip Extension and Flexion Assistance

Abstract

The optimization of the assistive force of a soft exosuit is crucial to the assistive effect. In this paper, an inertial measurement unit (IMU)-based optimization controller was designed to provide effective hip extension and flexion assistance for a soft hip-assistive exosuit. The parameters of the assistive profiles that were defined by two functions were approximatively estimated based on an analysis of biological hip power, and then optimized in real time using the hip angles measured by two IMUs bound to the thighs of the wearer. The peak and offset timings were determined using the parameters of the previous gait, while the start and stop points were determined from those of the current gait. Confirmation experiment was conducted in which four subjects were tested to demonstrate the validity of the optimization by applying the optimized parameters to the soft exosuit developed by the authors’ group. Two of the subjects completed the outdoor walking test at a self-determined pace while carrying a load of 15 kg. All the subjects conducted the walking test on a treadmill at a constant speed of 1.53 m/s with the same load. The results showed that the proposed optimization controller worked well without considering individual differences. In the outdoor walking test, the wearer’s natural gait could be maintained by applying the optimized assistive forces. In the treadmill walking test, metabolic rate with assistance turned on was reduced by 8.53 ± 2.65% (average ± SEM) compared with the result of assistance turned off.
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