Latest Papers

ASME Journal of Mechanisms and Robotics

  • Dynamics of Mobile Manipulators Using Dual Quaternion Algebra
    on September 14, 2022 at 12:00 am

    AbstractThis article presents two approaches to obtain the dynamical equations of mobile manipulators using dual quaternion algebra. The first one is based on a general recursive Newton–Euler formulation and uses twists and wrenches, which are propagated through high-level algebraic operations and works for any type of joints and arbitrary parameterizations. The second approach is based on Gauss’s Principle of Least Constraint (GPLC) and includes arbitrary equality constraints. In addition to showing the connections of GPLC with Gibbs–Appell and Kane’s equations, we use it to model a nonholonomic mobile manipulator. Our current formulations are more general than their counterparts in the state of the art, although GPLC is more computationally expensive, and simulation results show that they are as accurate as the classic recursive Newton–Euler algorithm.

Geometric Constraint-Based Reconfiguration and Self-Motions of a Four-CRU Parallel Mechanism


Over the past few years, the concept of multi-directional three-dimensional (3D) printing has been introduced to print complex shapes and overhang geometry. This technique requires the nozzle to constantly change orientation to print the object along its tangential direction. A six-degrees-of-freedom (6-DOF) robotic arm or Stewart platform can be a solution, but these mechanisms use more components and motors. An alternative solution has been proposed in this paper based on a four-CRU (cylindrical, revolute, and universal joints) mechanism. This mechanism can orient the nozzle by switching into different motion types with minimal numbers of motors while keeping the mechanism rigid and agile. Therefore, analyses of the reconfiguration, workspace, singularities, and self-motions of a four-CRU mechanism presented in this paper have become necessities. By using primary decomposition, four geometric constraints have been identified, and the reconfiguration analysis has been carried out in each of these. It reveals that each geometric constraint will have three distinct operation modes, namely Schönflies mode, reversed Schönflies mode, and an additional mode. The additional mode can either be a four-DOF mode or a degenerated three-DOF mode, depending on the type of geometric constraints. By taking into account the actuation and constraint singularities, the workspace of each operation mode has been analyzed and geometrically illustrated. It allows us to determine the regions in which the reconfiguration takes place. Furthermore, the inherent self-motion in the Schönflies mode is revealed and illustrated, which occurs at two specified actuated leg lengths. Demonstration of the reconfiguration process and self-motions is provided through a mock-up prototype.
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