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.

Variable Degree-of-Freedom Spatial Mechanisms Composed of Four Circular Translation Joints

Abstract

This paper deals with the construction and reconfiguration analysis of a spatial mechanism composed of four circular translation (G) joints. Two links connected by a G joint, which can be in different forms such as a planar parallelogram, translate along a circular trajectory with respect to each other. A spatial 4G mechanism, which is composed of four G joints, usually has one degree-of-freedom (DOF). First, a 2-DOF spatial 4G mechanism is constructed. Then, a novel variable-DOF spatial 4G mechanism is constructed starting from the 2-DOF 4G mechanism using the approach based on screw theory. Finally, the reconfiguration analysis is carried out in the configuration space using dual quaternions and tools from algebraic geometry. The analysis shows that the variable-DOF spatial 4G mechanism has one 2-DOF motion mode and one to two 1-DOF motion modes and reveals how the 4G mechanism can switch among these motion modes. By removing one link from two adjacent G joints each and two links from each of the remaining two G joints, we can obtain a queer-rectangle and a queer-parallelogram, which are the generalization of the queer-square or derivative queer-square in the literature. The approach in this paper can be extended to the analysis of other types of coupled mechanisms using cables and gears and multi-mode spatial mechanisms involving G joints.
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