Latest Papers

ASME Journal of Mechanisms and Robotics

  • Ranking Static Balancing Methods Based on the Actuating Frictional Effort
    on April 17, 2025 at 12:00 am

    AbstractWhen a linkage is statically balanced, the effort required to actuate it quasi-statically in the absence of friction is zero. This is true irrespective of how the static balancing is accomplished. However, the effort is required to actuate the linkage when the Coulomb friction is present in the joints. This article shows that different static balancing methods lead to different magnitudes of the actuating frictional efforts. We further show that there exists a class of static balancing ways where between any two ways, one of the ways has a distinctively smaller magnitude of the actuating frictional effort for all values of the actuating kinematic variable. Hence, in such a case, the ways of static balancing can be ranked based on the magnitude of the actuating frictional effort. This has practical relevance when a statically balanced linkage has the Coulomb friction in its joints. Furthermore, we demonstrate that a smaller magnitude of the actuating frictional effort can be correlated to a smaller magnitude of the joint reaction forces. Thus, the magnitude of the actuating frictional effort can be used to assess the magnitude of the joint reaction forces irrespective of whether the friction in the joints is real or numerically simulated.

  • Instant Grasping Framework of Textured Objects Via Precise Point Matches and Normalized Target Poses
    on April 17, 2025 at 12:00 am

    AbstractTo reliably manipulate previously unknown objects in semi-structured environments, robots require rapid deployments and seamless transitions in pose estimation and grasping. This work proposes a novel two-stage robotic grasping method that instantly achieves accurate grasping without prior training. At the first stage, depth information and structured markers are utilized to construct compact templates for packaged targets, reducing noise and automating annotations. Then, we conduct coarse matching and design a new variant of the iterative closest point algorithm, named adaptive template-based RANSAC and iterative closest point (ATSAC-ICP), for precise point cloud registration. The method extracts locally well-registered pairs, regresses and optimizes six-degree-of-freedom (6-DOF) pose to satisfy confidence probability and precision threshold. The second stage normalizes the target pose for consistent grasp planning, which is based on scene and placement patterns. The proposed method is evaluated by several sets of experiments using various randomly selected textured objects. The results show that the pose errors are approximately ±2 mm, ±3 deg, and the successful grasping rate is over 90%. Physical experiments, conducted in different lighting conditions and with external disturbances, demonstrate effectiveness and applicability in grasping daily objects.

  • Improving Exoskeleton Brace Design: Alleviating Misalignment and Parasitic Forces
    on April 17, 2025 at 12:00 am

    AbstractThis article presents a design methodology for exoskeleton-user connection attachments, i.e., braces that aim to reduce parasitic forces and potentially improve user comfort. The proposed brace structure incorporates additional passive joints, identified through a hyperstaticity analysis to minimize undesired tangential forces, e.g., rubbing against the user’s skin. To assess the proposed structure, we primarily conducted simulation experiments using a human-exoskeleton coupled model in an MSC ADAMS environment. Subsequently, a series of real-life experiments was conducted using a self-balancing bipedal exoskeleton with two distinct dummy manikins. The results demonstrated the feasibility of the proposed brace structure in reducing the parasitic forces and slippage compared to the conventional fixation approach.

Design of a Four-Bar Latch Mechanism and a Shear-Based Rotary Viscous Damper for Single-Axis Prosthetic Knees

Abstract

With over 30 million people worldwide requiring assistive devices, there is a great need for low-cost and high-performance prosthetic technologies that can enable kinematics close to able-bodied gait. Low-income users of prosthetic knees in the developing world repeatedly report the need for n inconspicuous gait to mitigate the severe socioeconomic discrimination associated with disability. However, passive prosthetic knees designed for these users have primarily focused on stability and affordability, often at the cost of the high biomechanical performance that is required to replicate able-bodied kinematics. In this study, we present the design and preliminary testing of two distinct mechanism modules that are novel for passive prosthetic knee applications: the stability module and the damping module. These mechanisms are designed to enable users of single-axis, passive prosthetic knees to walk with close to able-bodied kinematics on level-ground, specifically during the transition from the stance phase to the swing phase of the gait cycle. The stability module was implemented with a latch mounted on a virtual axis of a four-bar linkage, which can be engaged during early stance for stability and disengaged during late stance to initiate knee flexion. The damping module was implemented with a concentric stack of stationary and rotating pairs of plates that shear thin films of high-viscosity silicone oil. The goal of the resulting first-order damping torque was to achieve smooth flexion of the prosthetic knee within the able-bodied gait range (64 ± 6 deg). For preliminary user-centric validation, a prototype prosthetic knee with the stability module and two different dampers (with varying damping coefficients) was tested on a single subject with above-knee amputation in India. The stability module enabled smooth transition from stance to swing with timely initiation of knee flexion. The dampers also performed satisfactorily, as the increase in the damping coefficient was found to decrease the peak knee flexion angle during swing. The applications of the mechanisms presented in this article could significantly improve the kinematic performance of low-cost, passive prosthetic knees.

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