Latest Papers

ASME Journal of Mechanisms and Robotics

  • Stable Inverse Dynamics for Feedforward Control of Nonminimum-Phase Underactuated Systems
    on January 25, 2023 at 12:00 am

    AbstractAn enhanced inverse dynamics approach is here presented for feedforward control of underactuated multibody systems, such as mechanisms or robots where the number of independent actuators is smaller than the number of degrees of freedom. The method exploits the concept of partitioning the independent coordinates into actuated and unactuated ones (through a QR-decomposition) and of linearly combined output, to obtain the internal dynamics of the nonminimum-phase system and then to stabilize it through proper output redefinition. Then, the exact algebraic model of the actuated sub-system is inverted, leading to the desired control forces with just minor approximations and no need for pre-actuation. The effectiveness of the proposed approach is assessed by three numerical test cases, by comparing it with some meaningful benchmarks taken from the literature. Finally, experimental verification through an underactuated robotic arm with two degrees of freedom is performed.

Vision-Based Control of a Mobile Manipulator With an Adaptable-Passive Suspension for Unstructured Environments

Abstract

The kinematic design, development, and navigation control of a new autonomous mobile manipulator for unstructured terrain is presented in this work. An innovative suspension system is designed based on the kinematic synthesis of an adaptable, passive mechanism. This novel suspension can compensate for irregularities in the terrain by using two pairs of bogies joined by a crank-slider mechanism and facilitates the control of the robotic platform using video cameras. The mobile robot is also equipped with a robotic manipulator, of which a synthesis, simulation, and experimental validation are presented. Additionally, manipulation is accomplished during motion on rough terrain. The proposed mobile robot has been fabricated using additive manufacturing (AM) techniques. A vision-based control approach, from here on named mobile linear-camera space manipulation (MLCSM), for mobile manipulators has been synthesized and implemented to conduct experimental tests. This mobile manipulator has been designed to traverse uneven terrain so that the loading platform is kept close to horizontal while crossing obstacles up to one-third of the size of its wheels. This feature allows for the onboard cameras to stay oriented toward the target; it also allows for any device mounted on the payload platform to remain nearly horizontal during the task. The developed control approach allows us to estimate the position and orientation of the manipulator’s end effector and update its trajectory along the path toward the target. The experiments show a final precision for engagement of a pallet within +/−2.5 mm in position and +/−2 deg in orientation
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