Latest Papers

ASME Journal of Mechanisms and Robotics

  • Intuitive Physical Human–Robot Interaction Using an Underactuated Redundant Manipulator With Complete Spatial Rotational Capabilities
    by Audet JM, Gosselin C. on July 21, 2021 at 12:00 am

    AbstractIn this paper, the concept of underactuated redundancy is presented using a novel spatial two-degrees-of-freedom (2-DoF) gravity-balanced rotational manipulator, composed of movable counterweights. The proposed kinematic arrangement makes it possible to intuitively manipulate a payload undergoing 3-DoF spatial rotations by adding a third rotational axis oriented in the direction of gravity. The static equilibrium equations of the 2-DoF architecture are first described in order to provide the required configuration of the counterweights for a statically balanced mechanism. A method for calibrating the mechanism, which establishes the coefficients of the static equilibrium equations, is also presented. In order to both translate and rotate the payload during manipulation, the rotational manipulator is mounted on an existing translational manipulator. Experimental validations of both systems are presented to demonstrate the intuitive and responsive behavior of the manipulators during physical human–robot interactions.

  • Special Section: Mobile Robots and Unmanned Ground Vehicles
    by Reina G, Das TK, Quaglia G, et al. on July 21, 2021 at 12:00 am

    Inspired by the fifth-year anniversary celebration of the homonymous symposium at the International Mechanical Engineering Congress & Exposition (IMECE), this Special Section with ten articles shares the latest research efforts in design, theory, development, and applications for mobile robots and unmanned ground vehicles.

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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