Latest Papers

ASME Journal of Mechanisms and Robotics

  • Theoretical Analysis of Workspace of a Hybrid Offset Joint
    on December 19, 2024 at 12:00 am

    AbstractOffset joints are widely used in robotics, and literature has demonstrated that axial offset joints can expand the workspace. However, the hybrid offset joint, which incorporates offsets in three orthogonal directions (x, y, and z axes), provides a more flexible and comprehensive range of motion compared to traditional axial offset joints. Therefore, a comprehensive understanding of the workspace of hybrid offset joints with three-directional offsets is essential. First, through a parameter model, the interference motion of hybrid offset joints is studied, considering three different directional offsets and obtaining analytical expressions. Next, based on coordinate transformations, the workspace of this joint is investigated, resulting in corresponding theoretical formulas. In addition, the influence of offset amounts in various directions on the joint’s workspace is examined. Finally, the application of hybrid offset joints in parallel manipulators (PMs) is introduced, highlighting their practical engineering value. Through comparative analysis, it is found that lateral offsets on the x- and y-axes adjust the maximum rotation angles, while the z-axis offset expands the rotational range of these joints. Moreover, by increasing the limit rotation angle of the passive joint in a specific direction, the application of hybrid offset joints in PMs can impact the workspace. These findings offer valuable insights for the design of hybrid offset joints and their applications in robotics.

  • A Novel Delta-Like Parallel Robot With Three Translations and Two Pitch Rotations for Peg-in-Hole Assembly
    on December 19, 2024 at 12:00 am

    AbstractThis paper presents a novel 5-degree-of-freedom (5-DOF) delta-like parallel robot named the double-pitch-delta robot, which can output three translations and two pitch rotations for peg-in-hole assembly. First, the kinematic mechanism of the new robot is designed based on the DOF requirements. Second, the closed-form kinematic model of the double-pitch-delta robot is established. Finally, the workspace of the double-pitch-delta robot is quantitatively analyzed, and a physical prototype of the new robot is developed to verify the effectiveness of the designed mechanism and the established models. Compared with the existing 5-DOF parallel robots with two pitch rotations, the double-pitch-delta robot has a simpler forward displacement model, larger workspace, and fewer singular loci. The double-pitch-delta robot can be also extended as a 6-DOF hybrid robot with the full-cycle tool-axis rotation to satisfy more complex operations. With these benefits, the new robot has a promising prospect in assembly applications.

Classification of 3-Degree-of-Freedom 3-UPU Translational Parallel Mechanisms Based on Constraint Singularity Loci Using Gröbner Cover

Abstract

A 3-degree-of-freedom (DOF) 3-UPU translational parallel mechanism (TPM) is one of the typical TPMs. Despite comprehensive studies on 3-UPU TPMs in which the joint axes on the base and the moving platform are coplanar, only a few 3-UPU TPMs with skewed base and moving platform have been proposed, and the impact of link parameters on constraint singularity loci of such TPMs has not been systematically investigated. The advances in computing comprehensive Gröbner system (CGS) or Gröbner cover of parametric polynomial systems provide an efficient tool for solving this problem. This paper presents a systematic classification of 3-UPU TPMs with skewed base and moving platform based on constraint singularity loci. First, the constraint singularity equation of a 3-UPU TPM is derived. Using Gröbner cover, the 3-UPU TPMs are classified into 12 types. Finally, a novel 3-UPU TPM is proposed. Reconfiguration analysis shows that unlike most existing 3-UPU TPMs which can transit from a 3-DOF translational mode to two or more 3-DOF operation modes, the proposed 3-UPU TPM can only transit from a 3-DOF translational mode to one general 3-DOF operation mode. The singularity locus divides the workspace of this 3-UPU TPM into two constraint singularity-free regions. As a by-product, a 3-UPU parallel mechanism that the moving platform can undergo 3-DOF translation and 1-DOF infinitesimal rotation is revealed. This work provides a solid foundation for the design of 3-UPU TPMs and a starting point for the classification of 3-UPU parallel mechanisms.

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