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.

A Walking Claw for Tethered Object Retrieval

Abstract

Mobility and manipulation are often considered separately, with independent degrees-of-freedom (DOF) for each. However, here we show that using the legs for both walking and grasping increases the versatility of both tasks. Our robot has four DOF: drive and lift for left and right pairs of legs. The legs use a reduced actuation Klann mechanism. The lift DOF rotates the entire trajectory of the legs, which enables gait modulation, climbing, and grasping. This demonstrates the feasibility of a novel operational concept: a robot that can approach, climb onto, and securely grasp an object that can then be lifted via a load-bearing tether. Specifically, we show the kinematics to enable small robots to climb onto rectangular objects up to 67% robot height and grasp objects between 43% and 72% of the robot’s length. With these kinematics, a robot can be scaled for specific terrains and object sizes, with potential application in construction, search and rescue, and object retrieval.

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