Latest Papers

ASME Journal of Mechanisms and Robotics

  • Fully Foldable Mechanical Metamaterials With Isotropic Auxeticity and Its Generated Multi-Mode Folding Form
    on February 10, 2025 at 12:00 am

    AbstractAuxetic materials, a type of mechanical metamaterial with negative Poisson's ratio, are potentially utilized in the realms of energy absorption and engineering structures. However, most of the existing auxetic materials either contain a large amount of rotational motion or still have gaps when fully folded, which is not conducive to lifting loads. Besides, their application is limited to flexible environments due to their single-folding mode. To overcome such limitations, a fully foldable mechanical metamaterial with isotropic auxeticity is proposed by utilizing the Sarrus mechanism, and a derivative multi-mode folding form is obtained in this paper. Then, the degrees-of-freedom (DOF), bistability, and kinematic characterizations are analyzed to show the performance of the proposed structures. Finally, the parameters of the proposed fully foldable mechanical metamaterials are discussed to simplify the structures. Some prototypes are fabricated to validate the effectiveness and performance of the proposed mechanical metamaterials. The proposed mechanical metamaterials have some merits, such as isotropic auxeticity, being fully folded to achieve dense compression, being bistable with load-bearing capacity, multi-mode folding form, and single-DOF, and they have versatile potential applications in complex environments requiring large deformation and flexible adaptation.

  • Elastostatic Performance Evaluation of a Full-Mobility Parallel-Kinematics Machine With Flexible Links
    on February 10, 2025 at 12:00 am

    AbstractThe subject of this article is the elastostatics of a novel three-limb, full-mobility parallel-kinematics machine (PKM) with flexible links, intended for high-frequency, small-amplitude operations. The objective is to establish the Cartesian stiffness model and performance indices capable of guiding the structural design of the machines of interest. We base our analysis on what we term an elastostatic Cartesian model: the light-weight limb rods are modeled as identical, massless, linearly elastic beams; the motor shafts and couplings are modeled likewise, with the beams replaced by identical, massless, linearly elastic torsional springs, both link flexibility and actuator flexibility thus being considered. The moving platform is assumed to be the only moving rigid body of the machine. This platform is thus regarded as a rigid body elastically mounted onto the base platform via a six-degree-of-freedom (six-DoF) Cartesian spring. Then, the PKM 6×6 Cartesian stiffness matrix, considering the flexibility of both limb rods and motor shafts, is derived via the pertinent kinetostatic relations. Moreover, three alternative indices are defined from this model to evaluate the robot stiffness, which allows us to choose the most appropriate one for specific applications.

  • Announcing the Journal of Mechanisms and Robotics 2023 Best Paper Award
    on February 10, 2025 at 12:00 am

    JMR Best Paper for 2023

  • Active Cables Selection for Collocated Vibration Control of Small-Sized Overconstrained Cable-Driven Parallel Robots
    on February 10, 2025 at 12:00 am

    AbstractCable-driven parallel robots (CDPRs) are well appreciated for high dynamics applications, due to their lightweights moving parts. Nevertheless, due to the low stiffness of cables, vibrations can occur and can degrade performances if high precision is required, such as in additive manufacturing for instance. Previous works have studied techniques to counteract vibrations, like using motor command or embedded devices. Based on a previous first exploration of using piezoelectric transducers on cables for this type of robot, this paper presents a proper formulation of the collocated active vibration control to damp the end-effector oscillations of small-sized overconstrained CDPRs by the measure of the variation in cable tensions. This goes through a modeling of such a robot with embedded piezoelectric transducers under appropriate assumptions. From this control formulation, it is shown that the collocated nature of these transducers are fundamental. It is thus possible to highlight an energetic index of active cables selection, regardless of the used control law. The proposed technique is developed theoretically and analyzed through simulations on an eight-cable robot.

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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