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.

Design of the Wearable Spatial Gravity Balance Mechanism


Gravity compensation mechanisms are widely used in manipulators and exoskeletons as passive components that generate counter-gravity force and save energy. While there have been making great progresses in the design of gravity compensators, a strict condition that the axes of the gravity compensators are aligned with the axes of the links being balanced (LBBs) exactly is usually assumed implicitly, which is difficult to achieve for exoskeletons in practice. In this paper, the design method of the wearable spatial gravity compensator compatible to the misalignment between the rotation centers of the LBB and the compensator is carefully studied. First, the design of the planar gravity compensation unit (PGCU) is presented for each link when rotating in the yaw plane, and next, the PGCU is adapted into the spatial gravity compensation unit (SGCU) to accommodate the general rotation of the LBB. Then, the type synthesis of the SGCU is conducted followed by the analyses of the acting patterns of synthesized SGCUs on the LBBs and gravity compensation performances when the misalignments occur. Finally, the SGCUs are combined with timing belt mechanisms (TBMs) to construct gravity compensation mechanisms for spatial serial linkages. Simulations of an exoskeleton constructed by SGCUs are conducted to verify the performance of gravity balance and the effectiveness of the proposed design method.

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